The structure and physiological characteristics of fish

table of contents

Body shape and methods of movement

The skin of fish

Digestive system

Respiratory system and gas exchange (New)

Circulatory system

Nervous system and sense organs

Endocrine glands

Poisonousness and poisonousness 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 opportunity to move in water (an environment much denser than air) with the least expenditure of energy 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 body without protrusions, covered with mucus, facilitates movement; no neck; a pointed head with pressed gill covers and clenched jaws cuts through the water; the fin system determines the movement in the right direction. Up to 12 allocated according to lifestyle various types body shape

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

Arrow-shaped - the bones of the snout are elongated and pointed, the body of the fish has the same height along the entire length, the dorsal fin is related to the caudal and is located above the anal, which creates an imitation of the plumage of an arrow. This form is typical for fish that do not travel long distances, stay in ambush and develop high speeds of movement for a short period of time due to the push of the fins when throwing at prey or avoiding a predator. These are pikes (Esox), garfish (Belone), etc. Torpedo-shaped (it is often called spindle-shaped) - characterized by a pointed head, rounded, oval-shaped body in cross section, thinned caudal peduncle, often with additional fins. It is characteristic of good swimmers capable of long-term movements - tuna, salmon, mackerel, sharks, etc. These fish are able to swim for a long time, so to speak, at a cruising speed of 18 km per hour. Salmon are capable of jumping two to three meters 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 is symmetrically compressed laterally - strongly laterally compressed, high with a relatively short length and high. These are fish of coral reefs - bristle teeth (Chaetodon), thickets of bottom vegetation - angelfish (Pterophyllum). This body shape helps them to easily maneuver among obstacles. Some pelagic fish also have a symmetrically laterally compressed body shape, which needs to quickly change position in space to disorientate predators. The moonfish (Mola mola L.) and bream (Abramis brama L.) have the same body shape. The body is asymmetrically compressed from the sides - the eyes are shifted to one side, which creates an asymmetry of the body. It is characteristic of demersal sedentary fish of the Flounder-like order, helping them to camouflage themselves well at the bottom. In the movement of these fish, an important role is played by the wavy bending of the long dorsal and anal fins. Flattened in the dorsoventral direction, the body is strongly compressed in the dorsal-abdominal direction, as a rule, the pectoral fins are well developed. Sedentary bottom fish have this body shape - most rays (Batomorpha), angler(Lophius piscatorius L.). The flattened body camouflages the fish in bottom conditions, and the eyes located on top help to see the prey. Eel-shaped - the body of the fish is elongated, rounded, having the appearance of an oval in a cross section. The dorsal and anal fins are long, there are no pelvic fins, and the caudal fin is small. It is characteristic of bottom and bottom fish, such as eels (Anguilliformes), which move by bending their bodies laterally. Ribbon-shaped - the body of the fish is elongated, but unlike the eel-shaped form, it is strongly compressed from the sides, which provides a large specific surface area and allows the fish to live in the water column. The nature of their movement is the same as that of eel-shaped fish. This body shape is typical for saber fish (Trichiuridae), herring king (Regalecus). Macro-shaped - the body of the fish is high in the front, 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 - macrourus-like (Macrurus), chimeric (Chimaeriformes). Asterolepid (or body-shaped) - the body is enclosed in a bony shell, which provides protection from predators. This body shape is characteristic of benthic inhabitants, many of which are found in coral reefs, for example for boxcars (Ostracion). The spherical shape is characteristic of some species from the Tetraodontiformes order - the ball fish (Sphaeroides), the hedgehog fish (Diodon), etc. These fish are poor swimmers and move with the help of undulating (wave-like) movements of the fins over short distances. When threatened, fish inflate the intestinal air sacs, filling them with water or air; at the same time, the spikes and spines on the body are straightened, protecting them from predators. The needle-shaped body shape is characteristic of marine needles (Syngnathus). Their elongated body, hidden in a bone shell, imitates the leaves of the zoster, in the thickets of which they live. Fish lack lateral mobility and move with the help of the undulating (wave-like) action of the dorsal fin. Often there are fish whose body shape resembles simultaneously different types of forms. To eliminate the unmasking shadow on the belly of the fish that occurs when illuminated from above, small pelagic fish, such as herring (Clupeidae), sabrefish (Pelecus cultratus (L.)], have a pointed, laterally compressed abdomen with a sharp keel. Large mobile pelagic predators have mackerel (Scomber), swordfish (Xiphias gladius L.), tuna (Thunnus) - usually do not develop a keel.Their method of defense is speed of movement, not camouflage.In bottom fish, the cross-sectional shape approaches an isosceles trapezium facing large base down, which eliminates the appearance of shadows on the sides when illuminated from above.Therefore, most demersal fish have a wide flattened body.

SKIN, SCALES AND LUMINOSIS

Rice. Fish scale shape. a - placoid; b - ganoid; c - cycloid; d - ctenoid

Placoid - the most ancient, preserved in cartilaginous fish (sharks, rays). It consists of a plate on which a spine rises. Old scales are discarded, new ones appear in their place. Ganoid - mainly in fossil fish. The scales are rhombic in shape, closely articulated with each other, so that the body is enclosed in a shell. Scales do not change over time. The scales owe their name to ganoin (dentine-like substance), which lies in a thick layer on the bone plate. Among modern fish armored pikes and multifeathers have it. In addition, sturgeons have it in the form of plates on the upper lobe of the caudal fin (fulcra) and scutes scattered over the body (a modification of several merged ganoid scales). Gradually changing, the scales lost ganoin. Modern bony fish it is no longer there, and the scales consist of bone plates (bone scales). These scales can be cycloid - rounded, with smooth edges (cyprinids) and ctenoid with a serrated trailing edge (percids). 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 scales, and females have cycloid scales (flounders of the genus Liopsetta), or even scales of both forms are found in one individual. The size and thickness of the scales in fish vary greatly - from microscopic scales of an ordinary eel to very large, palm-sized scales of a three-meter long barbel that lives in Indian rivers. Only a few fish do not have scales. In some, it merged into a solid, immovable shell, like a boxfish, or formed rows of closely connected bone plates, like seahorses. Bone scales, like ganoid scales, are permanent, 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 thin layers than the summer one, so it is darker than the summer one. By the number of summer and winter layers on the scales, one can determine the age of some fish. Under the scales, many fish have silvery crystals of guanine. Washed from scales, they are a valuable substance for obtaining artificial pearls. Glue is made from fish scales. On the sides of the body of many fish, one can observe a number of prominent scales with holes that form the lateral line - one of the most important sense organs. The amount of scales in the lateral line - In the unicellular glands of the skin, pheromones are formed - volatile (odorous) substances secreted in environment and acting on the receptors of other fish. They are specific to different types, even closely related; 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 announcing danger. Fish skin regenerates quickly. Through it, on the one hand, a partial release final products metabolism, and on the other hand, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play an important role in life). The skin also plays an important role as a receptor surface: it contains thermo-, baro-, chemo- and other receptors. In the thickness of the corium, the integumentary bones of the skull and pectoral fin belts are formed. Through the muscle fibers of the myomers connected to its inner surface, the skin participates in the work of the trunk and 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 isolated. 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 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). This muscle is divided by a longitudinal connective tissue layer into dorsal (upper) and abdominal (lower) parts.

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

1 - myomers, 2 - myosepts

The lateral muscles are divided by myosepts into myomers, 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 caudal section of the body and change the position of the caudal fin, due to which the body moves forward. Above the large lateral muscle along the body between the shoulder girdle and tail in sturgeons and teleosts lies the rectus lateral superficial muscle (m. rectus lateralis, m. lateralis superficialis). In salmon, a lot of fat is deposited in it. The rectus abdominis (m. rectus abdominalis) stretches along the underside of the body; some fish, such as eels, do not. Between it and the direct lateral superficial muscle are oblique muscles (m. obliguus). The muscle groups of the head control the movements of the jaw and gill apparatus (visceral muscles). The 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 excited involuntarily.

A distinction is made between striated (acting largely voluntarily) and smooth muscles (which act independently of the will of the animal). The striated muscles include the skeletal muscles of the body (trunk) and the muscles of the heart. Trunk muscles can contract quickly and strongly, but soon get tired. A feature of the structure of the heart muscles is not the parallel arrangement of isolated fibers, but the branching of their tips and the transition from one bundle to another, which determines the continuous operation of this organ. Smooth muscles also consist of fibers, but much shorter and do not exhibit transverse striation. These are the muscles of the internal organs and the walls of blood vessels, which have peripheral (sympathetic) innervation. Striated fibers, and therefore muscles, are divided into red and white, which differ, as the name implies, in color. The color is due to the presence of myoglobin, a protein that readily binds oxygen. Myoglobin provides respiratory phosphorylation, accompanied by the release of a large amount of energy. Red and white fibers are different in a number of morphophysiological characteristics: color, shape, mechanical and biochemical properties (respiratory rate, glycogen content, etc.). Red muscle fibers (m. lateralis superficialis) - 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; accumulations of fat and glycogen were found in them. Their excitability is less, individual contractions last longer, but proceed more slowly; oxidative, phosphorus and carbohydrate metabolism is more intense than in whites. The heart muscle (red) has little glycogen and a lot of enzymes of aerobic metabolism (oxidative metabolism). It is characterized by a moderate rate of contractions and tires more slowly than white muscles. In wide, thicker, light white fibers m. lateralis magnus myoglobin is small, they have less glycogen and respiratory enzymes. Carbohydrate metabolism occurs predominantly anaerobically, and the amount of energy released is less. Individual cuts are fast. Muscles contract and fatigue faster than red ones. They lie deeper. The red muscles are constantly active. They ensure long-term and uninterrupted functioning of the organs, support the constant movement of the pectoral fins, ensure the bending of the body when swimming and turning, and the continuous work of the heart. With fast movement, throws, white muscles are active, with slow movement, 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 that are characterized by long migrations, in addition to the red lateral muscles, there are additional red fibers in the white muscles. The bulk of the muscle tissue in fish is made up of 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 muscles contain more fat, while white muscles contain 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 detention. For example, in a 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 main share of fish meat . The yield of meat as a percentage of the total body weight (meatiness) is not the same for different species, and for individuals of the same species it varies depending on sex, conditions of detention, etc. Fish meat is digested faster than the meat of warm-blooded animals. It is often colorless (perch) or has shades (orange in salmon, yellowish in sturgeon, etc.), depending on the presence of various fats and carotenoids. The bulk of fish muscle proteins are albumins and globulins (85%), in total, 4 ... 7 protein fractions are isolated from different fish. The chemical composition of meat (water, fats, proteins, minerals) is different not only in different species, but also in different parts body. In fish of the same species, the amount and chemical composition of meat depend on the nutritional conditions and the physiological state of the fish. During the spawning period, especially in migratory 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 reduced by more than two times; fat and nitrogenous substances practically disappear from the muscles - the fish loses up to 98.4% of fat and 57% of protein. Features of the environment (primarily food and water) can greatly change the nutritional value of fish: in swampy, muddy or oil-polluted water bodies, fish have meat with an unpleasant odor. The quality of 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 one can judge the content of full-fledged muscle proteins in the muscles (compared to defective proteins of the connective tissue layer). This ratio varies depending on the physiological state of the fish and environmental factors. In the muscle proteins of bony fish, proteins account for: sarcoplasms 20 ... 30%, myofibrils - 60 ... 70, stroma - about 2%. All the variety of body movements is provided by the work of the muscular system. It mainly provides the release of heat and electricity in the body of the fish. An electric current is formed when a nerve impulse is conducted along a nerve, with a contraction of myofibrils, irritation of photosensitive cells, mechanochemoreceptors, etc. Electric organs

Electric organs are peculiarly altered muscles. These organs develop from the rudiments of striated muscles and are located on the sides of the fish body. They consist of many muscle plates (there are about 6000 in electric eel), converted into electrical plates (electrocytes), interbedded with gelatinous connective tissue. The bottom of the plate is negatively charged, the top 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 overseas reservoirs 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 the sea fox stingray - on the tail, in the electric catfish - on the sides. By generating electric current and perceiving lines of force distorted by objects encountered on the way, fish orient themselves in the stream, detect obstacles or prey from a distance of several meters, even muddy water. In accordance with the ability to generate electric fields, fish are divided into three groups: 1. Strongly electric species - they have large electric 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 stingray, electric catfish). 2. Weakly electric species - they have small electric organs that generate discharges with a voltage of less than 17 V. The main purpose of the discharges is location, signaling, orientation (many mormirids, hymnotids, and some rays that live in the muddy rivers of Africa). 3. Non-electric species - do not have specialized organs, but have electrical activity. The discharges generated by them extend 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, sable, perch, etc.).

PHYSIOLOGY AND ECOLOGY OF FISH

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

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

Fish are good at recognizing smells and availability flavor substances in water; in many species, taste buds are located not only in the oral cavity and on the 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 sideline. In many species, the lateral line is clearly visible as one or more chains of scales with small holes.

Fish don't have external bodies hearing (auditory openings or auricles), but well developed inner ear allows them to hear sounds.

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

Fish movements very varied. Fish usually move by undulating body curves.

Fish with a serpentine body shape (lamprey, eel, loach) move with the help of whole body curves. The speed of their movement is small (figure on the left):


(depicted changes in body position at certain intervals of time)

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

In relation to water temperature, fish are divided into cold-loving (cold-water) And heat-loving (warm-water). Some species thrive under the Arctic ice, 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 the freezing of the surface of a reservoir are not able to breed if the water does not warm up to a temperature of 15-20 ° C in summer (catfish, silver carp, carp).

For most cold-water species (whitefish, trout), water temperatures above 20 ° C are unacceptable, since oxygen content V warm water not enough for these fish. 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 the cold and oxygen-rich water of mountain streams (grayling, trout).

Fish coloring may be the most varied. In almost all cases, the coloration of fish plays either masking(from predators), or signaling(in schooling species) role. The color of fish varies depending on the season, habitat conditions and physiological state; Many fish species are most brightly colored during the breeding season.

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

Fish migrations

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

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

Truly 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 spread along the rivers and reservoirs of our southern rivers.

A separate group is formed anadromous fish, who spend most of their lives in the sea (feeding and maturing, that is, growing in the sea), and on spawning coming to the rivers or vice versa, i.e. making spawning migrations from rivers to seas.

These fish include many of the most commercially valuable sturgeon and salmon fish. Some species of fish (salmon) return to the waters where they were born (this phenomenon is called homing - the instinct of the house). These abilities of salmon are actively used when introducing caviar into rivers new for these fish. The mechanisms that allow migratory fish to accurately locate their native river or lake are unknown.

There are species that live most of their lives in rivers, and go to the sea to spawn (i.e. vice versa). Among our fauna, such journeys are made by the river eel, living and maturing in rivers and lakes, and leaving for the Atlantic Ocean to procreate.

In anadromous fish, when moving from one environment to another, it is noticeable metabolism changes(most often when the reproductive products mature, they stop feeding) 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)

The intermediate ecological group is formed by semi-anadromous fish- fish that breed in fresh water, and for feeding go to desalinated areas of the sea - the coastal zone of the seas, bays, estuaries.

fish breeding

Spawning - milestone in the life of fish.

many fish don't care about caviar and sweep great amount eggs (in beluga up to several million) into the water, where their fertilization takes place. A huge number of eggs perish, and from each female one, rarely two individuals survive. Here, the astronomical number of spawned eggs is responsible for the preservation of the species.

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

spawning place in most spawning fish, it is characteristic of the species, and therefore there is their division into environmental groups according to the nature of spawning:

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

Fish nutrition

The nature of fish feeding can vary greatly. with age. Usually, juveniles are planktivorous or benthivorous, and with age they switch to predation. For example, fry

Optimal development temperatures can be determined by estimating the intensity of metabolic processes at individual stages (with strict morphological control) by changing oxygen consumption as an indicator of the rate metabolic reactions at different temperatures. The minimum oxygen consumption for a certain stage of development will correspond to the optimal temperature.

Factors affecting the process of incubation, and the possibility of their regulation.

Of all abiotic factors the strongest effect on fish is temperature. The temperature is very big influence on fish embryogenesis at all stages and stages of embryo development. Moreover, for each stage of embryo development, there is optimum temperature. Optimal temperatures are those temperatures at which the highest rate of metabolism (metabolism) is observed at individual stages without disturbing morphogenesis. Temperature conditions under which embryonic development takes place in vivo and at existing methods incubation of eggs almost never correspond to the maximum manifestation of valuable specific features fish useful (needed) to man.

Methods for determining the optimal temperature conditions for development in fish embryos are quite complex.

It has been established that in the process of development, the optimum temperature for spring-spawning fish increases, while for autumn-spawning it decreases.

The size of the optimal temperature zone expands as the embryo develops and reaches its largest size before hatching.

Determining the optimal temperature conditions for development allows not only improving the method of incubation (holding prelarvae, rearing larvae, and rearing juveniles), but also opens up the possibility of developing techniques and methods for directing influence on development processes, obtaining embryos with specified morphofunctional properties and specified sizes.

Consider the impact of other abiotic factors on the incubation of eggs.

The development of fish embryos occurs with the constant consumption of oxygen from the external environment and the release of carbon dioxide. A permanent excretion product of embryos is ammonia, which occurs in the body in the process of protein breakdown.

Oxygen. The ranges of oxygen concentrations within which the development of embryos of different fish species is possible differ significantly, and the oxygen concentrations corresponding to upper bounds these ranges far exceed those found in nature. Thus, for pike perch, the minimum and maximum oxygen concentrations at which the development of embryos and hatching of prelarvae still occur are 2.0 and 42.2 mg/l, respectively.



It has been established that with an increase in the oxygen content in the range from the lower lethal limit to values ​​significantly exceeding its natural content, the rate of embryo development naturally increases.

Under conditions of deficiency or excess of oxygen concentrations in embryos, there are large differences in the nature of morphofunctional changes. For example, at low oxygen concentrations the most typical anomalies are expressed in body deformation and disproportionate development and even the absence of individual organs, the appearance of hemorrhages in the area of ​​large vessels, the formation of dropsy on the body and gall sac. At elevated oxygen concentrations The most characteristic morphological disturbance in embryos is a sharp weakening or even complete suppression of erythrocyte hematopoiesis. Thus, in pike embryos that developed at an oxygen concentration of 42–45 mg/l, by the end of embryogenesis, erythrocytes in the bloodstream disappear completely.

Along with the absence of erythrocytes, other significant defects are also observed: muscle motility stops, the ability to respond to external stimuli and get rid of the membranes is lost.

In general, embryos incubated at different oxygen concentrations differ significantly in their degree of development at hatching.

Carbon dioxide (CO). Embryonic development is possible in a very wide range of CO concentrations, and the concentrations corresponding to the upper limits of these ranges are much higher than those that embryos encounter in natural conditions. But with an excess of carbon dioxide in the water, the number of normally developing embryos decreases. In experiments, it was proved that an increase in the concentration of dioxide in water from 6.5 to 203.0 mg/l causes a decrease in the survival rate of chum salmon embryos from 86% to 2%, and at a carbon dioxide concentration of up to 243 mg/l, all embryos in the process of incubation perished.

It has also been established that the embryos of bream and other cyprinids (roach, blue bream, silver bream) develop normally at a carbon dioxide concentration in the range of 5.2-5.7 mg/l, but with an increase in its concentration to 12.1-15.4 mg /l and a decrease in concentration to 2.3-2.8 mg/l, an increased death of these fish was observed.

Thus, both a decrease and an increase in the concentration of carbon dioxide have a negative effect on the development of fish embryos, which gives grounds to consider carbon dioxide as a necessary component of development. The role of carbon dioxide in fish embryogenesis is diverse. An increase in its concentration (within the normal range) in water enhances muscle motility and its presence in the environment is necessary to maintain the level motor activity embryos, with its help, the breakdown of oxyhemoglobin of the embryo occurs and this ensures the necessary tension in the tissues, it is necessary for the formation organic compounds body.

Ammonia in bony fish, it is the main product of nitrogenous excretion both during embryogenesis and in adulthood. In water, ammonia exists in two forms: in the form of undissociated (not separated) NH molecules and in the form of ammonium ions NH. The ratio between the amount of these forms significantly depends on temperature and pH. With an increase in temperature and pH, the amount of NH increases sharply. Toxic action predominantly NH exerts on fish. The action of NH has a negative effect on fish embryos. For example, in trout and salmon embryos, ammonia causes a violation of their development: a cavity filled with a bluish liquid appears around the yolk sac, hemorrhages form in the head section, and motor activity decreases.

Ammonium ions at a concentration of 3.0 mg/l cause a slowdown in linear growth and an increase in the body weight of pink salmon embryos. At the same time, it should be borne in mind that ammonia in bony fish can be re-involved in metabolic reactions and the formation of non-toxic products.

Hydrogen indicator pH of water, in which embryos develop, should be close to the neutral level - 6.5-7.5.

water requirements. Before water is supplied to the incubation apparatus, it must be cleaned and neutralized using sedimentation tanks, coarse and fine filters, and bactericidal installations. The development of embryos can be negatively affected by the brass mesh used in the incubation apparatus, as well as fresh wood. This effect is especially pronounced if sufficient flow is not ensured. Exposure to a brass mesh (more precisely, copper and zinc ions) causes inhibition of growth and development, and reduces the vitality of embryos. Exposure to substances extracted from wood leads to dropsy and anomalies in the development of various organs.

Water flow. For the normal development of embryos, water flow is necessary. The lack of flow or its insufficiency has the same effect on embryos as a lack of oxygen and an excess of carbon dioxide. If there is no change of water at the surface of the embryos, then the diffusion of oxygen and carbon dioxide through the shell does not provide the necessary intensity of gas exchange, and the embryos experience a lack of oxygen. Despite the normal saturation of the water in the incubation apparatus. The efficiency of water exchange depends more on the circulation of water around each egg than on total incoming water and its speed in the incubation apparatus. Efficient water exchange during the incubation of eggs in a stationary state (salmon caviar) is created by water circulation perpendicular to the plane of the frames with eggs - from bottom to top with an intensity in the range of 0.6-1.6 cm/sec. This condition is fully met by the IM incubation apparatus, which imitates the conditions of water exchange in natural spawning nests.

For the incubation of beluga and stellate sturgeon embryos, the optimal water consumption is 100-500 and 50-250 ml per embryo per day, respectively. Before hatching, the prelarvae in the incubation apparatus increase the water flow in order to ensure normal conditions for gas exchange and the removal of metabolic products.

It is known that low salinity (3-7) is detrimental to pathogenic bacteria, fungi and has a beneficial effect on the development and growth of fish. In water with a salinity of 6-7, not only the waste of developing normal embryos decreases and the growth of juveniles accelerates, but also overripe eggs develop, which die in fresh water. An increased resistance of embryos developing in brackish water, to mechanical influences. Therefore, in Lately great importance acquires the question of the possibility of rearing anadromous fish in brackish water from the very beginning of their development.

The influence of light. When carrying out incubation, it is necessary to take into account the fitness of embryos and prelarvae. various kinds fish for lighting. For example, for salmon embryos, light is detrimental, so the incubation apparatus must be darkened. Incubation of sturgeon eggs in complete darkness, on the contrary, leads to a delay in development. Impact of direct sunlight causes inhibition of growth and development of sturgeon embryos and a decrease in the viability of prelarvae. This is due to the fact that sturgeon caviar under natural conditions develops in muddy water and at a considerable depth, that is, in low light. Therefore, during the artificial reproduction of sturgeons, the incubation apparatus should be protected from direct sunlight, as it can cause damage to the embryos and the appearance of freaks.

Care of eggs during incubation.

Before the start of the hatching cycle, all hatching apparatus must be repaired and disinfected with a bleach solution, rinsed with water, walls and floors washed with a 10% lime solution (milk). IN preventive purposes against the defeat of eggs with saprolegnia, it must be treated with a 0.5% formalin solution for 30-60 seconds before loading it into the incubation apparatus.

Caviar care during the incubation period consists in monitoring the temperature, oxygen concentration, carbon dioxide, pH, flow, water level, light regime, the state of the embryos; selection of dead embryos (with special tweezers, screens, pears, siphon); preventive treatment as needed. Dead eggs are whitish in color. When salmon caviar is silted, showering is carried out. Persuasion and selection of dead embryos should be carried out during periods of reduced sensitivity.

The duration and features of the incubation of eggs of various fish species. Hatching of prelarvae in various incubators.

The duration of incubation of eggs is largely dependent on the temperature of the water. Usually, with a gradual increase in water temperature within the optimal limits for the embryogenesis of a particular species, the development of the embryo gradually accelerates, but as the temperature maximum approaches, the development rate increases less and less. At temperatures close to the upper threshold, early stages crushing of fertilized eggs, its embryogenesis, despite the increase in temperature, slows down, and with a greater increase, the death of eggs occurs.

At adverse conditions(insufficient flow, overloading of incubators, etc.) the development of incubated eggs slows down, hatching starts late and takes longer. The difference in the duration of development at the same water temperature and different flow rates and loads can reach 1/3 of the incubation period.

Features of incubation of eggs of various fish species. (sturgeon and salmon).

Sturgeon.: supply of incubation apparatus with water with oxygen saturation of 100%, carbon dioxide concentration of not more than 10 mg / l, pH - 6.5-7.5; protection from direct sunlight to avoid damage to the embryos and the appearance of malformations.

For stellate sturgeon, the optimal temperature is from 14 to 25 C, at a temperature of 29 C, the development of embryos is inhibited, at 12 C - a large death and many freaks appear.

For the sturgeon of the spring run, the optimal incubation temperature is 10-15 C (incubation at a temperature of 6-8 C leads to 100% death, and at 17-19 C many abnormal prelarvae appear.)

Salmon. The optimal level of oxygen at the optimum temperature for salmonids is 100% of saturation, the level of dioxide is not more than 10 mg / l (for pink salmon, no more than 15 is permissible, and no more than 20 mg / l), pH - 6.5-7.5; complete blackout during incubation of salmon caviar, protection of whitefish caviar from direct sunlight.

For Baltic salmon, salmon, Ladoga salmon, the optimum temperature is 3-4 C. After hatching, the optimum temperature rises to 5-6, and then to 7-8 C.

Incubation of whitefish caviar mainly occurs at a temperature of 0.1-3 C for 145-205 days, depending on the type and thermal regime.

Hatching. The duration of hatching is not constant and depends not only on temperature, gas exchange, and other incubation conditions, but also on the specific conditions (flow rate in the incubation apparatus, shocks, etc.) necessary for the release of the embryo hatching enzyme from the shells. The worse the conditions, the longer the duration of hatching.

Usually, under normal environmental conditions, the hatching of viable prelarvae from one batch of eggs is completed in sturgeon within a few hours to 1.5 days, in salmon - 3-5 days. The moment when there are already several dozen prelarvae in the incubation apparatus can be considered the beginning of the hatching period. Usually, after this, mass hatching occurs, and at the end of hatching, dead and ugly embryos remain in the shells in the apparatus.

Extended hatching periods most often indicate unfavorable environmental conditions and lead to an increase in the heterogeneity of prelarvae and an increase in their mortality. Hatching is a big inconvenience for the fish farmer, so it is important to know the following.

The hatching of the embryo from the eggs depends largely on the release of the hatching enzyme in the hatching gland. This enzyme appears in the gland after the onset of heart pulsation, then its amount rapidly increases until the last stage of embryogenesis. At this stage, the enzyme is released from the gland into the perivitelin fluid, the enzymatic activity of which sharply increases, and the activity of the gland decreases. The strength of the membranes with the appearance of the enzyme in the perivitelin fluid rapidly decreases. Moving in weakened membranes, the embryo breaks them, enters the water and becomes a prelarva. Hatching enzyme release and muscle activity, which is of paramount importance for release from the membranes, is more dependent on external conditions. They are stimulated by the improvement of aeration conditions, the movement of water, and shocks. To ensure unanimous hatching, for example, in sturgeons, the following are necessary: ​​strong flow and vigorous mixing of eggs in the incubation apparatus.

The timing of hatching of prelarvae also depends on the design of the incubation apparatus. Thus, in sturgeons, the most favorable conditions for friendly hatching are created in the sturgeon incubator, in Yushchenko's devices, the hatching of larvae is significantly extended, and even less favorable conditions for hatching are in the Sadov and Kakhanskaya trough incubators.

SUBJECT. BIOLOGICAL FOUNDATIONS FOR PRE-LARGER HOLDING, MATERIAL GROWTH AND GROWING OF YOUNG FISH.

The choice of fish-breeding equipment depending on the ecological and physiological properties of the species.

In modern technological process After the hatchery reproduction of fish, after the incubation of eggs, the holding of prelarvae, rearing of larvae and rearing of juveniles begins. Such technology system provides for complete fish-breeding control during the formation of the fish organism, when important biological transformations of the developing organism take place. For sturgeon and salmon, for example, such transformations include the formation of an organ system, growth and development, and physiological preparation for life in the sea.

In all cases, violations of environmental conditions and breeding technology associated with the lack of correct ideas about certain features of the biology of the farmed object or the mechanical use of fish farming methods of equipment and regime, without understanding the biological meaning, entail an increased death of farmed fish in the period of early ontogenesis.

One of the most critical periods of the entire biotechnical process of artificial reproduction of fish is the holding of prelarvae and rearing of larvae.

The prelarvae released from their shells go through the stage of a passive state in their development, which is characterized by low mobility. When keeping prelarvae, the adaptive features of this period of development of the given species are taken into account, and conditions are created that ensure the greatest survival before switching to active feeding. With the transition to active (exogenous) nutrition, the next link in the fish breeding process begins - rearing larvae.

Features of the life of migratory fish (part 1)

The migrations of pelagic and bottom fish take place in a more or less homogeneous environment of the sea. The fish only have to adapt somewhat to pressure differences, to different temperatures and slight changes in water salinity, but they do not have to find themselves in a completely new environment that would require a complete restructuring of the entire physiological side of life. This is not at all what we see during the migrations of anadromous fish, which for reproduction rise from the sea into rivers and reach the upper reaches of the latter. They are forced to adapt to an environment that is normal for marine fish deadly. Experiments set by Sömner (Sumner, 1906) on a number of marine fish showed that their transfer from sea ​​water in fresh water causes their death, often already in a very short time. The cause of death is a change in the osmotic pressure of the blood and cavity fluid due to the extraction of the surrounding fresh water salt from the body of the fish. The gills are primarily to blame for this: their thin membranes cannot resist osmosis and allow salt to pass through.
Because of this, anadromous fish, which change their environment at least twice in their lives (when young, they pass from fresh water to sea water, and when they are mature they make the reverse transition), have to develop a special ability to endure a strong decrease in salt concentration during external environment and keep the salts in your body; without passing them through the membranes. Green's experiments (Green, 1905), who determined the content of salts in the blood of Chinook salmon (Ortcorhynchus ischawytscha Walb.) by freezing blood, showed that in fish taken from the sea, the freezing point of blood is 0.762 , - 0.737°, and in fish from spawning in the upper reaches of the river - 0.628°, which indicates a decrease in the concentration of salts in the blood of fish by only one fifth. How this ability is achieved only slightly to lower the concentration of salts in body fluids, we do not know, but migratory fish have this ability to a high degree.
In addition to a sharp decrease in salt concentration, anadromous fish have to adapt to the fast and strong flow of rivers that counteract their movement, to completely different conditions of water temperature, to a different content of gases in it, to a different transparency; one has to develop a whole series of new instincts connected with life in the river, with overcoming various obstacles along the way and with avoiding dangers. Absolutely amazing and incomprehensible to us is the guiding instinct, thanks to which migratory fish find not only the same river in which they hatched, but also the same tributary of it and even supposedly the same spawning ground, as at least some observers claim. .