What physiological characteristics of anadromous fish allow them. Opportunities for breeding anadromous fish in brackish water. Ecological groups of fish

Water as a living environment has a number of specific features that create unique conditions for existence.

The life arena of fish is exceptionally large. With a total surface of the globe equal to approximately 510 million square meters. km, about 361 million sq. km, that is, 71% of the entire area is occupied by the surface of the oceans and seas. In addition, about 2.5 million square meters. km, or 0.5% of the world's area, is occupied by inland water bodies. The vastness of the life arena is determined, in addition, by its great vertical strike. The maximum known depth of the ocean is approximately 11 thousand meters. Oceans with a depth of more than 3 thousand meters occupy approximately 51-58% of the entire area of ​​sea waters. Further, it should be taken into account that fish live in areas located from the equator to the polar regions; they are found in mountain reservoirs at an altitude of more than 6 thousand and above sea level and in oceans at a depth of more than 10 thousand meters. All this creates a wide variety of living conditions. Let us analyze some of the features of the aquatic habitat in relation to the fish inhabiting it.

The mobility of the aquatic environment is associated with constant currents in rivers and seas, local currents in small closed water bodies, vertical displacements of water layers due to their different heating.

The mobility of water largely determines the passive movements of fish. For example, the larvae of Norwegian herring, which hatched off the coast of Western Scandinavia, are carried away by one of the branches of the Gulf Stream to the northeast and in 3 months they move along the coast for 1000 km.

The fry of many salmonids hatch at the tops of tributaries of large rivers, and they spend most of their life in the seas. The passage from rivers to seas is also largely passive; they are carried into the seas by river currents.

Finally, the mobility of water determines the passive movement of food items - plankton, which in turn affects the movement of fish.

Temperature fluctuations in the aquatic environment are much less than in the air-ground environment. In the overwhelming majority of cases, the upper limit of the temperature at which fish are found lies below +30, + 40 ° С.The lower limit of water temperature is especially characteristic, which even in highly salty parts of the oceans does not fall below -2 ° С.Consequently, the real amplitude fish habitat temperatures are only 35-45 ° С.

At the same time, it must be taken into account that even these relatively limited temperature fluctuations are of great importance in the life of fish. The influence of temperature is carried out both by direct influence on the fish organism, and indirectly, through a change in the ability of water to dissolve gases.

As you know, fish belong to the so-called cold-blooded animals. Their body temperature does not remain more or less constant, as in warm-blooded animals - it is directly dependent on the ambient temperature. This is due to the physiological characteristics of organisms, in particular with the nature of the process of heat generation. In fish, this process is much slower. Thus, a carp weighing 105 g emits 42.5 kJ of heat per day per 1 kg of mass, and a starling weighing 74 g per 1 kg of mass emits 1125 kJ per day. It is known that the temperature of the environment, and hence the body temperature of fish, significantly affects such important biological phenomena as the maturation of reproductive products, the development of eggs, and nutrition. A decrease in water temperature causes hibernation in a number of fish. Such are, for example, crucian carp, carp, sturgeon.

The indirect influence of water temperature can be well traced on the features of the phenomena of gas exchange in fish. It is known that the ability of water to dissolve gases, and in particular oxygen, is inversely proportional to its temperature and salinity.

At the same time, the oxygen demand of fish increases as the water temperature rises. In connection with the above, the minimum oxygen concentration changes, below which the fish dies. For carp, it will be equal to: at a temperature of 1 ° С - 0.8 mg / l, at a temperature of 30 ° С - 1.3 mg / l, and at 40 ° С - about 2.0 mg / l.

In conclusion, we point out that the oxygen demand of different fish species is not the same. On this basis, they can be divided into four groups: 1) requiring a lot of oxygen; normal conditions for them are 7-11 cm 3 of oxygen per liter: brown trout (Salmo trutta), minnow (Phoxinus phoxinus), char (Nemachilus barbatulus); 2) requiring a lot of oxygen - 5-7 cm 3 per liter: grayling (Thymallus thymallus), chub (Leuciscus cephalus), gudgeon (Gobio gobio); 3) consuming a relatively small amount of oxygen - about 4 cm 3 per liter: roach (Rutilus rutilus), perch (Perea fluviatilis), ruff (Acerina cernua); 4) withstanding very weak oxygen saturation of water and living even with 1/2 cm 3 of oxygen per liter: carp, tench, crucian carp.

The formation of ice in water bodies is of great importance in the life of fish. The ice cover to a certain extent isolates the underlying water layers from low air temperatures and thereby prevents the reservoir from freezing to the bottom. This makes it possible for fish to spread in areas with very low air temperatures in winter. This is the positive meaning of the ice cover.

The ice cover also plays a negative role in the life of fish. This is reflected in its darkening effect, which slows down or even almost completely stops the life processes in many aquatic organisms that directly or indirectly have food value for fish. First of all, this concerns green algae and higher plants, which are fed partly by the fish themselves and those invertebrates that the fish eat.

Ice cover drastically reduces the possibility of oxygen replenishment of water from the air. In many reservoirs in winter, as a result of putrefactive processes, oxygen dissolved in the water is completely lost. There is a phenomenon known as the death of water bodies. In our country, it is widespread and is observed in basins, the drainage area of ​​which is largely associated with bogs (more often peat bogs). Large kills were observed in the Ob basin. The swamp waters that feed the rivers here are rich in humic acids and ferrous compounds. These latter, being oxidized, take away the oxygen dissolved in it from the water. Its compensation from the air is impossible due to the continuous cover of ice.

From the rivers of the vast territory of Western Siberia, fish begin to descend into the Ob in December and, following it down, reach the Ob Bay in March. In the spring, as the ice melts, the fish rises back (the so-called plunge movement of the fish). Zamora is also observed in the European part of Russia. They are successfully combating deaths by constructing ice holes or by increasing the flow of a pond or lake. In pond farms with high technical equipment, compressors are used that pump water with oxygen. One of the methods of fishing is based on the approach of fish to the ice holes or to the heated ditches specially constructed in the shores of the lake. It is curious that the settlement of beavers and muskrats on some of the water bodies subject to death has weakened this phenomenon, since gas exchange between water bodies and the atmosphere is facilitated through holes, huts and other structures of these animals.

The sound conductivity of water is very high. This circumstance is widely used by fish, among which sound signaling is widely developed. It provides information both among individuals of one species and signals about the presence of individuals of other species. It is possible that the sounds emitted by fish have echolocation significance.

Ecological groups of fish

Sea fish

This is the most numerous group of species that spend their entire life in salty sea water. They inhabit a variety of horizons, and on this basis, such groups should be distinguished.

1. Pelagic fish. They live in the water column, in which they widely move in search of food and places suitable for breeding. The overwhelming majority swim actively and have an elongated, fusiform body; such are, for example, sharks, sardines, mackerels. Few, such as the moonfish, move largely passively with currents of water.

2. Littoral bottom fish. They live in the bottom layers of water or at the bottom. Here they find food, spawn and escape from persecution. Distributed at various depths, from shallow waters (rays, some flounders, gobies) to significant depths (chimera).

Swimming ability is worse than that of the previous group. Many have a variety of devices for passive protection in the form of thorns, thorns (some rays, gobies), a thick outer shell (box).

3. Abyssal fish. A small group inhabiting deep-water (below 200 m) parts of the seas and oceans. The conditions of their existence are extremely peculiar and generally unfavorable. This is due to the absence of light at great depths, low temperatures (no higher than + 4 ° C, more often about 0 ° C), tremendous pressure, higher salinity of water, and the absence of plant organisms. Abyssal fish are partly devoid of eyes, partly, on the contrary, they have huge telescopic eyes; some have glow organs that make it easier to find food. Due to the absence of plants, all abyssal fish are carnivorous; they are either predators or carrion eaters.

Freshwater fish

Freshwater fish live only in fresh water bodies, from which they do not even enter the salinized pre-estuarine areas of the seas. Depending on the type of reservoir among freshwater fish, the following groups are distinguished:

1. Fish of stagnant waters live in lakes and ponds (crucian carp, tench, some whitefish).

2. Common freshwater fish inhabit stagnant and flowing waters (pike, perch).

3. Fish of flowing waters. As an example, you can point to trout, asp.

Anadromous fish

Anadromous fish, depending on the stage of their life cycle, live either in the seas or in rivers. Almost all anadromous fish spend the period of growth and maturation of reproductive products in the sea, and go to rivers for spawning. These are many salmon (chum, pink salmon, salmon), sturgeon (sturgeon, beluga), some herring. As an opposite example, it is necessary to point to river eels (European and American), which breed in the sea (Atlantic Ocean), and the period of preparation for spawning is spent in rivers.

Fish of this group often make very long migrations of 1000 kilometers or more. So, chum salmon from the northern part of the Pacific Ocean enters the Amur, along which it rises (some shoals) above Khabarovsk. European eel from the rivers of Northern Europe goes for spawning in the Sargasso Sea, i.e., the western part of the Atlantic Ocean.

Semi-anadromous fish

Semi-anadromous fish live in the pre-estuarine desalinated parts of the seas, and for reproduction, and in some cases for wintering, they enter rivers. However, unlike true anadromous fish, they do not climb high rivers. Such are the vobla, bream, carp, catfish. In some places, these fish can live and settled in fresh water bodies. The group of semi-anadromous fish is the least natural.

Body shape of some fish groups

Due to the exceptional diversity of habitat conditions, the appearance of fish is also extremely diverse. Most of the species inhabiting open areas of water bodies have a fusiform body, often somewhat laterally compressed. They are good swimmers, since the speed of swimming in these conditions is necessary both for predatory fish when catching prey, and for peaceful fish forced to escape from numerous predators. These are sharks, salmon, herring. Their main organ of translational movement is the caudal fin.

Among the fish living in open parts of water bodies, the so-called planktonic fish are relatively few. They live in the water column, but often move passively along with the currents. Outwardly, most of them are distinguished by a shortened, but highly expanded body, sometimes almost spherical in shape. Fins are very poorly developed. Examples include hedgehog fish (Diodon) and melanocetus (Melanocetus). The fish-moon (Mola mola) has a very high body, laterally compressed. It has no tail and pelvic fins. The puffer (Spheroides), after filling the intestines with air, becomes almost spherical and floats downstream with its belly up.

The bottom fish are much more numerous and diverse. Deep-sea species often have a drop-like shape, in which the fish has a large head and a body gradually thinning towards the tail. Such are the long-tailed (Macrurus norvegicus) and chimera (Chimaera monstrosa) from cartilaginous fish. Similar in body shape to them are cod and eelpout, living in the bottom layers, sometimes at considerable depths. The second type of benthic deep-sea fishes are slopes flattened in the dorsal-abdominal direction and flounder flattened from the sides. These are sedentary fish that also feed on slow-moving animals. Among bottom-dwelling fish, there are species with a serpentine body - eels, sea needles, loaches. They live among thickets of aquatic vegetation, and their movement is similar to the movement of snakes. Finally, we will mention the peculiar box bodies (Ostracion), the body of which is enclosed in a bony shell that protects the fish from the harmful effects of the surf.

Life cycle of fish, migration

Like all living things, fish need different environmental conditions at different stages of their life. So, the conditions necessary for spawning are different from the conditions that ensure the best feeding of fish, peculiar conditions are needed for wintering, etc. All this leads to the fact that in search of conditions suitable for each given life function, fish perform more or less significant displacement. In species inhabiting small closed bodies of water (ponds, lakes) or rivers, movements are negligible, although in this case they are still quite clearly expressed. In marine fish and especially in anadromous fish, migrations are most developed.

The most complex and varied are spawning migrations in anadromous fish; they are associated with the transition from seas to rivers (more often) or, conversely, from rivers to seas (less often).

The transition for reproduction from seas to rivers (anadromous migrations) is characteristic of many salmon, sturgeon, some herring and cyprinids. There are significantly fewer species feeding in rivers and going to the seas for spawning. Such movements are called catadromous migrations. They are common with acne. Finally, many purely marine fish make long movements in connection with spawning, moving from the open sea to the shores or, conversely, from the coast to the depths of the sea. These are sea herring, cod, haddock, etc.

The length of the spawning migration path is very different depending on the type of fish and the conditions of the water bodies inhabited by them. So, the species of semi-anadromous cyprinids of the northern part of the Caspian Sea rise up the rivers by only a few tens of kilometers.

Many salmonids make huge migrations. In the Far Eastern salmon - chum salmon - the migration route reaches in places two or more thousand kilometers, and in the sockeye salmon (Oncorhynchus nerka) - about 4 thousand km.

Salmon rises along the Pechora to its headwaters. The European river eel, which breeds in the western part of the Atlantic Ocean, passes several thousand kilometers on its way to the spawning grounds.

The length of the migratory route depends on how adapted the fish are to the conditions in which spawning can take place, and in this connection, and on how far from the feeding grounds there are places suitable for spawning.

The time of spawning migrations in fish generally cannot be indicated as definitely as, for example, the timing of migrations of birds to their nesting sites. This is due, firstly, to the fact that the timing of spawning in fish is very diverse. Secondly, there are many cases when fish approach the spawning grounds almost six months before spawning. So, for example, the White Sea salmon enters the rivers in two terms. In autumn, there are individuals with relatively underdeveloped reproductive products. They hibernate in the river and breed the next year. Along with this, there is another biological race of the White Sea salmon, which enters the rivers in summer - the reproductive products of these individuals are well developed, and they spawn in the same year. Chum salmon also have two spawning runs. Summer chum salmon enters Amur in June - July, and autumn chum salmon - in August - September. Unlike salmon, both biological races of chum salmon spawn in the year they enter the river. Vobla enters rivers for spawning in spring, some whitefish, on the contrary, migrate to breeding grounds only in autumn.

Here are generalized descriptions of spawning migrations of some fish species.

Before breeding, Norwegian sea herring are fed far northwest of Scandinavia, near the Faroe Islands, and even in the waters off Svalbard. At the end of winter, shoals of herring begin to move towards the coast of Norway, which they reach in February-March. Spawning occurs in fjords near the coast in shallow areas. Heavy caviar, swept out by fish, settles in huge quantities to the bottom and sticks to algae and stones. The hatched larvae only partly remain in the fiords; most of them are carried away by the North Cape Current (the northeastern branch of the Gulf Stream) along the coast of Scandinavia to the north. The larvae often begin such passive migration at a very early age, when they retain the yolk bladder. For three to four months, until the end of July - early August, they cover a distance of 1000 - 1200 km and reach the shores of Finnmarken.

Young herring pass their way back actively, but much more slowly - in four to five years. They move south in stages every year, either approaching the shores or going out into the open sea. At the age of four or five, the herring becomes sexually mature, and by this time it reaches the spawning area - the place where it was born. This ends the first, "youthful" stage of her life - the period of a long journey to the north.

The second period, the period of maturity, is associated with annual migrations from the feeding area to the spawning area and vice versa.

According to another hypothesis, anadromous fish were primordially marine and their entry into rivers is a secondary phenomenon associated with strong desalination of the seas during the melting of glaciers, which in turn allowed the fish to more easily adapt to life in fresh water. One way or another, but there is no doubt that anadromous salmon change their habitat depending on the characteristics of the biological state. Adult fish inhabit vast areas of the seas, rich in food. Their juveniles hatch in cramped fresh water bodies (upper reaches of rivers), where the existence of the entire mass of grown fish would be impossible due to the limited space itself and due to lack of food. However, conditions for hatching juveniles are more favorable here than in the sea. This is due to clean, oxygen-rich water, the possibility of burying eggs in the bottom soil and the possibility of its successful development in porous soil. All this is so favorable for the success of reproduction that the number of eggs, ensuring the preservation of the species, reaches, for example, in pink salmon only 1100-1800 eggs.

Forage migrations on one scale or another are characteristic of almost all fish. Naturally, in small enclosed bodies of water, the movement of fish in search of food is very limited and outwardly differs sharply from the long and massive wanderings observed in marine or anadromous fish.

The nature of forage migrations in a general sense is quite understandable if we take into account that during the spawning period, fish choose very specific environmental conditions, which, as a rule, are not of great value in terms of forage. Let us recall, for example, that salmon and sturgeon spawn in rivers with their very limited feeding possibilities for huge masses of fish that have entered. This circumstance alone should cause the movement of fish after spawning. In addition, most fish stop feeding during reproduction, and, therefore, after spawning, the need for food increases sharply. In turn, the foregoing forces the fish to seek areas with especially favorable feeding opportunities, which enhances their movement. There are many examples of forage migrations among various biological groups of fish.

European salmon - salmon, in contrast to its Pacific congener, chum salmon, does not die completely after spawning, and the movement of spawning fish down the river should be considered as forage migrations. But even after the fish leave the sea, they make massive regular migrations in search of places especially rich in food.

Thus, the Caspian stellate sturgeon, which emerged from the Kura after spawning, crosses the Caspian Sea and feeds mainly on the eastern coast of the Caspian. The juveniles of chum salmon, which rolled down the Amur in the next (after spawning) spring, are fed to the shores of the Japanese Islands.

Not only anadromous, but also marine fish show examples of distinct forage migrations. Norwegian herring, spawning in the shallows off the southwestern coast of Scandinavia, does not remain in place after breeding, but moves in masses to the north and northwest, to the Faroe Islands and even to the Greenland Sea. Here, on the border of the warm waters of the Gulf Stream and the cold waters of the Arctic basin, an especially rich plankton develops, on which depleted fish feed on. It is curious that simultaneously with the herring migration to the north, the herring shark (Lanina cornubica) also migrates in the same direction.

Atlantic cod migrates widely in search of food. One of its main spawning grounds is the shallows (banks) of the Lofoten Islands. After breeding, cod becomes extremely voracious, and in search of food, large flocks of it are sent partly along the coast of Scandinavia to the northeast and further east through the Barents Sea to Kolguev Island and Novaya Zemlya, partly to the north, to Bear Island and further to Spitsbergen. This migration is of particular interest to us, since fishing for cod in the Murmansk region and in the Kaninsko-Kolguevsky shallow water is largely based on the catch of migrating and feeding stocks. During migrations, cod adheres to the warm streams of the North Cape Current, along which, according to the latest data, it penetrates through the Kara Gates and the Yugorsky Shar even into the Kara Sea. The largest number of cod in the Barents Sea accumulates in August, but already in September it begins to reverse movement, and by the end of November the large cod that came from the coast of Norway disappears in our waters. By this time, the water temperature drops sharply and becomes unfavorable both for the fish themselves and for the animals that serve them as food. Cod, having fed up and accumulating fat in the liver, begins a reverse movement to the southwest, being guided by the temperature of the water, which serves as a good reference point - an irritant during migrations.

The length of the one-way trip by the cod during the described migrations is 1–2 thousand km. Fish move at a speed of 4-11 nautical miles per day.

Along with horizontal migrations, there are cases of vertical movements of marine fish in search of food. Mackerel rises into the surface layers of water when the richest development of plankton is observed here. When plankton descends into deeper layers, mackerel also descends there.

Winter migrations. When the water temperature drops in winter, many species of fish become inactive or even go into a state of numbness. In this case, they usually do not remain in the feeding grounds, but gather in confined areas, where the conditions of the relief, bottom, soil and temperature are favorable for wintering. So, carp, bream, pike perch migrate to the lower reaches of the Volga, Ural, Kura and other large rivers, where, accumulating in huge numbers, they lie in pits. The wintering of sturgeons in pits on the Ural River has long been known. In summer, our Pacific flounders are distributed throughout the Peter the Great Bay, where they do not form large concentrations. In autumn, as the water temperature decreases, these fish move from the coast to the depths and gather in few places.
The physical reason that causes a kind of hibernation in fish is a decrease in water temperature. In hibernation, fish lie motionless on the bottom, more often in the depressions of the bottom - pits, where they often accumulate in huge numbers. In many species, the surface of the body at this time is covered with a thick layer of mucus, which to a certain extent isolates the fish from the negative effects of low temperatures. The metabolism of fish wintering in this way is extremely reduced. Some fish, such as crucian carp, hibernate by burying themselves in silt. There are cases when they freeze into the silt and successfully overwinter if the "juices" of their bodies are not frozen. Experiments have shown that ice can surround the entire body of a fish, but the internal "juices" remain unfrozen and have temperatures down to -0.2, -0.3 ° C.

Wintering migrations do not always end with the fish falling into a state of numbness. So, the Azov anchovy, at the end of feeding for the winter, leaves the Sea of ​​Azov to the Black Sea. This is apparently due to the unfavorable temperature and oxygen conditions that arise in the Sea of ​​Azov in winter in connection with the appearance of an ice cover and strong cooling of the water of this shallow reservoir.

A number of the above examples show that the life cycle of fish consists of a number of successive stages: maturation, reproduction, feeding, wintering. During each stage of the life cycle, fish need different specific environmental conditions, which they find in different, often far apart places of the water body, and sometimes in different water bodies. The degree of development of migration is not the same for different fish species. The greatest development of migration is obtained in anadromous fish and fish living in the open seas. This is understandable, since the variety of environmental conditions in this case is very great and in the process of evolution, fish could develop an important biological adaptation - significantly change habitats depending on the stage of the biological cycle. Naturally, in fish inhabiting small and especially closed water bodies, migrations are less developed, which also corresponds to a smaller variety of conditions in such water bodies.

The nature of the life cycle in fish is different in other ways as well.

Some fish, and most of them, spawn annually (or at some intervals), repeating the same movements. Others during their life cycle only go through the stage of maturation of reproductive products, once they undertake spawning migration, and reproduce only once in their life. These are some types of salmon (chum salmon, pink salmon), river eels.

Nutrition

The nature of fish food is extremely varied. Fish feed on almost all living things that live in the water: from the smallest planktonic plant and animal organisms to large vertebrates. At the same time, relatively few species feed only on plant food, while the majority eat animal organisms or mixed animal-plant food. The division of fish into predatory and peaceful ones is largely arbitrary, since the nature of the food varies significantly depending on the conditions of the reservoir, the season and the age of the fish.

Particularly specialized herbivorous species are plankton silverheads (Hyspophthalmichthys) and grass-eating grass carps (Ctenopharyngodon).

Of the fish of our fauna, the predominantly plant species are the following: rudd (Scardinius), marinka (Schizothorax) and snort (Varicorhinus). Most fish feed on mixed foods. However, at a young age, all fish go through the stage of peaceful feeding on plankton and only later they switch to their own food (benthos, nekton, plankton). In predators, the transition to the fish table occurs at different ages. So, pike begins to swallow fish larvae, reaching a body length of only 25-33 mm, pike perch - 33-35 mm; Perch, on the other hand, switches to fish feeding relatively late, with a body length of 50-150 mm, while invertebrates still form the main food of the perch during the first 2-3 years of its life.

Due to the nature of the diet, the structure of the mouth apparatus in fish is significantly different. In predatory species, the mouth is armed with sharp teeth bent back, which sit on the jaws (and in fish with a bone skeleton, it is often also on the palatine bones and on the vomer). Stingrays and chimeras feeding on bottom invertebrates dressed in shells or shells have teeth in the form of wide flat plates. In fish gnawing corals, the teeth look like incisors and often grow together into one whole, forming a sharp cutting beak. These are the teeth of the joint-maxillary (Plectognathi).

In addition to the real jaw teeth, some fish also develop the so-called pharyngeal teeth, which sit on the inner edges of the gill arches. In cyprinids, they are located on the lower part of the rear modified branchial arch and are called the lower pharyngeal teeth. These teeth grind food against the corneous corpus callosum, located on the underside of the cerebral skull, the so-called millstone. Wrasses (Labridae) have upper and lower pharyngeal teeth opposite each other; there is no millstone in this case. In the presence of pharyngeal teeth, real jaw teeth are either absent altogether, or poorly developed and only help grasp and hold food.

Adaptation to the type of food is visible not only in the structure of the teeth, but also in the structure of the entire oral apparatus. There are several types of oral apparatus, the most important of which are as follows:

1. The grasping mouth is wide, with sharp teeth on the jaw bones, and often on the vomer and palatine bones. The branchial stamens in this case are short and serve to protect the branchial lobes, and not to filter food. Typical for predatory fish: pike, pike perch, catfish and many others.

2. The mouth of the plankton-eater is of medium size, usually not retractable; teeth are small or missing. The branchial stamens are long, acting like a sieve. Typical for herring, whitefish, some carp.

3. The suction mouth has the appearance of a more or less long tube, sometimes extending. Works as a suction pipette when feeding on benthic invertebrates or small planktonic organisms. Such is the mouth of a bream, a sea needle. This type of mouth apparatus was especially developed in African longnose snouts (Mormyridae), which, in search of food, thrust their tube-shaped snout under stones or into silt.

4. The mouth of the benthos-eater - stingrays, flounders, sturgeons - is located on the underside of the head, which is associated with the extraction of food from the bottom. In some cases, the mouth is armed with powerful millstone teeth that serve to crush shells and shells.

5. Mouth with striking or xiphoid jaws or snout. In this case, the jaws (garfish - Belonidae) or snout (rays, saw-fish - Pristis, pylon-nosed sharks - Pristiophorus) are strongly elongated and serve to attack schools of fish, such as herring. There are other types of oral apparatus, a complete list of which need not be given here. In conclusion, we note that even in systematically close fish, one can easily see differences in the structure of the mouth, associated with the nature of nutrition. An example is carp fish that feed on bottom, then planktonic, then animals falling to the surface of the water.

The intestinal tract also varies significantly depending on the nature of the diet. In predatory fish, as a rule, the intestines are short and the stomach is well developed. In fish that feed on mixed or plant foods, the intestines are much longer, and the stomach is weakly isolated or completely absent. If in the first case the intestine is only slightly longer than the body length, then in some herbivorous species, for example, in the Trans-Caspian temple (Varicorhinus), it is 7 times longer than the body, and in the crowd (Hypophthalmichthys), which feeds almost exclusively on phytoplankton, the intestinal tract is 13 times larger than body length of the fish.

The methods of obtaining food are varied. Many predators pursue their prey directly, overtaking it in open water. These are sharks, asp, pike perch. There are predators stalking prey and grabbing it shortly. In case of an unsuccessful throw, they make no attempts to chase prey over a long distance. This is how, for example, pikes and catfish hunt. It has already been indicated above that the saw-fish and the pilonos use their xiphoid organ when hunting. They crash into schools of fish with great speed and make several strong blows with the "sword", which kill or stun the victim. The insectivorous archerfish (T.oxotes jaculator) has a special device by means of which it throws out a strong stream of water, knocking insects off the coastal vegetation.

Many bottom fish are adapted to digging out the ground and taking out food items from it. Carp is able to get food, penetrating into the soil to a depth of 15 cm, bream - only up to 5 cm, while the perch practically does not take food in the ground at all. The American polyodon (Polyodon) and the Central Asian shovelnose (Pseudoscaphirhynchus) successfully dig in the ground, using their rostrum for this (both fish from the cartilaginous subclass).

An extremely peculiar device for getting food from an electric eel. This fish, before grabbing its prey, strikes it with an electric discharge that reaches 300 volts in large individuals. Eel can discharge randomly and several times in a row.

The intensity of feeding of fish throughout the year and in general of the life cycle is not the same. The overwhelming majority of species stop feeding during the spawning period and lose a lot of weight. Thus, in Atlantic salmon, muscle mass is reduced by more than 30%. In this regard, their need for food is extremely high. The post-spawning period is called the period of restorative feeding, or "zhora".

Reproduction

The vast majority of fish are dioecious. The exception is a few bony fish: sea bass (Serranus scriba), gilthead (Chrysophrys) and some others. As a rule, in the case of hermaphroditism, the sex glands alternately function as the testes, then as the ovaries, and self-fertilization is therefore impossible. Only in seabass, different parts of the gonad simultaneously secrete eggs and sperm. Sometimes hermaphrodite individuals are found in cod, mackerel, and herring.

In some fish, parthenogenetic development is sometimes observed, which, however, does not lead to the formation of a normal larva. In salmon, unfertilized eggs laid in the nest do not die and develop in a peculiar way until the time when embryos are hatched from the fertilized eggs. This is a very peculiar adaptation to the preservation of the clutch, since if its unfertilized eggs developed, and died and decomposed, this would lead to the death of the entire nest (Nikolsky and Soin, 1954). In Baltic herring and herring, parthenogenetic development sometimes reaches the stage of a free-swimming larva. There are other examples of this kind. However, in no case does parthenogenetic development lead to the formation of viable individuals.

In fish, another type of deviation from normal reproduction is known, called gynogenesis. In this case, the sperm penetrate the egg, but the fusion of the egg nuclei and the sperm does not occur. Some fish species develop normally, but only one female is produced in the offspring. This is the case with the goldfish. Both females and males of this species are found in East Asia, and reproduction proceeds normally. In Central Asia, Western Siberia and Europe, males are extremely rare, and in some populations they are not at all. In such cases, insemination, leading to gynogenesis, is carried out by males of other fish species (N "Kolsky, 1961).

Compared with other vertebrates, fish are characterized by tremendous fertility. Suffice it to point out that most species lay hundreds of thousands of eggs per year, some, such as cod, up to 10 million, and moonfish even hundreds of millions of eggs. In connection with the foregoing, the size of the gonads in fish is generally relatively large, and by the time of reproduction the gonads increase even more sharply. There are frequent cases when the mass of the gonads at this time is equal to 25 or even more percent of the total body weight. The enormous fertility of fish is understandable if we consider that the eggs of the overwhelming majority of species are fertilized outside the mother's body, when the probability of fertilization is sharply reduced. In addition, spermatozoa retain the ability to fertilize in water for a very short time: for a short time, although it differs depending on the conditions in which spawning takes place. So, in chum salmon and pink salmon, spawning in a fast course, where the contact of sperm with eggs can be carried out in a very short period of time, sperm retain their mobility only for 10-15 seconds. For Russian sturgeon and stellate sturgeon, spawning in a slower course, it is 230 - 290 seconds. In Volga herring, a minute after placing the sperm in the water, only 10% of the sperm retained mobility, and after 10 minutes only single spermatozoa moved. In species spawning in relatively sedentary water, spermatozoa remain mobile longer. So, in oceanic herring, spermatozoa retain the ability to fertilize for more than a day.

Eggs, getting into water, produce a vitreous membrane, which soon prevents sperm from penetrating inside. All this reduces the likelihood of fertilization. Experimental calculations have shown that in salmon of the Far East, the percentage of fertilized eggs is 80%. In some fish, this percentage is even lower.

In addition, eggs develop, as a rule, directly in the aquatic environment, they are not protected or protected by anything. Due to this, the probability of death of developing eggs, larvae and fry of fish is very high. For the commercial fish of the North Caspian, it was found that of all the larvae hatched from the eggs, no more than 10% rolls into the sea in the form of formed fish, while the remaining 90% die (Nikolsky, 1944).

The percentage of fish surviving to maturity is very small. For example, for stellate sturgeon it is determined at 0.01%, for autumn chum salmon Amur - 0.13-0.58, for Atlantic salmon - 0.125, for bream - 0.006-0.022% (Chefras, 1956).

Thus, it is obvious that the enormous initial fecundity of fish serves as an important biological adaptation for the conservation of species. The validity of this position is also proved by the clear relationship between fertility and the conditions under which reproduction occurs.

The most fertile are marine pelagic fish and fish with floating eggs (millions of eggs). The probability of death of the latter is especially high, since it can easily be eaten by other fish, washed ashore, etc. Fish that lay heavy eggs that settle to the bottom, which, moreover, usually stick to algae or stones, have less fertility. Many salmonids lay their eggs in pits specially built by fish, and some then cover these pits with small pebbles. In these cases, therefore, there are the first signs of "caring for the offspring." Accordingly, fertility also decreases. So, salmon spawns from 6 to 20 thousand eggs, chum salmon - 2-5 thousand, and pink salmon - 1-2 thousand.We point out, for comparison, that stellate sturgeon lays up to 400 thousand eggs, sturgeon - 400-2500 thousand, beluga - 300-8000 thousand, pike perch - 300-900 thousand, carp 400-1500 thousand, cod - 2500-10 000 thousand

The three-spined stickleback lays eggs in a special nest made of plants, and the male guards the eggs. The number of eggs in this fish is 20-100. Finally, most cartilaginous fish with internal insemination, a complex shell of eggs (which they strengthen on stones or algae), lay eggs in units or tens.

In most fish, fertility increases with age and only slightly decreases with age. It should be borne in mind that most of our commercial fish do not survive to the age of aging, since by this time they are already caught.
As already partly indicated, the vast majority of fish are characterized by external fertilization. The exception is almost all modern cartilaginous fish and some bony ones. In the former, the extreme internal rays of the pelvic fins function as a copulatory organ, which they put together during mating and enter into the cloaca of the female. There are many species with internal fertilization among the order of toothed carp (Cyprinodontiformes). The copulatory organ in these fish is the modified rays of the anal fin. Internal fertilization is characteristic of the seabass (Sebastes marinus). However, he does not have copulatory organs.

Unlike most vertebrates, fish (if we talk about a superclass in general) do not have a specific breeding season. According to the spawning time, at least three groups of fish can be distinguished:

1. Spawning in spring and early summer - sturgeon, carp, catfish, herring, pike, perch, etc.

2. Spawning in autumn and winter - these include mainly fish of northern origin. Thus, Atlantic salmon begins to spawn in our country from the beginning of September; the spawning period extends depending on the age of the fish and the conditions of the reservoir until the end of November. River trout spawns in late autumn. Whitefish spawn in September - November. Of marine fish, cod spawns in Finnish waters from December to June, and off the coast of Murmansk from January to late June.

As mentioned above, anadromous fish have biological races that differ in the time they enter rivers for spawning. Such races are, for example, in chum salmon and salmon.

3. Finally, there is a third group of fish that do not have a specific breeding period. These include mainly tropical species, the temperature conditions of which do not change significantly during the year. Such are, for example, the species of the Cichlidae family.

Spawning grounds are extremely diverse. In the sea, fish lay eggs, starting from the ebb and flow zone, for example, pingagoras (Cyclopterus), atherina (Laurestes) and a number of others, and up to depths of 500-1000 m, where eels, some flounders, etc. spawn.

Cod and sea herring spawn near the coast, in relatively shallow places (banks), but already outside the ebb and flow zone. Spawning conditions in rivers are no less varied. Bream in the downstream ilmen of the Volga lays eggs on aquatic plants. Asp, on the contrary, chooses places with a rocky bottom and a fast current. In creeks overgrown with algae, perches spawn, which attach eggs to underwater vegetation. In very shallow places, entering small rivers and ditches, pikes spawn.

The conditions in which eggs are found after fertilization are very diverse. Most fish species leave her to her fate. Some, however, place eggs in special structures and protect them for more or less a long time. Finally, there are cases when fish carry fertilized eggs on their bodies or even inside their bodies.

Let us give examples of such “care for offspring”. Chum salmon spawning grounds are located in shallow tributaries of the Amur, in places with pebble soil and relatively calm current, 0.5-1.2 m deep; at the same time, it is important to have underground springs that provide clean water. The female, accompanied by one or more males, having found a place suitable for laying eggs, lies down on the bottom and convulsively bending, clears it of grass and silt, raising a cloud of turbidity. Further, the female pulls out a hole in the ground, which is also done by blows of the tail and bending the whole body. After the construction of the pit, the spawning process begins. The female, being in the pit, releases eggs, and the male next to her releases milk. Several males usually stand near the pit, and there are often fights between them.

The eggs are laid in the pit in nests, of which there are usually three. Each nest is covered with pebbles, and when the construction of the last nest is completed, the female pours an oval-shaped mound (2-3 m long and 1.5 m wide) over the pit, which guards for several days, preventing other females from digging a hole for spawning here. Following this, the female dies.

A three-spined stickleback suits an even more complex nest. The male pulls out a hole at the bottom, lines it with scraps of algae, then arranges the side walls and a vault, gluing the plant residues with a sticky secretion of skin glands. When finished, the socket is in the shape of a ball with two holes. Then the male drives the females into the nest one after the other and waters each portion of eggs with milk, after which he guards the nest from enemies for 10-15 days. In this case, the male is positioned relative to the nest in such a way that the movements of his pectoral fins excite the flow of water above the eggs. This, apparently, ensures better aeration, and, consequently, more successful development of eggs.

Further complications of the described phenomenon of "caring for offspring" can be seen in fish that carry fertilized eggs on their bodies.

In the female catfish aspredo (Aspredo laevis), the skin on the belly during the spawning period noticeably thickens and softens. After spawning and fertilization by the male, the female, by the weight of her body, presses the eggs into the skin of the belly. Now the skin looks like small combs, in the cells of which eggs sit. The latter are connected to the mother's body by developing stems supplied with blood vessels.

Male needlefish (Syngnathus acus) and seahorse (Hippocampus) have leathery folds on the underside of the body, forming a kind of egg sac in which females lay eggs. At the sea needle, the folds only bend over the belly and cover the eggs. In the seahorse, the hatching adaptation is even more developed. The edges of the egg sac are tightly fused, a dense network of blood vessels develops on the inner surface of the formed chamber, through which, apparently, gas exchange of embryos is carried out.

There are species that carry eggs in the mouth. This is the case with the American sea catfish (Galeichthys fells), in which the male bears up to 50 eggs in the mouth. At this time, he apparently does not eat. In other species (for example, the genus Tilapia), the female carries eggs in her mouth. Sometimes there are more than 100 eggs in the mouth, which are set in motion by the female, which is apparently associated with the provision of better aeration. The incubation period (judging by the observation in the aquarium) lasts 10-15 days. At this time, the females hardly feed. It is curious that even after hatching, the fry for some time, in case of danger, hide in the mother's mouth.

Let us mention a very peculiar reproduction of the mustard (Rhodeus sericeus) from the cyprinid family, which is widespread in Russia. During the spawning period, the female develops a long ovipositor, with which she lays eggs in the mantle cavity of mollusks (Unio or Anodonta). Here the eggs are fertilized by spermatozoa, which are sucked up by the molluscs with a stream of water through a siphon. (The male excretes milk near the mollusk.) The embryos develop in the gills of the mollusk and go out into the water, reaching a length of about 10 mm.

The last degree of complication of the reproduction process in fish is expressed in vivacity. Fertilized in the oviducts, and sometimes even in the ovarian sac, eggs do not enter the external environment, but develops in the genital tract of the mother. Usually, development is carried out at the expense of the yolk of the egg, and only in the final stages does the embryo feed also due to the secretion of a special nutritious fluid by the walls of the oviduct, which is perceived by the embryo through the mouth or through the spherula. Thus, the described phenomenon is more correctly designated as egg production. However, some sharks (Charcharius Mustelus) develop a peculiar yolk placenta. It arises by establishing a close connection between the outgrowths of the yolk bladder rich in blood vessels and the same formations in the walls of the uterus. Through this system, the metabolism of the developing embryo is carried out.

Ovoviviparity is most characteristic of cartilaginous fish, in which it is observed even more often than oviposition. On the contrary, this phenomenon is observed very rarely among bony fish. As an example, we can point to the Baikal golomyanka (Comephoridae), blend dogs (Blenniidae), sea bass (Serranidae) and especially toothed carp (Cyprinodontidae). All ovoviviparous fish have low fertility. Most give birth to a few cubs, rarely dozens. Exceptions are very rare. So, for example, the blenny gives birth to up to 300 young, and the Norwegian morulka (Blenniidae) even up to 1000.

We have cited a number of cases when fertilized eggs are not left to the mercy of fate and the fish show, in one form or another, care for them and the developing juveniles. Such concern is characteristic of an insignificant minority of species. The main, most characteristic type of fish reproduction is one in which the eggs are fertilized outside the mother's body and subsequently the parents leave them to their fate. It is this that explains the enormous fertility of fish, which ensures the preservation of species even with a very large, inevitable under the indicated conditions, death of eggs and juveniles.

Height and age

The lifespan of fish varies greatly. There are species that live a little over a year: some gobies (Gobiidae) and glowing anchovies (Scopelidae). On the other hand, the beluga lives up to 100 years or more. However, due to intensive fishing, the real life expectancy is measured in a few tens of years. Some flounders live for 50-60 years. In all these cases, the ultimate potential life span is meant. In conditions of regular fishing, the actual life expectancy is much shorter.

Unlike most vertebrates, as a rule, fish growth does not stop after reaching sexual maturity, but continues for most of its life, until old age. Along with the above, fish are characterized by a clearly expressed seasonal periodicity of growth. In summer, especially during the feeding period, they grow much faster than in the winter with little food. This uneven growth affects the structure of a number of bones and scales. Periods of stunted growth are imprinted on the skeleton in
in the form of narrow stripes or rings, consisting of small cells. When viewed in incident light, they appear light, in transmitted light, on the contrary, dark. During periods of increased growth, wide rings or layers are deposited, which appear light in transmitted light. The combination of two rings - narrow for winter and wide for summer - represents the year mark. Counting these marks allows you to determine the age of the fish.

Determination of age is made by scales and some parts of the skeleton.

So, according to the scales, you can establish the number of years lived in salmon, herring, carp, cod. The scales are washed in a weak solution of ammonia and viewed between two glass slides under a microscope and a magnifying glass. In perch, burbot, and some other fish, age is established by flat bones, for example, by the operculum and cleitrum. In flounders and cod fish, otoliths serve for this purpose, which are preliminarily defatted and sometimes polished.

The age of sturgeons, catfish and some sharks is established by examining the cross section of the fin ray: in sharks - unpaired, in sturgeons - pectoral.

Determining the age of fish is of great theoretical and practical importance. With a rationally set fishery, the analysis of the age composition of the catch is the most important criterion for establishing overfishing or underfishing. An increase in the body density of younger ages and a decrease in older ones indicates the intensity of fishing and the threat of overfishing. On the contrary, a large percentage of older fish indicate an incomplete use of fish stocks. “So, for example, if in the catch of the vobla (Rutilus rutilus caspius) a large number of seven- and eight-year-old individuals will indicate, as a rule, undershooting (the vobla usually becomes sexually mature upon reaching the age of three), then the presence of sturgeon (Acipenser gtildenstadti) in the catch mainly at the age of 7-8 years will indicate the catastrophic situation of the fishery (sturgeon becomes sexually mature not earlier than 8-10 years of age), since immature individuals predominate in the studied sturgeon catch ”(Nikolsky, 1944). In addition, by comparing the age and size of fish, important conclusions can be drawn about their growth rates, which are often associated with the feeding capacity of water bodies.

Rice. The shape of the fish scales. a - placoid; b - ganoid; c - cycloid; d - ctenoid

Plakoid - the most ancient, preserved in cartilaginous fishes (sharks, rays). Consists of a plate on which a spine rises. Old scales are discarded, new ones appear in their place. Ganoid - predominantly in fossil fish. The scales are rhombic in shape, closely articulated with one another, so that the body is enclosed in a shell. The scales do not change over time. The scales owe their name to ganoin (dentin-like substance), a thick layer lying on the bone plate. Among modern fish, it has shell pikes and mnogopers. In addition, it is present in sturgeons in the form of plates on the upper lobe of the caudal fin (fulcra) and beetles scattered over the body (a modification of several merged ganoid scales).
Gradually changing, the scales lost ganoin. In modern bony fish, it no longer exists, and the scales consist of bony plates (bony scales). These scales can be cycloid - rounded, with smooth edges (carp) and ctenoid with a serrated posterior edge (perch). Both forms are related, but the cycloid, as a more primitive one, is found in low-organized fish. There are cases when, within the same species, males have ctenoid, and females have cycloid scales (flounders of the genus Liopsetta), or even one individual has scales of both forms.
The sizes and thickness of scales in fish vary greatly - from microscopic scales of an ordinary eel to very large, the size of the palm of a scale of a three-meter barbel living in Indian rivers. Few fish have no scales. In some, it has merged into a solid immovable shell, like a box, or formed rows of closely connected bone plates, like in seahorses.
Bony scales, like ganoid ones, are constant, do not change and only increase annually in accordance with the growth of the fish, and distinct annual and seasonal marks remain on them. The winter layer has more frequent and thinner layers than the summer one, therefore it is darker than the summer one. The age of some fish can be determined by the number of summer and winter layers on the scales.
Many fish have silvery guanine crystals under their scales. Washed from the scales, they are a valuable substance for producing artificial pearls. Glue is made from fish scales.
On the sides of the body of many fish, you can see a series of prominent scales with holes that form a lateral line - one of the most important sensory organs. The number of scales in the lateral line -
In the unicellular glands of the skin, pheromones are formed - volatile (odorous) substances released into the environment and affecting the receptors of other fish. They are specific to different species, even closely related ones; in some cases, their intraspecific differentiation (age, sex) was determined.
In many fish, including cyprinids, the so-called fear substance (ichthyopterin) is formed, which is released into the water from the body of a wounded individual and is perceived by its relatives as a signal that warns of danger.
Fish skin regenerates quickly. Through it, on the one hand, a partial release of the final metabolic products occurs, and on the other, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play a large role in life). The skin also plays an important role as a receptor surface: thermo-, baro-, chemo- and other receptors are located in it.
In the thickness of the corium, the integumentary bones of the skull and the girdle of the pectoral fins are formed.
Through the muscle fibers of the myomers, connected to its inner surface, the skin participates in the work of the trunk-tail muscles.

Muscular system and electrical organs

The muscular system of fish, like other vertebrates, is divided into the muscular system of the body (somatic) and internal organs (visceral).

In the first, the muscles of the trunk, head and fins are distinguished. Internal organs have their own muscles.
The muscular system is interconnected with the skeleton (support during contraction) and the nervous system (a nerve fiber approaches each muscle fiber, and each muscle is innervated by a specific nerve). Nerves, blood and lymphatic vessels are located in the connective tissue layer of muscles, which, unlike the muscles of mammals, is small,
In fish, like other vertebrates, the trunk muscles are most developed. It provides swimming for the fish. In real fish, it is represented by two large strands located along the body from head to tail (large lateral muscle - m. Lateralis magnus) (Fig. 1). The longitudinal connective tissue layer divides this muscle into dorsal (upper) and abdominal (lower) parts.

Rice. 1 Musculature of bony fish (according to Kuznetsov, Chernov, 1972):

1 - myomeres, 2 - myosepts

The lateral muscles are divided by myosepts into myomeres, the number of which corresponds to the number of vertebrae. Myomeres are most clearly visible in fish larvae, while their bodies are transparent.
The muscles of the right and left sides, contracting alternately, bend the tail section of the body and change the position of the tail fin, so that the body moves forward.
Above the large lateral muscle along the body between the shoulder girdle and the tail in sturgeons and teleosts lies the straight lateral superficial muscle (m. Rectus lateralis, m. Lateralis superficialis). In salmon, a lot of fat is deposited in it. The rectus abdominal muscle (m. Rectus abdominalis) stretches along the lower side of the body; some fish, such as eels, do not have it. Oblique muscles (m. Obliguus) are located between it and the rectus lateral superficial muscle.
Muscle groups of the head control the movements of the jaw and branchial apparatus (visceral muscles). Fins have their own muscles.
The greatest accumulation of muscles also determines the location of the center of gravity of the body: in most fish, it is located in the dorsal part.
The activity of the trunk muscles is regulated by the spinal cord and cerebellum, and the visceral muscles are innervated by the peripheral nervous system, which is involuntarily excited.

Distinguish between striated (acting largely voluntarily) and smooth muscles (which act independently of the will of the animal). Striated muscles include the skeletal muscles of the body (trunk) and the muscles of the heart. The trunk muscles can contract quickly and strongly, but they soon tire. A feature of the structure of the heart muscles is not the parallel arrangement of isolated fibers, but the branching of their ends and the transition from one bundle to another, which determines the continuous work of this organ.
Smooth muscles also consist of fibers, but much shorter and do not show transverse striation. These are muscles of internal organs and walls of blood vessels, which have peripheral (sympathetic) innervation.
Cross-striped fibers, and therefore muscles, are divided into red and white, differing, as the name suggests, in color. The color is due to the presence of myoglobin, a protein that easily binds oxygen. Myoglobin provides respiratory phosphorylation, accompanied by the release of a large amount of energy.
Red and white fibers differ in a number of morphophysiological characteristics: color, shape, mechanical and biochemical properties (respiration rate, glycogen content, etc.).
The fibers of the red muscle (m. Lateralis superficialis) are narrow, thin, intensively supplied with blood, located more superficially (in most species under the skin, along the body from head to tail), contain more myoglobin in the sarcoplasm;
they contain accumulations of fat and glycogen. Their excitability is less, individual contractions last longer, but proceed more slowly; oxidative, phosphorus and carbohydrate metabolism is more intense than in whites.
In the heart muscle (red) there is little glycogen and a lot of enzymes of aerobic metabolism (oxidative metabolism). It is characterized by a moderate rate of contraction and fatigue more slowly than the white muscles.
In wide, thicker, light white fibers m. lateralis magnus myoglobin is small, they have less glycogen and respiratory enzymes. Carbohydrate metabolism is predominantly anaerobic, and the amount of energy released is less. Individual cuts are quick. Muscles contract and tire faster than red muscles. They lie deeper.
The red muscles are constantly active. They provide long-term and continuous work of organs, maintain constant movement of the pectoral fins, provide body bends when swimming and turning, and continuous work of the heart.
With fast movement, throws, white muscles are active, with slow movements, red ones. Therefore, the presence of red or white fibers (muscles) depends on the mobility of the fish: "sprinters" have almost exclusively white muscles; in fish, which are characterized by prolonged migrations, in addition to the red lateral muscles, there are additional red fibers in the white muscles.
The main mass of muscle tissue in fish is white muscles. For example, in asp, roach, sabrefish, they account for 96.3; 95.2 and 94.9%, respectively.
White and red muscles differ in chemical composition. Red muscle contains more fat, while white muscle contains more moisture and protein.
The thickness (diameter) of the muscle fiber varies depending on the type of fish, their age, size, lifestyle, and in pond fish - on the conditions of keeping. For example, in carp grown on natural food, the diameter of the muscle fiber is (μm): in fry - 5 ... 19, underyearlings - 14 ... 41, two-year-olds - 25 ... 50.
The trunk muscles form the bulk of fish meat. The meat yield as a percentage of the total body weight (meatiness) is not the same in different species, and in individuals of the same species it differs depending on gender, conditions of detention, etc.
Fish meat is digested faster than the meat of warm-blooded animals. It is often colorless (pike perch) or has shades (orange in salmon, yellowish in sturgeon, etc.), depending on the presence of various fats and carotenoids.
The bulk of the proteins of fish muscles are albumin and globulins (85%); in total, 4 ... 7 protein fractions are isolated in different fish.
The chemical composition of meat (water, fats, proteins, minerals) is different not only in different species, but also in different parts of the body. In fish of one species, the amount and chemical composition of meat depends on the nutritional conditions and physiological state of the fish.
During the spawning period, especially in anadromous fish, reserve substances are consumed, depletion is observed and, as a result, the amount of fat decreases and the quality of meat deteriorates. In chum salmon, for example, during the approach to spawning grounds, the relative mass of bones increases by 1.5 times, skin - by 2.5 times. Muscles are hydrated - the dry matter content is more than halved; fat and nitrogenous substances practically disappear from the muscles - the fish loses up to 98.4% fat and 57% protein.
Features of the environment (primarily food and water) can greatly change the nutritional value of fish: in swampy, muddy or oil-polluted reservoirs, fish have meat with an unpleasant odor. The quality of the meat also depends on the diameter of the muscle fiber, as well as the amount of fat in the muscles. To a large extent, it is determined by the ratio of the mass of muscle and connective tissues, by which it is possible to judge the content of high-grade muscle proteins in the muscles (in comparison with the defective proteins of the connective tissue layer). This ratio changes depending on the physiological state of the fish and environmental factors. In the muscle proteins of teleost fish, proteins account for: sarcoplasma 20 ... 30%, myofibrils - 60 ... 70, stroma - about 2%.
All the variety of body movements ensures the work of the muscular system. It mainly provides both heat and electricity in the body of the fish. An electric current is generated when a nerve impulse is conducted along a nerve, during contraction of myofibrils, irritation of light-sensitive cells, mechanochemoreceptors, etc.
Electrical organs

Anadromous fish. Widespread off the coast of Europe. Mediterranean coast from Gibraltar to Scandinavia, in the western part of the Baltic Sea, including the coast of the Kaliningrad region (Svetovidov, 1973; Hoestlandt, 1991). It is rare in the waters of Russia. There are no subspecies. The taxon, originally described as Alosa alosa bulgarica from the southwestern Black Sea (Svetovidov, 1952), is now considered A. caspia bulgarica (Marinov, 1964; Svetovidov, 1973). The Macedonian subspecies A. alosa macedónica (Svetovidov, 1973) is now distinguished as a separate species, Alosa macedónica Vinciguerra, 1921 (Economidis, 1974; Hoestlandt, 1991). Included in the IUCN Red List. It is an object of fishing. [...]

Anadromous fish, in contrast to non-anadromous fish, should be able to easily switch from the “freshwater” way of osmo, regulation to “sea” when moving from fresh water to sea, and vice versa, when moving in the opposite direction. [...]

Anadromous fish dramatically change their habitat (marine environment to freshwater and vice versa), overcome huge distances (salmon travels 1100-2500 km at a speed of 50-100 km per day), overcome significant rapids, waterfalls. [...]

Anadromous fish. They move for spawning (spawning) either from sea water to fresh water (salmon, herring, sturgeon), or from fresh water to sea water (eels, etc.). [...]

Anadromous and freshwater species. Inhabits the basins of the Barents, White, Baltic, Black, Caspian and Aral seas. 6 subspecies were noted, of which 4 anadromous and 1 lake species live in the waters of Russia. Anadromous fish of Northern Europe, in Russia in the basins of the Baltic, White and Barents Seas up to Pechora. Freshwater river (trout) and lake (brown trout) forms are widespread throughout the basins of these seas. Fishing and fish breeding facility. Baltic populations are sharply decreasing in numbers. It is planned to be entered in the "Red Book of Russia". [...]

Anadromous fish of the salmon family. In an adult state, it reaches a length of up to 60 cm and a weight of up to 6 kg. Inhabits the shores of the Far Eastern seas. Spawns in the rivers of Japan and the Kuril Islands, Primorye and Sakhalin. It is an important fishing object. [...]

Anadromous fish of the Black and Azov Seas. Enters the rivers (Don, Dnieper, Danube delta). The species and its intraspecific forms require additional research. Bänärescu (1964) distinguishes two subspecies from the north-central part of the Black Sea: A. p. borystenis Pavlov, 1954 and A. p. issattschenkov Pavlov, 1959, but does not describe them. Valuable commercial species. It is included in the IUCN Red List under the DD category (IUCN Red list ..., 1996). [...]

In anadromous fish moving from rivers to seas and back for spawning, osmotic pressure undergoes changes, albeit insignificant. During the transition from seawater to freshwater in these fish, an almost complete cessation of water intake through the intestine occurs as a result of degeneration of its mucous membranes (see below, the chapter on migrations). [...]

Many anadromous fish and cyclostomes feed in the sea and enter rivers for breeding, making anadromous migrations. Anadromous migrations are characteristic of lampreys, sturgeons, salmon, some herring, carp and others. Some anadromous fish feed in rivers, and for spawning they go into the sea, making mtadromic migrations - such is the eel, etc. [...]

Salmon is an anadromous fish. Juveniles live in fresh water for 2 to 5 years, eat insects, then slide into the sea and become a predatory fish. Salmon usually feeds on the Baltic Sea. Some of the juveniles remain in the Gulf of Bothnia and Finland. For example, in the Soviet Union, artificially bred salmon does not leave the waters of the Gulf of Finland. For two years in the sea, salmon reaches 3-5 kilograms. It feeds mainly on herring, sprat, gerbil. After reaching puberty, the salmon goes to the river where it was born. The river, the place of his spawning ground, he finds by the smell of water. [...]

Berg LS Fish of the USSR and neighboring countries. Berg LS Spring and winter races in anadromous fish, "Essays on general questions of ichthyology". Iad-vo AN SSSR, 1953, p. 242-260. [...]

Lamprey is an anadromous fish, found in the lower Volga and in the delta channels, even in its coastal part. It is currently very few in number. Leads a hidden lifestyle. Spawns from March to May in strong currents in places with rocky or sandy shoals or in pits. The first larvae appear in May. Like adults, they lead a hidden lifestyle, burrowing in silt or sand. They are caught very rarely. [...]

The movement of anadromous fish, mainly of the Northern Hemisphere (salmon, sturgeon, etc.) from the seas to the rivers for spawning. [...]

L. S. Berg. Fish of fresh waters of Russia. Ts. 2 p. II and-d. Definitive tables of marine and anadromous fish of Europe. [...]

Sevruga is an anadromous fish that lives in the basins of the Caspian, Azov and Black seas. For spawning it goes to the rivers Ural, Volga, Kura, etc. It is a numerous valuable commercial fish, reaching a length of about 2.2 m and a weight of 6-8 kg (average commercial weight of 7-8 kg). Sevruga females reach sexual maturity at 12-17 years old, males at 9-12 years old. Fecundity of females is 20-400 thousand eggs. Spawning takes place from May to August. Duration of incubation of eggs at 23 ° С is about 2-3 days. Juveniles slide into the sea at the age of 2-3 months. [...]

Caspian anadromous fish spawn in the rivers Volga, Ural »Kura. But the Volga and Kura are regulated by cascades of waterworks and many spawning grounds were inaccessible to fish. Only the lower reaches of the river. The Urals were left free from the construction of waterworks to preserve spawning migrations of fish and their natural reproduction. Currently, the reduction in the natural reproduction of fish products is partially offset by artificial fish farming. [...]

Commercial fish of the sturgeon family, widespread in the basins of the Aral, Caspian and Black seas. The thorn is an anadromous fish, it enters the rivers for spawning, there are also “resident” forms of the thorn ”for several years that do not leave the river“ probably ”before the onset of puberty. [...]

During migration along the river, most fish usually stop feeding or feed less intensively than in the sea, and the huge expenditure of energy, naturally, requires the consumption of nutrients accumulated during feeding in the sea. This is why most anadromous fish are severely emaciated as they move upstream. [...]

As a rule, fish have permanent places of feeding ("fattening"). Some fish constantly live, breed and winter in areas with abundant food, others make significant movements to feeding grounds (forage migrations), spawning (spawning migrations) or to wintering grounds (wintering migrations). In accordance with this, fish are divided into sedentary (or tundra), anadromous and semi-anadromous. Anadromous fish make long journeys either from the seas, where they spend most of their lives, to spawning grounds in rivers (chum salmon, whitefish, nelma), or from the rivers in which they live, go to the sea (eel). [. ..]

However, the presence of anadromous fish in the subtropics, tropics, and the equatorial zone indicates that salting in itself did not cause an anadromous lifestyle. The transition of sea or river fish to anadromous mode, life could develop even with a relatively stable regime of river flow, into which anadromous fish enter for reproduction. [...]

Fish hatcheries are of great importance for the protection of a number of anadromous fish. At such factories, usually built at the mouths of large rivers or near dams, producers are caught, artificial insemination is carried out. The larvae of fish obtained from caviar are kept in nursery ponds, and then the grown juveniles are released into rivers or reservoirs. In Russia, billions of juveniles are raised annually in such farms, which is of great importance in the reproduction and restoration of valuable fish species: sturgeon, salmon, some whitefish and other anadromous and some semi-anadromous fish, such as pike perch. [...]

In addition to these institutes, basin research institutes of fisheries conduct research in each fishery basin. The All-Union Scientific Research Institute of Pond Fisheries (VNIIPRKh), which is part of the All-Union Scientific and Production Association for Fish Farming (VNPO for Fish Farming), UkrNIIRKh and other scientific organizations in many Union republics, is conducting research on inland water bodies. [...]

Kutum (Rutilus frissi kutum Kamensky) is an anadromous fish in the southwestern region of the Caspian basin. Acclimatized in the basin of the Black and Azov Seas. A related form - carp (R. frissi Nordm.) Was known in the rivers of the northwestern part of the Black Sea, now it is found only in the r. Southern Bug.[ ...]

Mass tagging and tracking of fish carrying ultrasonic transmitters has shown that the lower and upper spawning grounds are used by the producers of one local stock, during the feeding and wintering periods, not leaving its range. The approach to spawning grounds is carried out either in autumn (winter fish) or in spring (spring fish). The stereotype of the behavior of spawners going to spawn in the river does not differ from that described for typical anadromous fish. [...]

Winter migrations are expressed both in anadromous and semi-anadromous fish, as well as in marine and freshwater fish. In anadromous fish, wintering migration is often the beginning of spawning. Winter forms of anadromous fish move from feeding grounds to the sea for wintering in rivers, where they concentrate in deep pits and hibernate in a sedentary state, usually without feeding. Winter migrations take place among anadromous fish among sturgeons, Atlantic salmon, Aral barbel and some others. Wintering migrations are well expressed in many semi-anadromous fish. In the North Caspian, Aral and Azov Seas, adult vobla, ram, bream, pike perch and some other semi-anadromous fish, after the end of the feeding period, move to the lower reaches of the rivers to wintering grounds. [...]

A decrease in the stocks of some commercial fish (salmon, sturgeon, herring, some cyprinids, etc.) and especially a change in the hydrological regime of large rivers (Volga, Kura, Dnieper, etc.) force researchers to work intensively on fish reproduction. Hydroelectric construction on rivers causes such great disturbances in their regimes that many anadromous fish cannot use old spawning grounds in rivers. The lack of proper external conditions excludes the reproduction of anadromous fish. [...]

At the same time, acclimatized fish species appeared: sabrefish, white-eyed, carp, silver carp, sleeper, eel, guppies, etc. Now the ichthyofauna of the r. Moscow has 37 species [Sokolov et al., 2000]. Anadromous fish have completely disappeared, as well as fish species that need conditions of rivers with a fast current. More numerous are fish resistant to eutrophication - inhabitants of stagnant or weak-flowing waters. [...]

Anadromous fish, such as sturgeon, salmon, whitefish, and carp, have become the main objects of breeding at fish hatcheries. In spawning and nursery farms and fish hatcheries, semi-anadromous and tundra fish are bred: cyprinids, perches, etc. [...]

The most important method of increasing the productivity of commercial fish stocks is to catch fish when it is in the most marketable condition. In most fish, their fat content and fatness varies greatly from season to season. This is especially pronounced in anadromous fish that make large migrations without food consumption, as well as in fish that have a break in feeding during wintering. [...]

In our country, work on the acclimatization of fish is being widely developed. The incentive for such measures is the growing need for the production of commercial fish. In order to acclimatize, the ichthyofauna of some reservoirs (lakes Sevan, Balkhash, the Aral Sea) is reconstructed due to the introduction of valuable fish species, newly created reservoirs (reservoirs) are populated with new fish species, etc. slow flow. We are convinced that almost all anadromous fish (living in sea and fresh water) can be transferred to fresh water - to ponds. [...]

Anadromous fish such as herring, salmon, sturgeon, carp rush hundreds and thousands of kilometers up the river every year. [...]

The fourth type of migration cycles is characteristic of a number of local populations of anadromous fish in lakes and reservoirs that have mastered reproductive biotopes in rivers flowing from a feeding reservoir. These fish make pre-spawning migration downstream of the river, and after spawning, they return to the lake feeding biotopes, where they live until the next spawning period. In local herds, groups of winter individuals were also found here, leaving for the area of ​​spawning grounds in autumn, that is, making winter-spawning migration. [...]

All salmonids, both of the genus Salmo and the genus Oncorhynchus, are autumn spawning fish (for an exception, see above for the Gogchin trout). None of them breed in seawater; for spawning, all salmon enter rivers: salty water, even in small quantities, is fatal to sperm and eggs, thus preventing their fertilization. Some of the salmon - salmon, anadromous kundzha, Salmo trutta L. and the Caspian and Aral salmon and all Far Eastern salmon - are typical anadromous fish that live in the marine environment and enter rivers only for breeding purposes, others are lake kundzha (Salmo trutta lacustris) , the brook forms of Salmo trutta and its subspecies, which form the morphs of trout, are water-borne and live in a fresh environment all the time, only making small movements from feeding grounds to spawning grounds. In some cases, and typical anadromous fish form or have formed in the past forms that constantly live in fresh water. To which belong: Salmo salar morpha relictus (Malmgren) -grain salmon, lacustrine forms Oncorhynchus nerka, river form Salmo (Oncorhynchus) masu. All these freshwater morphs differ from their marine relatives in smaller size and slower growth rates. This is already the effect of fresh water, as we will see below, on typical anadromous salmon, since they have to live in fresh water. [...]

The adaptive value of dwarf, constantly living in rivers, males in anadromous fish is to provide a population of greater numbers and greater reproductive capacity with a smaller food base than if the males were large, anadromous. [...]

The physiological features of the migratory state are best studied in anadromous fish using the example of (Yshdromny spawning migrations. In these fish, as well as in lampreys, the stimulus to spawning migration arises after a long (from 1 to 15-16 years) period of marine life. different seasons and with different conditions of the reproductive system. An example is the so-called spring and winter races of fish and cyclostomes. The most common indicator that stimulates migration in fish is high fat content. As you approach spawning grounds, fat reserves decrease, which reflects a high level of energy consumption on the movement and maturation of reproductive products.And in this case, there are differences between the spring and winter races: in the spring, entering the rivers in spring, shortly before spawning, fat content is not very high. [...]

A subvariant of type III migrations are displacements. winter ecological groups of local stocks of anadromous fish "breeding in the spring, but entering the rivers in the areas of reproductive biotopes in the fall of the previous year. [...]

The method is also widespread, when commercial fish spawn in artificial reservoirs, juveniles are reared to the stage of downstream migration and then released into natural reservoirs. In this way, artificial reproduction of semi-anadromous commercial fish is built, such as mackerel, carp, etc., in fish farms in the Volga delta, the lower reaches of the Don, Kuban and a number of other rivers. Also, an important form of fish farming is one in which a person conducts the entire process from the moment of receiving mature productive eggs and milk from producers, fertilization of eggs, their incubation to the release of viable fry from a fish hatchery into a natural reservoir. Thus, breeding is carried out, mainly, of anadromous fish - sturgeon, for example, on the Kura, salmon in the north and the Far East, whitefish and some others (Cherfas, 1956). With this type of breeding, it is often necessary to hold the producers until the gonads mature, and sometimes stimulate the return of the gonads by injecting the pituitary hormone. The incubation of eggs is carried out in special fish-breeding devices installed in a special room or exposed in the river bed. Juveniles are usually reared to a downward state in special pools or ponds. At the same time, juveniles are fed with artificial or natural feed. Many fish hatcheries have special workshops for the cultivation of live feed - crustaceans, small-bristled worms, bloodworms. The efficiency of the fish hatchery operation is determined by the longevity of the fry released from the hatchery, that is, the value of the commercial return. Naturally, the higher the applied fish farming biotechnology, the higher it is. efficiency.[ ...]

The first step towards solving this issue is a delay in the duration of the freshwater lifestyle of anadromous fish. With regard to sturgeon fish (sturgeon, stellate sturgeon and beluga), this has already been successfully carried out. The second and most difficult step is managing the breeding process. [...]

Daily food intake also depends on age: juveniles usually eat more than adults and older fish. In the pre-spawning period, the intensity of feeding decreases, and many marine and especially anadromous fish feed little or completely stop feeding. The daily feeding rhythm also differs in different fish. In peaceful fish, especially planktivorous, food interruptions are small, while in predators they can last more than a day. Cyprinids have two maxima of feeding activity: in the morning and in the evening. [...]

In the same area, the entire life cycle of vendace and smelt takes place, which in their migrations, with the exception of 4cucherechenskaya, do not go beyond the delta. Their spawning takes place in tundra rivers connected with the lips and river deltas. Part of the vendace spawns directly in the bays of the lip (New Port area). Among other fish, ruff and burbot deserve attention, the reserves of which are underutilized. [...]

Undoubtedly, the temperature regime is the leading factor determining the normal course of maturation of fish reproductive products, the beginning and duration of spawning, and its effectiveness. However, under natural conditions, for the successful reproduction of most freshwater and anadromous fish, the hydrological regime is also important, or rather, the optimal combination of temperature and level regimes of the reservoir. It is known that spawning of many fish begins with an intense rise in water and, as a rule, coincides with the peak of the flood. Meanwhile, the regulation of the flow of many rivers has dramatically changed their hydrological regime and the usual ecological conditions for the reproduction of fish, both those who are forced to live in the reservoirs themselves, and those that remained in the downstream of the waterworks. [...]

It should be noted that the herds or ecological races into which a subspecies breaks down often have different breeding sites. In semi-anadromous and anadromous fish, so-called seasonal races and biological groups are formed, which have a similar biological significance. But in this case (in herds and races), the "sequence" of reproduction is provided even more by the fact that it is fixed hereditarily. [...]

An almost extinct species, previously widespread along the entire coast of Europe (Berg, 1948; Holöik, 1989). In the north, it was found up to Murman (Lagunov, Konstantinov, 1954). Anadromous fish. In the Ladoga and Onega lakes, there may have been a living form (Berg, 1948; Podushka, 1985; Kuderskiy, 1983). A very valuable species, at the end of the 19th - beginning of the 20th centuries, which had commercial value. It is included in the "Red Data Books" of the IUCN, USSR, among the specially protected fish of Europe (Pavlov et al., 1994) and is scheduled to be included in the "Red Data Book of Russia". [...]

The impact of hydropower on the conditions for reproduction of fish stocks is one of the most actively discussed issues in the environmental problem. The annual fish catch in the former USSR reached 10 million tons, of which about 90% was caught in the open seas, and only J% of the catch relates to inland basins. But in inland seas, rivers, lakes and reservoirs, about 90% of the world's most valuable fish species - sturgeon and more than 60% - salmon are reproduced, which makes the inland water bodies of the country especially important for fish farming. The negative impact of hydroelectric power plants on fisheries is manifested in violations of the natural migration routes of anadromous fish (sturgeon, salmon, whitefish) to spawning grounds and a sharp decrease in flood water discharge, which does not provide watering of the spawning grounds of semi-anadromous fish in the lower reaches of rivers (carp, pike perch, bream) ... The reduction of fish stocks in inland waters is also influenced by the pollution of water basins by discharges of oil products and effluents from industrial enterprises, timber rafting, water transport, discharges of fertilizers and chemical pest control agents. [...]

First of all, due to the elementary populations, the population of a given herd is of different quality. Imagine that, for example, a vobla in the North Caspian Sea or other semi-anadromous or anadromous fish would not have such a varied quality, but, say, all fish would ripen at the same time and therefore all would immediately rush to the Volga delta for spawning. In this case, there would be overpopulation at the spawning grounds and the death of spawners due to lack of oxygen. But there is no such overpopulation and cannot be, since in reality the spawning passage is sufficiently extended and the fish can alternately use limited breeding sites, ensuring the continuation of the life of a given subspecies or herd. [...]

Pasture fish farming has large reserves, based on obtaining marketable products by improving and productive use of the natural food base of lakes, rivers, reservoirs, acclimatization of fish and directed formation of ichthyofauna, artificial breeding and rearing of juveniles of anadromous fish (sturgeon, salmon) to restore their stocks. [...]

Intensive human activity associated with the development of industry, agriculture, water transport, etc. in a number of cases adversely affected the state of fishery reservoirs. Almost all the largest rivers of our country: Volga, Kama, Ural, Don, Kuban, Dnieper, Dniester, Daugava, Angara, Yenisei, Irtysh, Syrdarya, Amu Darya, Kura, etc. are partially or completely regulated by dams of large hydroelectric power plants or irrigation hydroelectric facilities. Almost all anadromous fish - sturgeon, salmon, whitefish, carp, herring - and semi-anadromous - perch, carp, etc. - have lost their natural spawning grounds that have developed over centuries. [...]

Salt composition of water. The salt composition of water is understood as the totality of mineral and organic compounds dissolved in it. Depending on the amount of dissolved salts, fresh water is distinguished (up to 0.5% o) (% o - ppm - salt content in g / l of water), brackish (0.5-16.0% o), sea (16-47 % o) and salted (more than 47% o). Sea water contains mainly chlorides, while fresh water contains carbonates and sulfates. Therefore, fresh water is hard and soft. Too freshened, as well as oversalted, reservoirs are unproductive. Salinity of water is one of the main factors that determine the habitat of fish. Some fish live only in fresh water (freshwater), others in sea (sea). Anadromous fish change seawater to fresh water and vice versa. Salinization or desalination of waters is usually accompanied by a change in the composition of the ichthyofauna, food base, and often leads to a change in the entire biocenosis of the reservoir.

The structure and physiological characteristics of fish

Heading

Body shape and ways of movement

Skin of fish

Digestive system

Respiratory system and gas exchange (New)

Circulatory system

Nervous system and senses

Endocrine glands

Poisonousness and venomousness of fish

The shape of the body of fish and the ways of movement of fish

The shape of the body should provide the fish with the ability to move in water (an environment much denser than air) with the least energy expenditure and at a speed corresponding to its vital needs.
The shape of the body that meets these requirements has developed in fish as a result of evolution: a smooth, without protrusions body, covered with mucus, facilitates movement; no neck; a pointed head with compressed gill covers and compressed jaws cuts the water; the fin system detects movement in the desired direction. According to lifestyle, up to 12 different types of body shape are highlighted

Rice. 1 - garfish; 2 - mackerel; 3 - bream; 4 - moon fish; 5 - flounder; 6 - eel; 7 - needle fish; 8 - herring king; 9 - slope; 10 - hedgehog fish; 11 - box; 12 - grenadier.

Sagittal - the bones of the snout are elongated and pointed, the body of the fish along the entire length has the same height, the dorsal fin is referred to the caudal and is located above the anal, which creates an imitation of the plumage of the arrow. This form is typical for fish that do not travel long distances, stay in ambush and develop high speeds for a short period of time due to the push of their fins when throwing at prey or avoiding a predator. These are pikes (Esox), garfish (Belone), etc. Torpedo (it is often called fusiform) - characterized by a pointed head, a rounded body that has an oval shape in cross section, a refined caudal stem, often with additional fins. It is characteristic of good swimmers capable of long movements - tuna, salmon, mackerel, sharks, etc. These fish are capable of swimming for a long time, so to speak, with a cruising speed of 18 km per hour. Salmon are capable of making two to three meter jumps when overcoming obstacles during spawning migrations. The maximum speed that a fish can develop is 100-130 km per hour. This record belongs to the sailfish. The body, symmetrically compressed from the sides, is strongly compressed from the sides, high with a relatively short length and high. These are fishes of coral reefs - bristletooths (Chaetodon), thickets of bottom vegetation - scalars (Pterophyllum). This body shape helps them to easily maneuver among obstacles. Some pelagic fish also have a symmetrically compressed laterally compressed body shape, which need to quickly change their position in space to disorient predators. Moonfish (Mola mola L.) and bream (Abramis brama L.) have the same body shape. The body asymmetrically compressed from the sides - the eyes are displaced to one side, which creates an asymmetry of the body. It is characteristic of the bottom sedentary fish of the Flounder order, helping them to camouflage well at the bottom. Wave-like bending of the long dorsal and anal fins plays an important role in the movement of these fish. The body is flattened in the dorsoventral direction - strongly compressed in the dorsal-abdominal direction, as a rule, the pectoral fins are well developed. This body shape is characteristic of sedentary bottom fish - most stingrays (Batomorpha), monkfish (Lophius piscatorius L.). The flattened body masks the fish in the bottom conditions, and the eyes located on top help to see the prey. Eel-like shape - the body of the fish is elongated, rounded, having the form of an oval in cross-section. The dorsal and anal fins are long, there are no pelvic fins, and the caudal fin is small. It is typical for such bottom and bottom fish as Anguilliformes, moving, laterally bending the body. Ribbon-like - the body of the fish is elongated, but unlike the eel-like shape, it is strongly compressed from the sides, which provides a large specific surface area and allows the fish to live in the water column. Their movement pattern is the same as in eel-shaped fish. This body shape is typical for the saber fish (Trichiuridae), the herring king (Regalecus). Macrural - the body of the fish is high in the front part, narrowed from the back, especially in the tail section. The head is large, massive, the eyes are large. It is characteristic of deep-sea sedentary fish - macrurus-like (Macrurus), chimera-like (Chimaeriformes). Asterolepid (or box-like) - the body is enclosed in a bony shell, which provides protection from predators. This body shape is characteristic of bottom dwellers, many of which are found in coral reefs, for example for box bodies (Ostracion). The spherical shape is characteristic of some species from the order Pufferfish (Tetraodontiformes) - the ball fish (Sphaeroides), the hedgehog fish (Diodon), etc. These fish are poor swimmers and move with the help of undulating (undulating) movements of the fins over short distances. In case of danger, fish inflate the intestinal air sacs, filling them with water or air; at the same time, the thorns and thorns on the body are straightened, protecting them from predators. The needle-shaped body is characteristic of the sea needles (Syngnathus). Their elongated body, hidden in the bony shell, imitates the leaves of the zostera, in the thickets of which they live. Fish are deprived of lateral mobility and move with the help of undulating (undulating) action of the dorsal fin.
Often there are fish whose body shape simultaneously resembles different types of forms. To eliminate the unmasking shadow on the belly of a fish that appears when illuminated from above, small pelagic fish, for example, herring (Clupeidae), sabrefish (Pelecus cultratus (L.)], have a pointed, laterally compressed abdomen with a sharp keel. mackerel (Scomber), swordfish (Xiphias gladius L.), tunas (Thunnus) usually do not develop keels. Their method of protection consists in speed of movement, not in camouflage. with a large base downward, which excludes the appearance of shadows on the sides when illuminated from above.Therefore, most bottom fish have a wide flattened body.

SKIN, SCALES AND LUMINOUS BODIES

Rice. The shape of the fish scales. a - placoid; b - ganoid; c - cycloid; d - ctenoid

Plakoid - the most ancient, preserved in cartilaginous fishes (sharks, rays). Consists of a plate on which a spine rises. Old scales are discarded, new ones appear in their place. Ganoid - predominantly in fossil fish. The scales are rhombic in shape, closely articulated with one another, so that the body is enclosed in a shell. The scales do not change over time. The scales owe their name to ganoin (dentin-like substance), a thick layer lying on the bone plate. Among modern fish, it has shell pikes and mnogopers. In addition, it is present in sturgeons in the form of plates on the upper lobe of the caudal fin (fulcra) and beetles scattered over the body (a modification of several merged ganoid scales).
Gradually changing, the scales lost ganoin. In modern bony fish, it no longer exists, and the scales consist of bony plates (bony scales). These scales can be cycloid - rounded, with smooth edges (carp) and ctenoid with a serrated posterior edge (perch). Both forms are related, but the cycloid, as a more primitive one, is found in low-organized fish. There are cases when, within the same species, males have ctenoid, and females have cycloid scales (flounders of the genus Liopsetta), or even one individual has scales of both forms.
The sizes and thickness of scales in fish vary greatly - from microscopic scales of an ordinary eel to very large, the size of the palm of a scale of a three-meter barbel living in Indian rivers. Few fish have no scales. In some, it has merged into a solid immovable shell, like a box, or formed rows of closely connected bone plates, like in seahorses.
Bony scales, like ganoid ones, are constant, do not change and only increase annually in accordance with the growth of the fish, and distinct annual and seasonal marks remain on them. The winter layer has more frequent and thinner layers than the summer one, therefore it is darker than the summer one. The age of some fish can be determined by the number of summer and winter layers on the scales.
Many fish have silvery guanine crystals under their scales. Washed from the scales, they are a valuable substance for producing artificial pearls. Glue is made from fish scales.
On the sides of the body of many fish, you can see a series of prominent scales with holes that form a lateral line - one of the most important sensory organs. The number of scales in the lateral line -
In the unicellular glands of the skin, pheromones are formed - volatile (odorous) substances released into the environment and affecting the receptors of other fish. They are specific to different species, even closely related ones; in some cases, their intraspecific differentiation (age, sex) was determined.
In many fish, including cyprinids, the so-called fear substance (ichthyopterin) is formed, which is released into the water from the body of a wounded individual and is perceived by its relatives as a signal that warns of danger.
Fish skin regenerates quickly. Through it, on the one hand, a partial release of the final metabolic products occurs, and on the other, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play a large role in life). The skin also plays an important role as a receptor surface: thermo-, baro-, chemo- and other receptors are located in it.
In the thickness of the corium, the integumentary bones of the skull and the girdle of the pectoral fins are formed.
Through the muscle fibers of the myomers, connected to its inner surface, the skin participates in the work of the trunk-tail muscles.

Muscular system and electrical organs

The muscular system of fish, like other vertebrates, is divided into the muscular system of the body (somatic) and internal organs (visceral).

In the first, the muscles of the trunk, head and fins are distinguished. Internal organs have their own muscles.
The muscular system is interconnected with the skeleton (support during contraction) and the nervous system (a nerve fiber approaches each muscle fiber, and each muscle is innervated by a specific nerve). Nerves, blood and lymphatic vessels are located in the connective tissue layer of muscles, which, unlike the muscles of mammals, is small,
In fish, like other vertebrates, the trunk muscles are most developed. It provides swimming for the fish. In real fish, it is represented by two large strands located along the body from head to tail (large lateral muscle - m. Lateralis magnus) (Fig. 1). The longitudinal connective tissue layer divides this muscle into dorsal (upper) and abdominal (lower) parts.

Rice. 1 Musculature of bony fish (according to Kuznetsov, Chernov, 1972):

1 - myomeres, 2 - myosepts

The lateral muscles are divided by myosepts into myomeres, the number of which corresponds to the number of vertebrae. Myomeres are most clearly visible in fish larvae, while their bodies are transparent.
The muscles of the right and left sides, contracting alternately, bend the tail section of the body and change the position of the tail fin, so that the body moves forward.
Above the large lateral muscle along the body between the shoulder girdle and the tail in sturgeons and teleosts lies the straight lateral superficial muscle (m. Rectus lateralis, m. Lateralis superficialis). In salmon, a lot of fat is deposited in it. The rectus abdominal muscle (m. Rectus abdominalis) stretches along the lower side of the body; some fish, such as eels, do not have it. Oblique muscles (m. Obliguus) are located between it and the rectus lateral superficial muscle.
Muscle groups of the head control the movements of the jaw and branchial apparatus (visceral muscles). Fins have their own muscles.
The greatest accumulation of muscles also determines the location of the center of gravity of the body: in most fish, it is located in the dorsal part.
The activity of the trunk muscles is regulated by the spinal cord and cerebellum, and the visceral muscles are innervated by the peripheral nervous system, which is involuntarily excited.

Distinguish between striated (acting largely voluntarily) and smooth muscles (which act independently of the will of the animal). Striated muscles include the skeletal muscles of the body (trunk) and the muscles of the heart. The trunk muscles can contract quickly and strongly, but they soon tire. A feature of the structure of the heart muscles is not the parallel arrangement of isolated fibers, but the branching of their ends and the transition from one bundle to another, which determines the continuous work of this organ.
Smooth muscles also consist of fibers, but much shorter and do not show transverse striation. These are muscles of internal organs and walls of blood vessels, which have peripheral (sympathetic) innervation.
Cross-striped fibers, and therefore muscles, are divided into red and white, differing, as the name suggests, in color. The color is due to the presence of myoglobin, a protein that easily binds oxygen. Myoglobin provides respiratory phosphorylation, accompanied by the release of a large amount of energy.
Red and white fibers differ in a number of morphophysiological characteristics: color, shape, mechanical and biochemical properties (respiration rate, glycogen content, etc.).
The fibers of the red muscle (m. Lateralis superficialis) are narrow, thin, intensively supplied with blood, located more superficially (in most species under the skin, along the body from head to tail), contain more myoglobin in the sarcoplasm;
they contain accumulations of fat and glycogen. Their excitability is less, individual contractions last longer, but proceed more slowly; oxidative, phosphorus and carbohydrate metabolism is more intense than in whites.
In the heart muscle (red) there is little glycogen and a lot of enzymes of aerobic metabolism (oxidative metabolism). It is characterized by a moderate rate of contraction and fatigue more slowly than the white muscles.
In wide, thicker, light white fibers m. lateralis magnus myoglobin is small, they have less glycogen and respiratory enzymes. Carbohydrate metabolism is predominantly anaerobic, and the amount of energy released is less. Individual cuts are quick. Muscles contract and tire faster than red muscles. They lie deeper.
The red muscles are constantly active. They provide long-term and continuous work of organs, maintain constant movement of the pectoral fins, provide body bends when swimming and turning, and continuous work of the heart.
With fast movement, throws, white muscles are active, with slow movements, red ones. Therefore, the presence of red or white fibers (muscles) depends on the mobility of the fish: "sprinters" have almost exclusively white muscles; in fish, which are characterized by prolonged migrations, in addition to the red lateral muscles, there are additional red fibers in the white muscles.
The main mass of muscle tissue in fish is white muscles. For example, in asp, roach, sabrefish, they account for 96.3; 95.2 and 94.9%, respectively.
White and red muscles differ in chemical composition. Red muscle contains more fat, while white muscle contains more moisture and protein.
The thickness (diameter) of the muscle fiber varies depending on the type of fish, their age, size, lifestyle, and in pond fish - on the conditions of keeping. For example, in carp grown on natural food, the diameter of the muscle fiber is (μm): in fry - 5 ... 19, underyearlings - 14 ... 41, two-year-olds - 25 ... 50.
The trunk muscles form the bulk of fish meat. The meat yield as a percentage of the total body weight (meatiness) is not the same in different species, and in individuals of the same species it differs depending on gender, conditions of detention, etc.
Fish meat is digested faster than the meat of warm-blooded animals. It is often colorless (pike perch) or has shades (orange in salmon, yellowish in sturgeon, etc.), depending on the presence of various fats and carotenoids.
The bulk of the proteins of fish muscles are albumin and globulins (85%); in total, 4 ... 7 protein fractions are isolated in different fish.
The chemical composition of meat (water, fats, proteins, minerals) is different not only in different species, but also in different parts of the body. In fish of one species, the amount and chemical composition of meat depends on the nutritional conditions and physiological state of the fish.
During the spawning period, especially in anadromous fish, reserve substances are consumed, depletion is observed and, as a result, the amount of fat decreases and the quality of meat deteriorates. In chum salmon, for example, during the approach to spawning grounds, the relative mass of bones increases by 1.5 times, skin - by 2.5 times. Muscles are hydrated - the dry matter content is more than halved; fat and nitrogenous substances practically disappear from the muscles - the fish loses up to 98.4% fat and 57% protein.
Features of the environment (primarily food and water) can greatly change the nutritional value of fish: in swampy, muddy or oil-polluted reservoirs, fish have meat with an unpleasant odor. The quality of the meat also depends on the diameter of the muscle fiber, as well as the amount of fat in the muscles. To a large extent, it is determined by the ratio of the mass of muscle and connective tissues, by which it is possible to judge the content of high-grade muscle proteins in the muscles (in comparison with the defective proteins of the connective tissue layer). This ratio changes depending on the physiological state of the fish and environmental factors. In the muscle proteins of teleost fish, proteins account for: sarcoplasma 20 ... 30%, myofibrils - 60 ... 70, stroma - about 2%.
All the variety of body movements ensures the work of the muscular system. It mainly provides both heat and electricity in the body of the fish. An electric current is generated when a nerve impulse is conducted along a nerve, during contraction of myofibrils, irritation of light-sensitive cells, mechanochemoreceptors, etc.
Electrical organs

The electrical organs are peculiarly altered muscles. These organs develop from the rudiments of the striated muscles and are located on the sides of the fish body. They consist of many muscle plates (in an electric eel there are about 6,000 of them), converted into electrical plates (electrocytes), interlayered with gelatinous connective tissue. The lower part of the plate is negatively charged, the upper one is positively charged. Discharges occur under the influence of impulses of the medulla oblongata. As a result of discharges, water decomposes into hydrogen and oxygen, therefore, for example, in the frozen water bodies of the tropics, small inhabitants accumulate near electric fish - mollusks, crustaceans, attracted by more favorable breathing conditions.
Electric organs can be located in different parts of the body: for example, in a sea fox stingray - on the tail, in an electric catfish - on the sides.
By generating electric current and perceiving lines of force,
distorted by objects on the way, the fish orient themselves in the stream, detect obstacles or prey from a distance of several meters, even in muddy water.
In accordance with the ability to generate electric fields, fish are divided into three groups:
1. Strongly electrical types - have large electrical organs that generate discharges from 20 to 600 and even 1000 V. The main purpose of the discharges is attack and defense (electric eel, electric ray, electric catfish).
2. Weak electric species - have small electrical organs that generate discharges with a voltage of less than 17 V. The main purpose of the discharges is location, signaling, orientation (many Mormirids, Gymnotids, some stingrays living in the muddy rivers of Africa).
3. Non-electrical species - do not have specialized organs, but have electrical activity. The discharges generated by them spread to 10 ... 15 m in sea water and up to 2 m in fresh water. The main purpose of the generated electricity is location, orientation, signaling (many marine and freshwater fish: for example, horse mackerel, atherina, perch, etc.).

Digestive system

In the digestive tract of real fish, the oral cavity, pharynx, esophagus, stomach, intestines (small, large, rectum, ending with the anus) are distinguished. Sharks, rays and some other fish have a cloaca in front of the anus - an extension into which the rectum and ducts of the urinary and reproductive systems pour out.

There are no salivary glands in the mouth of the fish. The glandular cells of the oral cavity and pharynx secrete mucus, which does not have digestive enzymes and only contributes to the swallowing of food, and also protects the epithelium of the oral cavity with impregnated taste buds (receptors).

Only cyclostomes have a powerful and protruding tongue; in bony fish, it does not have its own muscles.

The mouth is usually equipped with teeth. By the presence of an enamel cap and layers of dentin, they resemble the teeth of higher vertebrates. In predators, they are located both on the jaws and on other bones of the oral cavity, sometimes even on the tongue; they are sharp. often hook-shaped, inclined inward towards the pharynx, and serve to grasp and hold the victim. Many peaceful fish (many herring, carp, etc.) have no teeth on their jaws.

The feeding mechanism is coordinated with the respiratory mechanism. Water sucked into the mouth during inhalation also carries small planktonic organisms, which, when water is pushed out of the gill cavity (exhalation), are retained in it by the gill stamens.

Rice. 1 Gill rakers of planktivorous (a), benthivorous (b), carnivorous (c) fish.

They are so thin, long and numerous in plankton-eating fish (plankton-feeders) that they form a filter apparatus. The strained lump of food is sent to the esophagus. Predatory fish do not need to filter food, their stamens are rare, low, rough, sharp or hooked: they are involved in retaining prey.

Some benthic-eating fish have wide and massive pharyngeal teeth on the posterior branchial arch. They serve to grind food.

The esophagus following the pharynx, usually short, wide and straight with strong muscular walls, carries food into the stomach. The walls of the esophagus contain numerous mucus-secreting cells. In open-bladder fish, the swimbladder duct opens into the esophagus.

Not all fish have stomachs. Carp, many gobies and some others belong to the gastric.

There are glandular cells in the gastric mucosa. producing hydrochloric acid and pepsin, which breaks down protein in an acidic environment, and mucus. Here, predatory fish digest the bulk of their food.

The bile duct and pancreatic duct flow into the initial part of the intestine (small intestine). Through them, bile and pancreatic enzymes enter the intestine, under the influence of which proteins are broken down to amino acids, fats to glycerol and fatty acids, and polysaccharides are broken down to sugars, mainly glucose.

In the intestine, in addition to the breakdown of nutrients, they are absorbed, which proceeds most intensively in the posterior region. This is facilitated by the folded structure of its walls, the presence of villous outgrowths in them, penetrated by capillaries and lymphatic vessels, the presence of cells secreting mucus.

In many species, in the initial part of the intestine, blind processes are placed - pyloric appendages, the number of which varies greatly: from 3 in perch to 400 in salmon

Cyprinids, catfish, pikes and some other fish do not have pyloric appendages. With the help of the pyloric appendages, the absorption surface of the intestine is increased several times.

In fish that do not have a stomach, the intestinal tract is a mostly undifferentiated tube, tapering towards the end. In some fish, in particular carp, the front part of the intestine is enlarged and resembles a stomach. However, this is only an external analogy: there are no pepsin-producing glands characteristic of the stomach.

The structure, shape and length of the digestive tract are varied due to the nature of the food (food items, their digestibility), and the characteristics of digestion. There is a certain dependence of the length of the digestive tract on the type of food. So, the relative length of the intestine (the ratio of the length of the intestine to the length of the body.) Is in herbivores (pinagora and silver carp) - b ... 15, in omnivores (crucian carp and carp) - 2 ... 3, in carnivores (pike, pike perch, perch) - 0.6 ... 1.2.

The liver is a large digestive gland, inferior in size in adult fish only to gonads. Its mass in sharks is 14 ... 25%, in teleosts - 1 ... 8% of body mass. This is a complex tubular-reticular gland, by origin associated with the intestines. In embryos, it is a blind outgrowth.

The bile ducts carry bile into the gallbladder (only a few species do not have it). Bile, due to an alkaline reaction, neutralizes the acidic reaction of gastric juice. It emulsifies fats, activates lipase - an enzyme of the pancreas.

From the digestive tract, all blood slowly flows through the liver. In the liver cells, in addition to the formation of bile, foreign proteins and poisons that have entered with food are neutralized, glycogen is deposited, and in sharks and codfish (cod, burbot, etc.). - fat and vitamins. Having passed through the liver, the blood is directed through the hepatic vein to the heart.

The barrier function of the liver (purification of the blood from harmful substances) determines its most important role not only in digestion, but also in blood circulation.

The pancreas is a complex alveolar gland, also a derivative of the intestine, is a compact organ only in sharks and a few other fish. In most fish, it is not visually detected, since it is diffusely introduced into the liver tissue (for the most part), and therefore it can be distinguished only on histological preparations. Each lobule is associated with an artery, vein, nerve endings and duct that carries secretions to the gallbladder. Both glands are collectively called hepatopancreas.

The pancreas produces digestive enzymes that act on proteins, fats and carbohydrates (trypsin, erepsin, enterokokinase, lipase, amylase, maltase), which are excreted into the intestine.

In teleost fishes (for the first time among vertebrates), islets of Langerhans are found in the pancreatic parenchyma, in which there are numerous cells that synthesize insulin, which is released directly into the blood and regulates carbohydrate metabolism.

Thus, the pancreas is a gland of external and internal secretion.

From the sac-like invagination of the dorsal part of the beginning of the intestine, a swim bladder is formed in fish - an organ peculiar only to fish.

RESPIRATORY SYSTEM AND GAS EXCHANGE

The evolution of fish led to the emergence of the branchial apparatus, an increase in the respiratory surface of the gills, and the deviation from the main line of development led to the development of adaptations for using air oxygen. Most fish breathe oxygen dissolved in water, but there are species that have partially adapted to air respiration (lungs, jumper, snakeheads, etc.).

The main respiratory organs. The main organ for extracting oxygen from water is the gills.

The shape of the gills is varied and depends on the species and mobility: bags with folds (in fish-like), plates, petals, bundles of mucous membranes with a rich network of capillaries. All these devices are aimed at creating the largest surface with the smallest volume.

In teleost fishes, the branchial apparatus consists of five branchial arches located in the branchial cavity and covered by the branchial cover. The four arches on the outer convex side each have two rows of branchial lobes supported by supporting cartilages. Gill petals are covered with thin folds - petals. It is in them that gas exchange takes place. The number of petals varies; they account for 1 mm of the branchial lobe:

in pike - 15, flounder - 28, perch - 36. As a result, the useful respiratory surface of the gills is very large. The branchial artery approaches the base of the branchial lobes, its capillaries penetrate the petals; of these, oxidized (arterial) blood enters the aortic root through the outflowing branchial artery. In the capillaries, blood flows in the opposite direction to the flow of water

Fig. 1 Scheme of the counterflow of blood and water in the gills of fish:

1 - cartilaginous rod; 2 - branchial arch; 3 - gill petals; 4 - gill plates; 5 - bringing artery from the abdominal aorta; 6 - the outflowing artery to the dorsal aorta.

More active fish have a larger gill surface: in perch it is almost 2.5 times larger than in flounder. The backflow of blood in the capillaries and the water that washes the gills ensures complete saturation of the blood with oxygen. When inhaling, the mouth opens, the gill arches move to the sides, the gill covers are pressed tightly to the head by external pressure and close the gill slits. Due to the decrease in pressure, water is sucked into the gill cavity, washing the gill lobes. When you exhale, the mouth closes, the gill arches and gill covers come closer, the pressure in the gill cavity increases, the gill slits open and water is pushed out through them.

Rice. 2 Respiration mechanism of adult fish

When the fish swims, the flow of water can be created by moving with the mouth open. Thus, the gills are located, as it were, between two pumps - the oral (connected with the oral muscles) and the gill (associated with the movement of the operculum), the work of which creates the pumping of water and ventilation of the gills. During the day, at least 1 m 3 of water per 1 kg of body weight is pumped through the gills.

In the capillaries of the gill petals, oxygen is absorbed from the water (it is bound by blood hemoglobin) and carbon dioxide, ammonia, and urea are released.

The gills also play an important role in water-salt metabolism, regulating the absorption or excretion of water and salts. The branchial apparatus is sensitive to the composition of the water: toxicants such as ammonia, nitrites, CO2, with an increased content, affect the respiratory folds in the first 4 hours of contact.

Remarkable adaptations for respiration in fish during the embryonic period of development - in embryos and larvae, when the branchial apparatus is not yet formed, and the circulatory system is already functioning. At this time, the respiratory organs are:

a) the surface of the body and the system of blood vessels - Cuvier's ducts, veins of the dorsal and caudal fins, subintestinal vein, capillary network on the yolk sac, head, fin border and operculum; b) external gills

Rice. 3 Respiratory organs in fish embryos

a - pelagic fish; b - carp; c - loach; 1 - Cuvier's ducts; 2 - lower tail vein; 3 - a network of capillaries; 4 - external gills.

These are temporary, specific larval formations that disappear after the formation of definitive respiratory organs. The worse the conditions for respiration of embryos and larvae, the more the circulatory system or external gills develop. Therefore, in fish that are systematically close, but differing in the spawning ecology, the degree of development of the larval respiratory organs is different.

Additional respiratory organs. Additional devices that help to tolerate unfavorable oxygen conditions include aquatic skin respiration, that is, the use of oxygen dissolved in water with the help of the skin, and air respiration, the use of air using the swim bladder, intestines, or through special accessory organs

Breathing through the skin of the body is one of the characteristic features of aquatic animals. And although in fish the scales make it difficult to breathe with the surface of the body, in many species the role of the so-called skin respiration is great, especially in unfavorable conditions. According to the intensity of such respiration, freshwater fish are divided into three groups:

1. Fish that have adapted to live in conditions of severe oxygen deficiency. These are fish that inhabit well-warmed water bodies with a high content of organic matter, in which there is often a lack of oxygen. In these fish, the proportion of cutaneous respiration in the total respiration is 17 ... 22%, in some individuals - 42 ... 80%. These are carp, crucian carp, catfish, eel, loach. At the same time, fish, in which the skin is of the greatest importance in breathing, are devoid of scales or it is small and does not form a continuous cover. For example, in a loach, 63% of oxygen is absorbed by the skin, 37% by the gills; when the gills are turned off, up to 85% of the oxygen is consumed through the skin, and the rest enters through the intestines.

2. Fish experiencing less oxygen deficiency and less frequent exposure to adverse conditions. These include those living at the bottom, but in running water, sturgeon - sterlet, sturgeon, stellate sturgeon. The intensity of skin respiration in them is 9 ... 12%.

3. Fish that do not get into conditions of oxygen deficiency, living in flowing or non-flowing, but clean, oxygen-rich waters. The intensity of skin respiration does not exceed 3.3 ... 9%. These are whitefish, smelt, perch, ruff.

Carbon dioxide is also released through the skin. So, in loach this way up to 92% of the total is allocated.

Extraction of oxygen from the air in a humid atmosphere involves not only the surface of the body, but also the gills. Temperature is important here.

Crucian carp (11 days), tench (7 days), carp (2 days) are distinguished by the greatest survival in a humid environment, while bream, rudd, and bleak can live without water for only a few hours, and even then at low temperatures.

When live fish are transported without water, skin respiration almost entirely provides the body's need for oxygen.

Some fish living in unfavorable conditions have developed adaptations for breathing oxygen in the air. For example, breathing with the intestines. Clusters of capillaries form in the intestinal walls. The air swallowed through the mouth passes through the intestines, and in these places the blood absorbs oxygen and releases carbon dioxide, while up to 50% of the oxygen is absorbed from the air. This type of respiration is characteristic of loach, some catfish and carp fishes; its value is not the same for different fish. For example, in loaches under conditions of a high oxygen deficiency, this particular breathing method becomes almost equal to the branchial one.

When fish are killed, they swallow air by mouth; the air aerates the water in the mouth, which then passes through the gills.

Another way of using atmospheric air is the formation of special additional organs: for example, labyrinth in labyrinth fish, supra-gill in snakehead, etc.

Labyrinth fish have a labyrinth — an extended pocket-like section of the gill cavity, the folded walls of which are penetrated by a dense network of capillaries, in which gas exchange takes place. In this way, fish breathe oxygen from the atmosphere and can stay out of the water for several days (the tropical creeper Anabas sp. Comes out of the water and climbs rocks and trees).

In tropical mudskippers (Periophthalmus sp.), The gills are surrounded by a spongy tissue soaked in water. When these fish emerge on land, the gill covers are tightly closed and protect the gills from drying out. In the snakehead, the protrusion of the pharynx forms the supragillary cavity, the mucous membrane of its walls is equipped with a dense network of capillaries. Due to the presence of the supragillary organ, it breathes air and can be in shallow water at 30 ° C. For normal life, the snakehead, like the crawler, needs both oxygen dissolved in water and atmospheric oxygen. However, during wintering in ice-covered ponds, he does not use atmospheric air.

The swim bladder is also designed to use oxygen in the air. It reaches its greatest development as a respiratory organ in lung-breathing fish. They have it cellular and functions like a lung. In this case, there is a "pulmonary circle" of blood circulation,

The composition of gases in the swim bladder is determined both by their content in the reservoir and by the state of the fish.

Moving and predatory fish have a large supply of oxygen in the swim bladder, which is consumed by the body when throwing after prey, when the supply of oxygen through the respiratory organs is insufficient. In unfavorable oxygen conditions, the air of the swim bladder is used for breathing in many fish. The loach and eel can live outside the water for several days, provided that the moisture of the skin and gills is preserved: if in the water the gills provide 85 ... 90% of the total oxygen absorption to the eel, then only a third is in the air. Outside of water, the eel uses oxygen from the swim bladder and air through the skin and gills to breathe. This allows him to even crawl from one body of water to another. Carp and carp, which do not have any special devices for using atmospheric air, when they are out of water, partially absorb oxygen from the swim bladder.

While exploring various reservoirs, the fish have adapted to life under different gas regimes. The most demanding for the oxygen content in the water is salmonids, which need an oxygen concentration of 4.4 ... 7 mg / l for normal life; grayling, chub, burbot feel good with a content of at least 3.1 mg / l; carp is usually 1.9 ... 2.5 mg / l.

Each species has its own oxygen threshold, that is, the minimum oxygen concentration at which the fish perishes. Trout begins to suffocate at an oxygen concentration of 1.9 mg / l, pike perch and bream die at 1.2, roach and rudd at 0.25 ... 0.3 mg / l; in carp underyearlings reared on natural food, the oxygen threshold was noted at 0.07 ... 0.25 mg / l, and for two-year-olds - 0.01 ... 0.03 mg / l oxygen. Crucians and rotans - partial anaerobes - can live for several days completely without oxygen, but at low temperatures. It is believed that the body first uses oxygen from the swim bladder, then liver and muscle glycogen. Apparently, fish have special receptors in the anterior part of the dorsal aorta or in the medulla oblongata, which sense a drop in the oxygen concentration in the blood plasma. The endurance of fish is facilitated by a large amount of carotenoids in the nerve cells of the brain, which are able to accumulate oxygen and give it back in case of a lack.

Respiration rate depends on biotic and abiotic factors. Within one species, it changes depending on the size, age, mobility, nutritional activity, sex, degree of maturity of the gonads, physicochemical factors of the environment. As the fish grows, the activity of oxidative processes in the tissues decreases; maturation of the gonads, on the contrary, causes an increase in oxygen consumption. The oxygen consumption in the body of males is higher than that of females.

The breathing rhythm, in addition to the oxygen concentration in the water, is influenced by the content of CO2, pH, temperature, etc. For example, at a temperature of 10 ° C and an oxygen content of 4.7 mg / l, trout makes 60 ... 2 kg / l, the respiratory rate increases to 140 ... 160; carp at 10 ° C breathes almost twice as slow as trout (30 ... 40 times per minute), in winter it makes 3 ... 4 and even 1 ... 2 respiratory movements per minute.

As well as a sharp lack of oxygen, excessive oversaturation of water with it has a detrimental effect on fish. So, the lethal limit for pike embryos is 400% of water saturation with oxygen, at 350 ... 430% saturation the motor activity of roach embryos is disturbed. Sturgeon growth decreases at 430% saturation.

Incubation of eggs in oxygen-saturated water leads to a slowdown in the development of embryos, a strong increase in waste and the number of freaks, and even death. In fish, gas bubbles appear on the gills, under the skin, in the blood vessels, organs, and then convulsions and death occur. This is called gas embolism or gas bubble disease. However, death does not occur because of an excess of oxygen, but because of a large amount of nitrogen. For example, in salmonids, larvae and fry die at 103 ... 104%, underyearlings - 105 ... 113, adult fish - at 118% water saturation with nitrogen.

To maintain the optimal oxygen concentration in the water, which ensures the most efficient course of physiological processes in the fish organism, it is necessary to use aeration units.

Fish adapt quickly to a slight oversaturation of oxygen. Their metabolism increases and, as a result, feed consumption increases and the feed coefficient decreases, the development of embryos is accelerated, and waste is reduced.

For the normal respiration of fish, the content of CO2 in the water is very important. With a large amount of carbon dioxide, breathing of fish is difficult, since the ability of blood hemoglobin to bind oxygen decreases, blood oxygen saturation decreases sharply and the fish suffocates. When the CO2 content in the atmosphere is 1 ... 5% CO2; blood cannot flow outside, and blood cannot take oxygen even from oxygenated water.

Circulatory system

The main difference between the circulatory system of fish from other vertebrates is the presence of one circle of blood circulation and a two-chambered heart filled with venous blood (with the exception of dioecious and cross-finned).

The heart consists of one ventricle and one atrium and is placed in the pericardial sac, immediately behind the head, behind the last branchial arches, that is, in comparison with other vertebrates, it is shifted forward. In front of the atrium there is a venous sinus, or venous sinus, with falling walls; through this sinus, blood enters the atrium, and from it - into the ventricle.

The enlarged initial section of the abdominal aorta in lower fish (sharks, rays, sturgeon "lungs") forms a contracting arterial cone, and in higher fish - the aortic bulb, the walls of which cannot contract. Backflow of blood is impeded by valves.

The circulatory scheme in its most general form is presented as follows. The venous blood filling the heart, with the contractions of the strong muscular ventricle, through the arterial bulb along the abdominal aorta, is directed forward and rises into the gills along the supplying branchial arteries. In teleost fishes there are four of them on each side of the head, according to the number of branchial arches. In the branchial lobes, the blood passes through the capillaries and is oxidized, enriched with oxygen, directed through the outflow vessels (there are also four pairs of them) to the roots of the dorsal aorta, which then merge into the dorsal aorta, which runs back along the body, under the spine. The connection of the roots of the aorta in front forms the head circle, characteristic of teleost fishes. In front of the roots of the aorta, the carotid arteries branch off.

From the dorsal aorta, there are arteries to the internal organs and muscles. In the tail section, the aorta passes into the tail artery. In all organs and tissues, arteries disintegrate into capillaries. The venous capillaries collecting venous blood flow into a vein that carries blood to the heart. The tail vein, starting in the tail section, having entered the body cavity, is divided into the portal veins of the kidneys. In the kidneys, the branching of the portal veins form the portal system, and after leaving them, they merge into the paired posterior cardinal veins. As a result of the fusion of the posterior cardinal veins with the anterior cardinal (jugular), collecting blood from the head, and subclavian, bringing blood from the pectoral fins, two Cuvier ducts are formed, through which blood enters the venous sinus. Blood from the digestive tract (stomach, intestines) and spleen, going through several veins, is collected in the portal vein of the liver, the branches of which in the liver form the portal system. The hepatic vein that collects blood from the liver flows directly into the venous sinus

Rice. 1 Diagram of the circulatory system of teleost fish:

1 - venous sinus; 2 - atrium; 3 - ventricle; 4 - aortic bulb; 5 - abdominal aorta; 6 - bringing gill arteries; efferent branchial arteries; 8 - the roots of the dorsal aorta; 9 - anterior jumper connecting the roots of the aorta; 10 - carotid artery; 11 - dorsal aorta; 12 - subclavian artery; 13 - intestinal artery; 14 - mesenteric artery; 15 - tail artery; 16 - tail vein; 17 - portal veins of the kidneys; 18 - posterior cardinal vein; 19 - anterior cardinal vein; 20 - subclavian vein; 21 - Cuvier duct; 22 - portal vein of the liver; 23 - liver; 24 - hepatic vein; vessels with venous blood are shown in black, vessels with arterial blood are shown in white.

Like other vertebrates, cyclostomes and fish have so-called additional hearts that maintain pressure in the vessels. So, in the dorsal aorta of rainbow trout there is an elastic ligament, which acts as a pressure pump, which automatically increases blood circulation during swimming, especially in the muscles of the body. The intensity of the work of the additional heart depends on the frequency of movements of the caudal fin.

In lung-breathing fish, an incomplete atrial septum appears. This is accompanied by the appearance of the pulmonary circulation, passing through the swim bladder, turned into a lung.

The heart of fish is much smaller and weaker than the heart of terrestrial vertebrates. Its mass usually does not exceed 2.5%, on average 1% of body weight, while in mammals it reaches 4.6%, and in birds even 16%.

The blood pressure (Pa) in fish is low — 2133.1 (stingray), 11198.8 (pike), 15998.4 (salmon), while in the horse's carotid artery it is 20664.6.

The heart rate is also low — 18 ... 30 beats per minute, and it strongly depends on temperature: at low temperatures in fish wintering in pits, it decreases to 1 ... 2; in fish that endure freezing into ice, the heartbeat stops for this period.

The amount of blood in fish is less than in all other vertebrates (1.1, .. 7.3% of body weight, including carp 2.0 ... 4.7%, catfish - up to 5, pike - 2 , chum salmon - 1.6, while in mammals - 6.8% on average). This is due to the horizontal position of the body (there is no need to push the blood upward) and less energy expenditure due to life in the aquatic environment. Water is a hypogravitational medium, that is, the force of gravity is almost not affected here.

The morphological and biochemical characteristics of blood are different in different species due to the systematic position, the characteristics of the habitat and lifestyle. Within one species, these indicators fluctuate depending on the season of the year, conditions of detention, age, sex, condition of individuals. The erythrocytes of fish are larger, and their number in the blood is less than in higher vertebrates, while the leukocytes, as a rule, are larger. This is connected, on the one hand, with a reduced metabolism of fish, and on the other, with the need to strengthen the protective functions of the blood, since the environment is replete with pathogens. In 1 mm 3 of blood, the number of erythrocytes is (million): in primates - 9.27; ungulates — 11.36; cetaceans - 5.43; birds - 1.61 ... 3.02; teleost fish — 1.71 (freshwater), 2.26 (marine), 1.49 (anadromous).

The number of erythrocytes in fish varies widely, primarily depending on their mobility: in carp - 0.84 ... 1.89 million / mm 3 of blood, pike - 2.08, bonito - 4.12 million / mm 3. The number of leukocytes in carp is 20 ... 80, in ruff - 178 thousand / mm 3. Fish leukocytes are very diverse. In most species, the blood contains both granular (neutrophils, eosinophils) and non-granular (lymphocytes, monocytes) forms of leukocytes. Lymphocytes predominate, accounting for 80 ... 95%, monocytes make up 0.5 ... 11%, neutrophils - 13 ... 31%. Eosinophils are rare. For example, cyprinids, Amur herbivores and some perch fish have them.

The ratio of different forms of leukocytes in the blood of carp depends on the age and growing conditions.

The number of leukocytes varies greatly throughout the year:

in carp it increases in summer and decreases in winter during starvation due to a decrease in metabolic rate.

A variety of shapes, sizes and numbers is also characteristic of platelets involved in blood clotting.

The blood of fish is colored red with hemoglobin, but there are fish with colorless blood. In such fish, oxygen in a dissolved state is carried by the plasma. Thus, in representatives of the family Chaenichthyidae (from the suborder Nototheniaceae) living in the Antarctic seas at low temperatures (

The amount of hemoglobin in the body of fish is much less than in terrestrial vertebrates: they have 0.5 ... 4 g per 1 kg of body, while in mammals it is 5 ... 25 g. In fish that move quickly, there is more hemoglobin than in sedentary ones: in anadromous sturgeon 4 g / kg, in burbot 0.5 g / kg. The amount of hemoglobin depends on the season (in carp it increases in winter and decreases in summer), the hydrochemical regime of the reservoir (in water with a pH of 5.2, the amount of hemoglobin in the blood increases), nutritional conditions (carps grown on natural food and additional feed have different amounts of hemoglobin ). The growth rate of fish depends on the amount of hemoglobin.

Living in an environment with a low oxygen content has determined a low exchange rate and a higher saturation capacity at a lower partial pressure of oxygen, in contrast to vertebrates that breathe air. The ability of hemoglobin to extract oxygen from water varies from fish to fish. Fast swimming (mackerel, cod, trout) have a lot of hemoglobin in their blood, and they are very demanding on the oxygen content in the water. On the other hand, many bottom sea fish, as well as eels, carp, crucian carps and some others, have little hemoglobin in their blood, but it can take oxygen from the environment even with a small amount.

For example, to saturate the blood with oxygen (at 16 ° C), pike perch needs a water content of 2.1 ... 2.3 O2 mg / l; in the presence of 0.56 ... 0.6 O2 mg / l in the water, the blood begins to give it away, breathing becomes impossible, and the fish dies. For bream at the same temperature, for the complete saturation of hemoglobin with oxygen, the presence of 1.0 ... 1.06 mg of oxygen in a liter of water is sufficient.

The sensitivity of fish to changes in water temperature is also associated with the properties of hemoglobin: with an increase in temperature, the body's need for oxygen increases, but the ability of hemoglobin to take it away decreases.

Reduces the ability of hemoglobin to take oxygen and carbon dioxide: in order for the saturation of eel blood with oxygen to reach 50% with 1% CO2 in water, an oxygen pressure of 666.6 Pa is required, and in the absence of CO2, an oxygen pressure of almost half that is sufficient for this - 266, 6. „399.9 Pa,

Blood groups in fish were first determined on the Baikal omul and grayling in the 30s of this century. To date, it has been established that group antigenic differentiation of erythrocytes is widespread: 14 systems of blood groups have been identified, including more than 40 erythrocyte antigens. Using immunoserological methods, variability is studied at different levels: differences between species and subspecies and even between intraspecific groups in salmon (when studying the relationship of trout), sturgeon (when comparing local stocks) and other fish have been revealed.

Blood, being the internal environment of the body, performs the most important functions: it transports proteins, carbohydrates (glycogen, glucose, etc.) and other nutrients that play an important role in energy and plastic metabolism; respiratory — transporting oxygen to the tissues and carbon dioxide to the respiratory organs; excretory — removal of end products of metabolism to the excretory organs; regulatory — the transfer of hormones and other active substances from the endocrine glands to organs and tissues; protective - the blood contains antimicrobial substances (lysozyme, complement, interferon, properdin), antibodies are formed, leukocytes circulating in it have phagocytic ability. The level of these substances in the blood depends on the biological characteristics of fish and abiotic factors, and the mobility of the blood composition makes it possible to use its indicators to assess the physiological state.

Bone marrow, which is the main organ for the formation of blood corpuscles in higher vertebrates, and lymph glands (nodes) in fish are absent.

Compared to higher vertebrates, hematopoiesis in fish differs in a number of features.

1. The formation of blood cells occurs in many organs. The foci of hematopoiesis are: the branchial apparatus (vascular endothelium and reticular syncytium, concentrated at the base of the branchial lobes), intestine (mucous membrane), heart (epithelial layer and vascular endothelium), kidneys (reticular syncytium between the tubules), spleen, vascular blood, lymphoid organ ( accumulations of hematopoietic tissue - reticular syncytium - under the roof of the skull). Blood cells of different stages of development are visible on the prints of these organs.

2. In teleost fish, hematopoiesis most actively occurs in the lymphoid organs, kidney and spleen, and the main organ of hematopoiesis is the kidneys, namely their anterior part. In the kidneys and spleen, both the formation of erythrocytes, leukocytes, platelets, and the breakdown of erythrocytes occur.

3. The presence of mature and young erythrocytes in the peripheral blood of fish is normal and does not serve as a pathological indicator, in contrast to the blood of adult mammals.

4. Erythrocytes have a nucleus, like other aquatic animals, as a result of which their viability is longer than that of mammals.

The spleen of fish is located in front of the body cavity, between the intestinal loops, but independently of it. This is a dense compact dark red formation of various shapes (spherical, ribbon-like), but more often elongated.

The spleen rapidly changes volume under the influence of external conditions and the condition of the fish. In carp, it increases in winter, when, due to a reduced metabolism, the blood flow slows down and it accumulates in the spleen, liver and kidneys, which serve as a blood depot, the same is observed in acute diseases. With a lack of oxygen, water pollution, transportation and sorting of fish, fishing in ponds, supplies from the spleen enter the bloodstream.

One of the most important factors of the internal environment is the osmotic pressure of the blood, since the interaction of blood and body cells, water exchange in the body depends on it.

The circulatory system obeys the nervous (vagus nerve) and humoral (hormones, Ca, K ions) regulation. The central nervous system of fish receives information about the work of the heart from the baroreceptors of the branchial vessels.

The lymphatic system of fish has no glands. It is represented by a number of paired and unpaired lymphatic trunks, into which lymph is collected from the organs and through them is also excreted into the final sections of the veins, in particular into the Cuvierian ducts. Some fish have lymphatic hearts.

NERVOUS SYSTEM AND SENSORS

Nervous system. In fish, it is represented by the central nervous system and the peripheral and autonomic (sympathetic) nervous system associated with it.
The central nervous system consists of the brain and spinal cord. The peripheral nervous system includes nerves that extend from the brain and spinal cord to the organs. The autonomic nervous system is based on numerous ganglia and nerves that innervate the muscles of the internal organs and blood vessels of the heart.
The nervous system of fish, in comparison with the nervous system of higher vertebrates, is characterized by a number of primitive features.
The central nervous system looks like a neural tube stretching along the body: a part of it lying above the spine and protected by the upper arches of the vertebrae forms the spinal cord, and the expanded front part, surrounded by a cartilaginous or bony skull, makes up the brain.

Rice. 1 Fish brain (perch):

1- olfactory capsules; 2- olfactory lobes; 3- forebrain; 4- midbrain; 5- cerebellum; 6- medulla oblongata; 7- spinal cord; 8,9,10- head nerves.

The cavities of the anterior, diencephalon and medulla oblongata are called the ventricles: the cavity of the midbrain is called the sylvian aqueduct (it connects the cavities of the diencephalon and medulla oblongata, i.e., the third and fourth ventricles).
The forebrain, due to the longitudinal groove, has the appearance of two hemispheres. Olfactory bulbs (primary olfactory center) adjoin them either directly (in most species), or through the olfactory tract (carp, catfish, cod).
There are no nerve cells in the roof of the forebrain. Gray matter in the form of striated bodies is concentrated mainly in the base and olfactory lobes, lines the cavity of the ventricles and makes up the main mass of the forebrain. The fibers of the olfactory nerve connect the bulb with. cells of the olfactory capsule.
The forebrain is the center for processing information from the olfactory organs. Due to its connection with the diencephalon and midbrain, it is involved in the regulation of movement and behavior. In particular, the forebrain takes part in the formation of the ability for such acts as spawning, guarding eggs, the formation of a flock, aggression, etc.
In the diencephalon, the visual hillocks are developed. The optic nerves depart from them, forming a chiasm (cross, that is, part of the fibers of the right nerve passes into the left nerve and vice versa). On the underside of the diencephalon, or hypothalamus, there is a funnel, to which the pituitary gland, or pituitary gland, is adjacent; in the upper part of the diencephalon, the pineal gland, or pineal gland, develops. The pituitary and pineal glands are endocrine glands.
The diencephalon has numerous functions. He perceives irritations from the retina of the eye, participates / in the coordination of movements, the processing of information from other senses. The pituitary gland and pineal gland carry out hormonal regulation of metabolic processes.
The midbrain is the largest in volume. It looks like two hemispheres, which are called the visual lobes. These lobes are the primary visual arousal centers. The fibers of the optic nerve originate from them.
The midbrain processes signals from the organs of vision and balance; here are the centers of communication with the cerebellum, medulla oblongata and spinal cord, regulation of color, taste.
The cerebellum is located in the back of the brain and can have the form of either a small tubercle adjacent to the back of the midbrain, or a large saccular-elongated formation adjacent to the medulla oblongata from above. The cerebellum is especially developed in catfish, and in the mormyrus it is the largest among all vertebrates. The cerebellum of fish contains Purkinje cells.
The cerebellum is the center of all motor innervations for swimming and grasping food. It "provides coordination of movements, maintenance of balance, muscle activity, is associated with receptors of the lateral line organs, directs and coordinates the activity of other parts of the brain. When the cerebellum is damaged, for example, in carp and goldfish, muscle atony occurs, balance is disturbed, is not produced or disappears conditioned reflexes to light and sound.
The fifth section of the brain, the medulla oblongata, passes into the spinal cord without a sharp border. Medulla oblongata - the fourth ventricle continues into the cavity
the spinal cord is a neurocoel. A significant mass of the medulla oblongata consists of white matter.
Most (six out of ten) of the cranial nerves depart from the medulla oblongata. It is the center for the regulation of the spinal cord and the autonomic nervous system. It contains the most important vital centers that regulate the activities of the respiratory, musculoskeletal, circulatory, digestive, excretory systems, organs of hearing and balance, taste, lateral line and electrical organs. Therefore, when the medulla oblongata is destroyed, for example, when the body is cut behind the head, the fish die quickly.
Through the spinal fibers entering the medulla oblongata, the connection between the medulla oblongata and the spinal cord is carried out.
10 pairs of cranial nerves depart from the brain: 1 — the olfactory nerve (nervus olfactorius) from the sensory epithelium of the olfactory capsule brings irritations to the olfactory bulbs of the forebrain; 2 — the optic nerve (n. Opticus) extends to the retina from the optic tubercles of the diencephalon; 3 - the oculomotor nerve (n. Oculo-motorius) innervates the muscles of the eye, departing from the midbrain;
4 - trochlear nerve (n. Trochlearis) - oculomotor, stretching from the midbrain to one of the muscles of the eye; 5 — trigeminal nerve (n. Trigeminus), extending from the lateral surface of the medulla oblongata and giving three main branches — orbital, maxillary and mandibular; 6 - the abducent nerve (n. Abducens) stretches from the bottom of the brain to the rectus muscle of the eye; 7 — the facial nerve (n. Facialis) departs from the medulla oblongata and gives numerous branches to the muscles of the hyoid arch, oral mucosa, scalp (including the lateral line of the head); 8 - the auditory nerve (n. Acusticus) connects the medulla oblongata and the hearing aid; 9 - lingo-pharyngeal nerve (n. Glossopharingeus) goes from the medulla oblongata to the pharynx, innervates the pharyngeal mucosa and the muscles of the first branchial arch; 10 - vagus nerve (n. Vagus) - the longest, connects the medulla oblongata with the branchial apparatus, intestinal tract, heart, swim bladder, lateral line.
The degree of development of different parts of the brain is different in different groups of fish and is associated with the way of life.
The forebrain and olfactory lobes are better developed in cartilaginous fish (sharks and rays) and worse in teleosts. In sedentary fish, for example, bottom fish (flounder), the cerebellum is small, but the anterior and oblong brain regions are more developed in accordance with the large role of smell and touch in their life. In well-swimming fish (pelagic, plankton-feeding and predatory), the midbrain (visual lobes) and cerebellum (due to the need for rapid coordination of movement) are more developed. Fish that live in muddy waters have small visual lobes and a small cerebellum. The visual lobes are poorly developed in deep-sea fish. The electrical activity of different parts of the brain is also different: in the goldfish, electrical waves in the cerebellum go with a frequency of 25 ... 35 times per second, in the forebrain - 4 ... 8.
The spinal cord is an extension of the medulla oblongata. It has the shape of a rounded cord and lies in the canal formed by the superior arches of the vertebrae. Unlike higher vertebrates, it is capable of regeneration and restoration of activity. In the spinal cord, the gray matter is located inside and the white matter is outside.
The spinal cord function is reflexive and conductive. It contains the centers of vasomotor, trunk muscles, chromatophores, electrical organs. From the spinal cord metamerically, that is, according to each vertebra, the spinal nerves that innervate the surface of the body, the trunk muscles, and due to the connection of the spinal nerves with the ganglia of the sympathetic nervous system, also the internal organs. In the spinal cord of teleost fish there is a secretory organ - the urohypophysis, the cells of which produce a hormone involved in water metabolism.
The autonomic nervous system in cartilaginous fish is represented by disconnected ganglia lying along the spine. The cells of the ganglia with their processes are in contact with the spinal nerves and internal organs.
In teleost fish, the ganglia of the autonomic nervous system are connected by two longitudinal nerve trunks. The connecting branches of the ganglia connect the autonomic nervous system with the central one. The interrelationships of the central and autonomic nervous systems create the possibility of some interchangeability of the nerve centers.
The autonomic nervous system acts independently of the central nervous system and determines the involuntary automatic activity of internal organs, even if its connection with the central nervous system is broken.
The reaction of the fish organism to external and internal stimuli is determined by the reflex. In fish, you can develop a conditioned reflex to light, shape, smell, taste, sound, water temperature and salinity. So, aquarium and pond fish, soon after the start of regular feeding, accumulate at a certain time at the feeders. They also get used to sounds during feeding (tapping on the walls of the aquarium, ringing a bell, whistling, banging) and for some time swim up to these stimuli even in the absence of food. At the same time, reflexes to receive food are formed in fish faster, and disappear more slowly than in chickens, rabbits, dogs, and monkeys. In crucian carp, the reflex appears after 8 combinations of a conditioned stimulus with an unconditioned one, and fades out after 28 ... 78 unsupported signals.
Behavioral reactions are developed in fish faster in the Group (imitation, movement after the leader in the flock, reaction to a predator, etc.). Temporary memory and training is also of great importance in fish farming practice. If fish are not taught defensive reactions, the skills of communicating with predators, then juveniles released from fish hatcheries quickly die in natural conditions.
The organs of perception of the environment (sense organs) of fish have a number of features that reflect their adaptability to living conditions. The ability of fish to perceive information from the environment is manifold. Their receptors can pick up various irritations of both physical and chemical nature: pressure, sound, color, temperature, electric and magnetic fields, smell, taste. Some irritations are perceived as a result of direct touch (touch, taste), others at a distance.
Organs that perceive chemical, tactile (touch), electromagnetic, temperature and other stimuli have a simple structure. Irritations are trapped by the free nerve endings of the sensory nerves on the surface of the skin. In some groups of fish, they are represented by special organs or are part of the lateral line.
In connection with the peculiarities of the living environment in fish, chemical sense systems are of great importance. Chemical irritations are perceived with the help of the sense of smell (the sense of smell) or the organs of non-smelling reception, which provide the perception of taste, a change in the activity of the environment, etc.
The chemical sense is called chemoreception, and the sensory organs are called chemoreceptors. Chemoreception helps fish find and evaluate food, individuals of their own species and of the opposite sex, avoid enemies, navigate the stream, and defend territory.
The organs of smell. In fish, like other vertebrates, they are located in the front part of the head and are represented by paired olfactory (nasal) sacs (capsules) that open outward with openings — nostrils. The bottom of the nasal capsule is lined with folds of the epithelium, which consists of supporting and sensory cells (receptors). The outer surface of the sensory cell is provided with cilia, and the base is connected to the endings of the olfactory nerve. Receptor surface
organ is large: in the 1st quarter. mm. the olfactory epithelium has 95,000 receptor cells in Phoxinus. The olfactory epithelium contains numerous mucus-secreting cells.
The nostrils are located in cartilaginous fishes on the underside of the snout in front of the mouth, in bony fishes - on the dorsal side between the mouth and the eyes. Roundstomes have one nostril, true fish have two. Each nostril is divided by a leathery septum into two parts called openings. Water enters the anterior, washes the cavity and exits through the posterior opening, washing and irritating the hairs of the receptors.
Under the influence of odorous substances in the olfactory epithelium, complex processes occur: the movement of lipids, protein-mucopolysaccharide complexes and acid phosphatase. The electrical activity of the olfactory epithelium in response to different odorous substances is different.
The size of the nostrils is related to the way of life of the fish: in mobile fish they are small, since during fast swimming the water in the olfactory cavity is renewed quickly; in sedentary fish, the nostrils are large, they pass a larger volume of water through the nasal cavity, which is especially important for poor swimmers, in particular, those living at the bottom.
Fish have a fine sense of smell, that is, their olfactory sensitivity thresholds are very low. This especially applies to nocturnal and crepuscular fish, as well as to those living in muddy waters, for which sight helps little in finding food and communicating with relatives.
The sense of smell is most sensitive in anadromous fish. Far Eastern salmon definitely find their way from the feeding grounds in the sea to the spawning grounds in the upper reaches of the rivers, where they hatched several years ago. At the same time, they overcome huge distances and obstacles — currents, rapids, rifts. However, fish find their way correctly only if the nostrils are open, and if they are filled with cotton wool or petroleum jelly, then the fish go randomly. It is assumed that at the beginning of their migration salmon are guided by the sun and the stars and, approximately 800 km from their native river, unmistakably determine the path due to chemoreception.
In experiments, when the nasal cavity of these fish was washed off with water from their native spawning ground, a strong electrical reaction arose in the olfactory bulb of the brain. The reaction to water from downstream tributaries was weak, and receptors did not react at all to water from foreign spawning grounds.
Young salmon can distinguish, with the help of olfactory bulb cells, the water of different lakes, solutions of various amino acids in a dilution of 10 "4, as well as the concentration of calcium in water.
eel migrating from Europe to spawning grounds in the Sargasso Sea. It is estimated that eel is able to recognize the concentration created by diluting 1 g of phenylethyl alcohol in a ratio of 1: 3-10-18. Fish capture the fear pheromone at a concentration of 10 -10 g / l: High selective sensitivity to histamine and carbon dioxide (0.00132 ... 0.0264 g / l) was found in carp.
The olfactory receptor of fish, in addition to chemical ones, is capable of perceiving mechanical influences (stream streams) and temperature changes.
The organs of taste. They are represented by taste buds, formed by accumulations of sensory and supporting cells. The bases of the sensory cells are braided by the terminal ramifications of the facial, vagus and glossopharyngeal nerves. The perception of chemical stimuli is also carried out by the free nerve endings of the trigeminal, vagus and spinal nerves.
The perception of taste by fish is not necessarily associated with the oral cavity, since taste buds are located in the mucous membrane of the oral cavity, on the lips, in the pharynx, on the antennae, gill lobes, fin rays, and throughout the body surface, including the tail.
Catfish perceives taste mainly with the help of whiskers, since taste buds are concentrated in their epidermis. The number of these buds increases as the fish's body size increases.
Fish also distinguish the taste of food: bitter, salty, sour, sweet. In particular, the perception of salinity is associated with a pit-shaped organ located in the oral cavity.
The sensitivity of the taste organs in some fish is very high: for example, the cave fish Anoptichtys, being blind, sense a glucose solution at a concentration of 0.005%. Fish recognize changes in salinity up to O.3 ^ / oo, pH — 0.05 ... 0.007, carbon dioxide — 0.5 g / l, NaCl — 0.001 ... 0.005 mole (cyprinids), and minnow even 0.00004 praying.
The lateral line sense organs. A specific organ peculiar only to fish and amphibians living in water is the lateral sense organ, or lateral line. It is a seismosensory specialized skin organ. These organs are most simply arranged in cyclostomes and cyprinid larvae. Sensory cells (mechanoreceptors) lie among the accumulations of ectodermal cells on the surface of the skin or in small pits, At the base, they are braided by the terminal branches of the vagus nerve, and in the area that rises above the surface, they have cilia that perceive water vibrations. In most adult bony bones, these organs are
channels immersed in the skin, stretching along the sides of the body along the midline. The channel opens outward through holes (pores) in the scales located above it. Branches of the lateral line are also present on the head.

At the bottom of the canal, there are groups of sensory cells with cilia. Each such group of receptor cells, together with the nerve fibers in contact with them, forms an organ proper — a neuromast. Water flows freely through the channel and the cilia feel its pressure. In this case, nerve impulses of different frequencies arise.
The lateral line organs are connected to the central nervous system by the vagus nerve.
The lateral line can be complete, that is, extend along the entire length of the body, or incomplete and even absent, but in the latter case, the head canals are strongly developed, as, for example, in herring.
With the lateral line, the fish senses changes in the pressure of the flowing water, vibrations (vibrations) of low frequency, infrasonic vibrations and electromagnetic fields. For example, carp catches current at a density of 60 µA / cm 2, crucian carp — 16 µA / cm 2.
The lateral line captures the pressure of the moving stream, and it does not perceive the change in pressure when diving to depth. Catching fluctuations in the water column, the fish detects surface waves, currents, underwater stationary (rocks, reefs) and moving (enemies, prey) objects.
The lateral line is a very sensitive organ: the shark catches the movement of fish at a distance of 300 m, anadromous fish feel even slight currents of fresh water in the sea.
The ability to catch waves reflected from living and inanimate objects is very important for deep-sea fish, since normal visual perception is impossible in the dark at great depths.
It is assumed that during mating games, fish perceive by the lateral line of the wave as a signal of the female or male to spawn. The function of the skin feeling is also performed by the so-called skin kidneys - cells found in the integument of the head and antennae, to which the nerve endings fit, but they are of much lesser importance.
Tactile organs. They are clusters of sensory cells (tactile bodies) scattered over the surface of the body. They sense the touch of solid objects (tactile sensations), water pressure, temperature changes, and pain.
Especially many sensory skin buds are found in the mouth and on the lips. In some fish, the function of these organs is performed by elongated rays of the fins: in gourami, this is the first ray of the pelvic fin; in trigly (sea cock), the sense of touch is associated with the rays of the pectoral fins, feeling the bottom. In the inhabitants of muddy waters or bottom fish, which are most active at night, the largest number of sensory buds is concentrated on antennae and fins. In males, the whiskers serve as taste receptors.
Fish seem to feel less mechanical trauma and pain than other vertebrates. So, sharks, pounced on prey, do not react to blows with a sharp object in the head.
Thermoreceptors. They are the free endings of the sensory nerves located in the surface layers of the skin, with the help of which fish perceive the temperature of the water. There are receptors that perceive heat (heat) and cold (cold). Points of perception of heat have been found, for example, on a pike on the head, perception of cold - on the surface of the body. Bony fish catch temperature drops of 0.1 ... 0.4 degrees. In trout, you can develop a conditioned reflex to very small (less than 0.1 degrees) and rapid temperature changes.
The lateral line and the brain are very sensitive to temperature. In the brain of fish, temperature-sensitive neurons are found, similar to neurons in the thermoregulatory centers of mammals. Trout has neurons in the diencephalon that respond to temperature rise and fall.
Organs of electrical sense. The organs of perception of electric and magnetic fields are located in the skin on the entire surface of the fish's body, but mainly in different parts of the head and around it. They are similar to the lateral line organs:
these are pits filled with a mucous mass that conducts current well; at the bottom of the pits, sensory cells (electroreceptors) are placed, transmitting "nerve impulses to the brain. Sometimes they are part of the lateral line system. Lorenzini ampullae also serve as electrical receptors in cartilaginous fish. Analysis of the information received by electroreceptors is carried out by the lateral line analyzer, which is located in The sensitivity of fish to the current is high - up to 1 μV / cm2: carp senses a current with a voltage of 0.06 ... 0.1, trout - 0.02 ... 0.08, crucian carp 0.008 ... 0, 0015 V. It is assumed that the perception of changes in the Earth's electromagnetic field allows
It allows fishes to detect the approach of an earthquake 6 ... 24 hours before the start within a radius of up to 2 thousand km.
Organs of vision. They are basically the same as in other vertebrates. The mechanism of perception of visual sensations is similar to the rest of the vertebrates: light enters the eye through the transparent cornea, then the pupil (hole in the iris) passes it to the lens, and the lens transmits (focuses) light to the inner wall of the eye (retina), where and there is a direct perception of it (Fig. 3). The retina consists of light-sensitive (photoreceptor), nerve and supporting cells.

Light-sensitive cells are located on the side of the pigment membrane. In their processes, which are shaped like rods and cones, there is a light-sensitive pigment. The number of these photoreceptor cells is very large: for 1 mm 2 of the retina, there are 50 thousand of them in carp, 162 thousand in squid, 16 in spider, and 400 thousand in humans. Through a complex system of contacts between the terminal branching of sensory cells and dendrites of nerve cells, light stimuli enter the optic nerve.
Cones in bright light perceive the details of objects and color: they capture long wavelengths of the spectrum. The rods perceive weak light, but they cannot create a detailed image: perceiving short waves, they are about 1000 times more sensitive than cones.
The position and interaction of pigment membrane cells, rods and cones changes depending on the light. In the light, pigment cells expand and cover the rods around them; the cones are pulled up to the nuclei of the cells and thus move towards the light. In the dark, sticks are pulled up to the nuclei and are closer to the surface; the cones approach the pigment layer, and the pigment cells that have contracted in the dark cover them.
The number of receptors of various kinds depends on the lifestyle of the fish. In daytime fish, cones prevail in the retina, in crepuscular and nocturnal fishes - rods: in burbot rods are 14 times more than in pike. In deep-sea fish living in the dark of the depths, there are no cones, but the rods become larger and their number sharply increases — up to 25 million per 1 mm 2 of the retina; the likelihood of capturing even weak light increases. Most fish are color-sensitive. Some features in the structure of fish eyes are associated with the peculiarities of life in the water. They are elliptical in shape and have a silvery shell between the vascular and protein shell, rich in guanine crystals, which gives the eye a greenish-golden sheen. Cornea
fish is almost flat (not convex), the lens is spherical (not biconvex) —this expands the field of vision. The hole in the iris (pupil) can only change its diameter to a small extent. As a rule, fish have no eyelids. Only sharks have a nictitating membrane that covers the eye like a curtain, and some herring and mullet have a fatty eyelid — a transparent film that covers part of the eye.
The location of the eyes in most species on the sides of the head is the reason that fish have mainly monocular vision, and the ability to binocular vision is limited. The spherical shape of the lens and its forward movement towards the cornea provides a wide field of vision: light enters the eye from all sides. The vertical angle of view is 150 °, the horizontal angle is 168 ... 170 °. But at the same time, the spherical shape of the lens determines the myopia of fish. Their range of vision is limited and fluctuates due to the turbidity of the water from several centimeters to several tens of meters. Long-distance vision is made possible by the fact that the lens can be pulled back by a special muscle, the crescent-shaped process, coming from the choroid of the fundus of the optic cup, and not by changing the curvature of the lens, as in mammals.
With the help of sight, fish are also oriented relative to objects on the ground.
Improvement of vision in the dark is achieved by the presence of a reflective layer (tapetum) - guanine crystals, underlain by pigment. This layer t transmits light to the tissues behind the retina, and reflects it and returns it again.
on the retina. This increases the ability of the receptors to use the light that enters the eye.
Due to the living conditions, the eyes of fish can be greatly modified. In cave or abyssal (deep-sea) forms, the eyes can be reduced and even disappear. Some deep-sea fish, on the contrary, have huge eyes that allow them to catch very weak light, or telescopic eyes, the collecting lenses of which the fish can put in parallel and gain binocular vision. The eyes of some eels and tropical fish larvae are carried forward on long outgrowths (stalked eyes). An unusual modification of the eyes in the four-eyed, living in the waters of Central and South America. Her eyes are placed on the top of the head, each of them is divided by a partition into two independent parts:
the top fish sees in the air, the bottom - in the water. In the air, the eyes of fish crawling out onto land can function.
In addition to the eyes, the pineal gland (endocrine gland) and light-sensitive cells located in the tail, for example, in lampreys, perceive light.
The role of vision as a source of information for most fish is great: when orienting while moving, looking for food, preserving the school, during the spawning period (the perception of defensive and aggressive postures and movements by rival males, and between individuals of different sexes "- breeding plumage and spawning "Ceremonial"), in the relationship prey-predator, etc. Carp sees at an illumination of 0.0001 lux, crucian carp - 0.01 lux.
The ability of fish to perceive light has long been used in fishing: fishing for light.
It is known that fish of different species react differently to light of different intensities and different wavelengths, i.e., different colors. Thus, bright artificial light attracts some fish (Caspian sprat, saury, horse mackerel, mackerel) and scares away others (mullet, lamprey, eel). Also, different types are selectively related to different colors and different light sources - above-water and underwater. All this is the basis for the organization of industrial fishing with electric light. This is how they catch sprat, saury and other fish.
The organ of hearing and balance of fish. It is located at the back of the skull and is represented by a labyrinth. There are no ear openings, auricle and cochlea, that is, the organ of hearing is represented by the inner ear.
It reaches the greatest difficulty in real fish:
a large membranous labyrinth is placed in the cartilaginous or bony chamber under the cover of the ear bones. It distinguishes between the upper part - an oval sac (ear, utriculus) and the lower - a round sac (sacculus). From the top. parts in mutually perpendicular directions depart three semicircular canals, each of which at one end is expanded into an ampoule

An oval sac with semicircular canals constitutes the organ of balance (vestibular apparatus). Lateral expansion of the lower part of the round sac (lagena), which is the rudiment of the snail, does not receive further development in fish. An internal lymphatic (endolymphatic) canal departs from the round sac, which in sharks and rays goes out through a special opening in the skull, and in other fish it blindly ends at the scalp.
The epithelium lining the parts of the labyrinth has sensory cells with hairs extending into the internal cavity. Their bases are braided with branches of the auditory nerve.
The cavity of the labyrinth is filled with endolymph; it contains "auditory" stones, consisting of carbonic lime (otoliths), three on each side of the head: in oval and round sacs and lagen. Concentric layers are formed on otoliths, as well as on scales, therefore otoliths, especially the largest, are often used to determine the age of fish, and sometimes for systematic determinations, since their sizes and contours are not the same in different species.
In most fish, the largest otolith is located in a round sac, but in cyprinids and some others, in lagen.
A sense of balance is associated with the labyrinth: when the fish moves, the pressure of the endolymph in the semicircular canals, as well as from the side of the otolith, changes, and the resulting irritation is captured by the nerve endings. With the experimental destruction of the upper part of the labyrinth with semicircular canals, the fish loses the ability to maintain balance and lies on its side, back, or belly. The destruction of the lower part of the labyrinth does not lead to loss of balance.
The perception of sounds is associated with the lower part of the labyrinth: when the lower part of the labyrinth with a round sac and lagged fish is removed, they cannot distinguish sound tones, for example, during the development of conditioned reflexes. Fish without an oval sac and semicircular canals, that is, without the upper part of the labyrinth, lend themselves to training. Thus, it has been established that it is the round sac and lagena that act as sound receptors.
Fish perceive both mechanical and sound vibrations with a frequency of 5 to 25 Hz by the lateral line organs, from 16 to 13000 Hz: - a labyrinth. Some fish species pick up vibrations located on the border of infrasonic waves, lateral line, labyrinth and skin receptors.
The hearing acuity in fish is less than in higher vertebrates, and is not the same for different species: the ide perceives vibrations, the wavelength of which is 25 ... 5524 Hz, the goldfish — 25 ... 3840, the eel — 36 ... 650 Hz , moreover, low sounds are picked up by them better. Sharks hear sounds made by fish at a distance of 500 m.
Fish also pick up those sounds, the source of which is not in the water, but in the atmosphere, despite the fact that such a sound is 99.9% reflected by the surface of the water and, therefore, only 0.1% of the generated sound waves penetrate into the water.
In the perception of sound in cyprinids and catfish, the swim bladder, connected to the labyrinth and serving as a resonator, plays an important role.
Fish can make sounds themselves. The sound-producing organs in fish are different. These are the swim bladder (humps, wrasses, etc.), the rays of the pectoral fins in combination with the bones of the shoulder girdle (catfish), jaw and pharyngeal teeth (perch and cyprinids), etc. In this regard, the nature of sounds is also different. They can resemble blows, clatter, whistle, grunt, grunt, squeak, croak, growl, crackle, rumble, ringing, wheezing, honking, birdcrying and insect chirping.
The strength and frequency of sounds emitted by fish of the same species depends on gender, age, food activity, health, pain caused, etc.
The sound and perception of sounds is of great importance in the life of fish. It helps individuals of different sexes to find each other, preserve the flock, inform relatives about the presence of food, protect the territory, nest and offspring from enemies, is a stimulant of maturation during mating games, that is, it serves as an important means of communication. It is assumed that in deep-sea fish dispersed in the dark at ocean depths, it is hearing in combination with the lateral line organs and sense of smell that provides communication, especially since the sound conductivity, which is higher in water than in air, increases at depth. Hearing is especially important for nocturnal fish and inhabitants of murky waters.
The reaction of different fish to extraneous sounds is different: with noise, some go to the side, others (silver carp, salmon, mullet) jump out of the water. This is used when organizing fishing. In fish farms, during the spawning period, traffic around the spawning ponds is prohibited.

Endocrine glands

The endocrine glands are the pituitary gland, pineal gland, adrenal glands, pancreas, thyroid and ultimobronchial (esophageal) glands, as well as the urohypophysis and gonads.They secrete hormones into the blood.
The pituitary gland is an unpaired, irregular oval-shaped formation extending from the lower side of the diencephalon (hypothalamus). Its shape, size and position are extremely varied. In carp, carp and many other fish, the pituitary gland is heart-shaped, lying almost perpendicular to the brain. In goldfish it is elongated, slightly flattened from the sides and lies parallel to the brain.
In the pituitary gland, two main divisions of different origins are distinguished: the cerebral (neurohypophysis), which forms the inner part of the gland, which develops from the lower wall of the diencephalon as an invagination of the bottom of the third cerebral ventricle, and the glandular (adenohypophysis), formed from the invagination of the upper pharyngeal wall. In the adenohypophysis, three parts are distinguished (lobes, lobes): the main (anterior, located on the periphery), transitional (largest) and intermediate (Fig. 34). The adenohypophysis is the central gland of the endocrine system. In the glandular parenchyma of its lobes, a secret is produced that contains a number of hormones that stimulate growth (somatic hormone is necessary for bone growth), regulate the functions of the gonads and thus affect puberty, affecting the activity of pigment cells (determine the color of the body and, above all, the appearance of the nuptial dress ) and increase the resistance of fish to high temperatures, stimulates protein synthesis, thyroid function, and participates in osmoregulation. Removal of the pituitary gland entails an arrest of growth and maturation.
Hormones secreted by the neurohypophysis are synthesized in the nuclei of the hypothalamus and are transported along nerve fibers to the neurohypophysis, and then enter the capillaries that penetrate it.Thus, this is a neutrosecretory gland. Hormones take part in osmoregulation and cause spawning reactions.
A single system with the pituitary gland is formed by the hypothalamus, whose cells secrete a secret that regulates the hormone-forming activity of the pituitary gland, as well as water-salt metabolism, etc.
The most intensive development of the pituitary gland occurs during the period of transformation of the larva into fry. In sexually mature fish, its activity is uneven due to the biology of fish reproduction and, in particular, to the nature of spawning. In spawning fish, a secret in glandular cells accumulates almost simultaneously "after the secretion is excreted, by the time of ovulation the pituitary gland is emptied, and there is a break in its secretory activity. By the time of spawning, the development of oocytes ends in the ovaries, which are prepared for spawning in a given season. Ovocytes are swept out in one reception and thus constitute the only generation,
In portion-spawning fish, the secretion in the cells is not formed simultaneously. As a result, after the secretion is removed during the first spawning, some cells remain in which the colloid formation process has not ended. As a result, it can be released in portions throughout the entire spawning period. In turn, the oocytes, which are prepared for brooding in a given season, also develop asynchronously. By the time of the first spawning, the ovaries contain not only matured oocytes, but also those whose development has not yet been completed. Such oocytes mature some time after the first generation of oocytes is removed, that is, the first portion of eggs. This creates several servings of caviar.
The study of ways to stimulate the maturation of fish led almost simultaneously in the first half of this century, but independently of each other, Brazilian (Iering and Cardozo, 1934-1935) and Soviet scientists (Gerbilsky and his school, 1932-1934) to develop a method of pituitary injections into producers to accelerate their maturation. This method made it possible to largely control the process of maturation of fish and thereby increase the scope of fish breeding works for the reproduction of valuable species. Pituitary injections are widely used in artificial breeding of sturgeon and carp fish.
The third neurosecretory section of the diencephalon. - the pineal gland. Its hormones (serotin, melatonin, adrenoglomerulo-tropin) are involved in seasonal metabolic changes. Its activity is influenced by illumination and the duration of daylight hours: with their increase, the activity of fish increases, growth accelerates, the gonads change, etc.
The thyroid gland is located in the pharynx, near the abdominal aorta. In some fish (some sharks, salmonids), it is a dense paired formation, consisting of follicles that secrete hormones, in others (perch, cyprinid) glandular cells do not form a formed organ, but lie diffusely in the connective tissue.
The secretory activity of the thyroid gland begins very early. For example, in sturgeon larvae, on the 2nd day after hatching, the iron, although not fully formed, exhibits active secretory activity, and on the 15th day, the formation of follicles almost ends. Colloid-containing follicles are found in 4-day-old stellate sturgeon larvae.
Subsequently, the gland periodically secretes the accumulating secretion, and an increase in its activity is noted in juveniles during metamorphosis, and in sexually mature fish during the pre-spawning period, before the appearance of the breeding plumage. The maximum activity coincides with the moment of ovulation.
The activity of the thyroid gland changes throughout life, gradually decreasing in the process of aging, and also depending on the supply of fish with food: underfeeding causes an increase in the function.
In females, the thyroid gland is more developed than in males, but in males it is more active.
The thyroid gland plays an important role in the regulation of metabolism, growth and differentiation processes, carbohydrate metabolism, osmoregulation, maintaining the normal activity of the nerve centers, adrenal cortex, and gonads. The addition of a thyroid preparation to the feed accelerates the development of juveniles. If the function of the thyroid gland is dysfunctional, a goiter appears.
Sex glands — The ovaries and testes secrete sex hormones. Their secretion is periodic: the greatest amount of hormones is formed during the period of maturity of the gonads. These hormones are associated with the appearance of a marriage dress.
In the ovaries of sharks and river eel, as well as in the blood plasma of sharks, the hormones 17 ^ -estradiol and esterone were found, which are localized mainly in the oocytes, less in the ovarian tissue. Deoxycorticosterone and progesterone have been found in male sharks and salmon.
In fish, there is a relationship between the pituitary gland, the thyroid gland, and the gonads. In the pre-spawning and spawning periods, the maturation of the gonads is directed by the activity of the pituitary gland and the thyroid gland, and the activity of these glands is also interrelated.
The pancreas in teleost fish performs a double function — the glands of external (secretion of enzymes) and internal (secretion of insulin) secretion.
Insulin production is localized in the islets of Langerhans interspersed with liver tissue. It plays an important role in the regulation of carbohydrate metabolism and protein synthesis.
Ultimobranchial (supraperibranchial, or subesophageal) glands are found in both marine and freshwater fish. These are paired or unpaired formations lying, for example, in pikes and salmonids, on the sides of the esophagus. Glandular cells secrete the hormone calcitonin, which prevents calcium resorption from bones and thus prevents its concentration in the blood from increasing.
Adrenal glands. In contrast to higher animals, in fish the medulla and cortex are separated and do not form a single organ. In teleost fish, they are located in different parts of the kidney. The cortical substance (corresponding to the cortical tissue of higher vertebrates) is embedded in the anterior part of the kidney and is called interrenal tissue. It contains the same substances as in other vertebrates, but the content of, for example, lipids, phospholipids, cholesterol, ascorbic acid in fish is higher.
The hormones of the cortical layer have a multifaceted effect on the vital activity of the body. So, glucocorticoids (cortisol, cortisone, 11-deoxycortisol were found in fish) and sex hormones are involved in the development of the skeleton, muscles, sexual behavior, carbohydrate metabolism. Removal of interrenal tissue leads to respiratory arrest even before cardiac arrest. Cortisol is involved in osmoregulacin.
The adrenal medulla in higher animals in fish corresponds to chromaffin tissue, the individual cells of which are scattered and kidney tissue. The hormone adrenaline secreted by them acts on the vascular and muscular systems, increases the excitability and strength of the heart's pulsation, causes the expansion and narrowing of blood vessels. An increase in the concentration of adrenaline in the blood causes anxiety.
The neurosecretory and endocrine organ in teleost fish is also the urohypophysis, which is located in the caudal region of the spinal cord and participates in osmoregulation, which has a great influence on the functioning of the kidneys.

Poisonousness and venomousness of fish

Poisonous fish have a venomous apparatus consisting of thorns and venom glands located at the base of these thorns (Mvoxocephalus scorpius during spawning) or in their grooves of thorns and grooves of fin rays (Scorpaena, Frachinus, Amiurus, Sebastes, etc.).

The strength of the action of poisons is different: from the formation of an abscess at the injection site to respiratory and cardiac disorders and death (in severe cases of Trachurus lesion). In our seas, poisonous are the sea dragon (scorpion), stargazer (sea cow), sea ruff (scorpion), stingray stingray, sea cat, prickly shark katran), sculpin, sea bass, ruff-nose, aukha (Chinese ruff), sea ​​mouse (lyre), high-beam perch.

These fish are harmless when eaten.

Fish, tissues and organs of which are poisonous in chemical composition, are poisonous and should not be eaten. They are especially abundant in the tropics. The shark Carcharinus glaucus has a poisonous liver, while the Tetradon puffer has ovaries and eggs. In our fauna, caviar and peritoneum are poisonous in the marinka Schizothorax and the osman Diptychus, in the barbel Barbus and the snort Varicorhynus, caviar has a laxative effect. The venom of poisonous fish acts on the respiratory and vasomotor centers, is not destroyed by boiling. Some fish have poisonous blood (eels Muraena, Anguilla, Conger, lamprey, tench, tuna, carp, etc.). The poisonous properties are manifested when the blood serum of these fish is injected; they disappear when heated, under the action of acids and alkalis.

Poisoning by stale fish is associated with the appearance in it of poisonous waste products of putrefactive bacteria. The specific “fish poison” is formed in benign fish (mainly in sturgeon and white fish) as a waste product of the anaerobic bacteria Bacillus ichthyismi, which is close to B. botulinus. The effect of the poison is manifested when eating raw, including salted fish.

PHYSIOLOGY AND ECOLOGY OF FISH

The sense organs are represented in the fish on the head. through the eyes and holes olfactory capsules.

Almost all fish distinguish colors, and some species can reflexively change your own color: light stimuli are converted by the visual organs into nerve impulses that go to the pigment cells of the skin.

Pisces recognize well smells and availability flavoring substances in water; In many species, taste buds are located not only in the mouth and lips, but also on various antennae and skin outgrowths around the mouth.

On the head of the fish are seismosensory channels and electrosensitive organs that allow them to navigate in the dark or muddy water by the slightest changes in the electric field. They make up the sensory system lateral line... In many species, the lateral line is clearly visible as one or more chains of scales with small holes.

Fish have no external hearing organs (auditory openings or auricles), but well-developed inner ear allows them to hear sounds.

Breath of fish carried through rich blood vessels gills(gill petals), and some species (loach) have developed adaptations for additional breathing with atmospheric air when oxygen is deficient in the water (during frosts, high temperatures, etc.). Loaches swallow air, which then enters the bloodstream through the blood vessels and capillaries of internal organs.

Fish movements very diverse. Usually fish move with the help of undulating body bends.

Fish with a serpentine body (lamprey, eel, loach) move with the help of curves of the whole body... Their speed of movement is low (picture on the left):

(depicts changes in body position at regular intervals)

Body temperature in fish it is determined by the temperature of the surrounding water.

In relation to the water temperature, fish are divided into cold-loving (cold-water) and heat-loving (warm-water)... Some species thrive under the ice of the Arctic, and some species can freeze into the ice for several months. Tench and crucian carp endure freezing of reservoirs to the bottom. A number of species that calmly endure freezing of the surface of the reservoir are not able to reproduce if in the summer the water does not warm up to a temperature of 15-20 ° C (catfish, silver carp, carp).

For most cold-water species (whitefish, trout), water temperatures above 20 ° C are unacceptable, since oxygen content it is not enough for these fish in warm water. It is known that the solubility of gases, including oxygen, in water sharply decreases with increasing temperature. Some species easily tolerate oxygen deficiency in water over a wide temperature range (crucian carp, tench), while others live only in cold and oxygen-rich water of mountain rivers (grayling, trout).

Fish coloring can be very diverse. In almost all cases, the color of the fish plays either masking(from predators), or signaling(in gregarious species) role. The color of fish changes depending on the season, habitat and physiological state; most vividly many fish species are colored during the breeding season.

There is a concept mating coloration(mating outfit) fish. During the breeding season, in some species (roach, bream) "pearl" tubercles appear on the scales and scalp.

Fish migration

Migrations most fish are associated with a change in water bodies that differ in water salinity.

Towards salinity of water all fish can be divided into three groups: marine(live at salinity close to oceanic), freshwater(do not tolerate salinity) and brackish found both in the estuarine areas of the sea and in the lower reaches of rivers. The latter species are close to those feeding in brackish-water deltas, bays and estuaries, and spawning in rivers and floodplain lakes.

Verily freshwater fish are fish that live and breed only in fresh water (gudgeon).

A number of species, usually living in sea or fresh water, can easily move under new conditions to "atypical" water for themselves. So, some gobies and sea needles have spread along the rivers and reservoirs of our southern rivers.

A separate group is formed by anadromous fish spending most of their lives in the sea (feeding and maturing, that is, growing in the sea), and on spawning coming into rivers or, conversely, i.e. spawning migrations from rivers to seas.

These fish include many sturgeon and salmon fish of the highest commercial value. Some species of fish (salmon) return to the water bodies where they were born (this phenomenon is called homing - the instinct at home). These abilities of salmon are actively used in the introduction of eggs into rivers that are new for these fish. The mechanisms that allow anadromous fish to unmistakably find their native river or lake are unknown.

There are species that live most of their life in rivers, and go to the sea for spawning (i.e. vice versa). Among our fauna, such travels are made by the river eel, which lives and matures in rivers and lakes, and goes to the Atlantic Ocean to continue the genus.

In anadromous fish, when passing from one environment to another, noticeably metabolism changes(most often, when the genital products mature, they stop eating) and appearance(body shape, coloration, etc.). Often these changes are irreversible - many species after spawning perish.

Pink salmon, or pink salmon (Oncorhynchus gorbuscha) in different life phases
(male and female during breeding season and oceanic phase)

An intermediate ecological group is formed by semi-anadromous fish- fish breeding in fresh water, and leaving for feeding desalinated areas of the sea - the coastal zone of the seas, bays, estuaries.

Reproduction of fish

Spawning- the most important stage in the life of fish.

Many fish don't care about caviar and sprinkle a huge number of eggs (in beluga up to several million) into the water, where they are fertilized. A huge number of eggs perish, and one, rarely two individuals survive from each female. Here, the astronomical number of spawned eggs is responsible for the preservation of the species.

Some species of fish (gobies, sticklebacks) spawn up to a hundred eggs, but guard offspring, build peculiar nests, protect eggs and fry. There are even species, such as tilapia, that hatch eggs and larvae. in the mouth... The number of eggs in these fish is small, but the survival rate is significantly higher, which ensures the preservation of the species.

Spawning site in most spawning fish it is characteristic of the species, in connection with which there is their division into environmental groups by the nature of spawning:

• pelagophiles spawn in the water column, most often along the current, where it develops (in suspension);
• lithophiles lay eggs on the ground;
• phytophils - for aquatic vegetation.
• there are a few species that have found an extremely original substrate for their eggs: for example, bitters lay eggs in the mantle cavity of bivalve mollusks.

Fish nutrition

Fish eating habits can vary greatly. with age... Usually juveniles are planktophagous or benthophagous, and with age they turn to predation. For example fry