Fish and their habitat. Superclass Pisces. External building. Abiotic factors of water bodies

It is impossible to describe all the innumerable habitats of fish, ranging from small streams and ponds to vast oceans. Therefore, we are forced to limit ourselves to three main types of fish ecosystems: lakes, streams and seas. In addition, there are many intermediate fish habitats, which we do not dwell on. Our main focus now is on the geographical zones with a temperate climate.

lakes

Lakes can be classified different ways. Here we rely on their ability to reproduce organic matter. Oligotrophic lakes, poor in nutrients, are relatively deep and contain few living organisms. Nutrient-rich, rather shallow eutrophic lakes are a source of rich organic life.

The productivity of a lake is determined primarily by its basin, i.e. the place of catchment or collection of precipitation, as well as climate. As a rule, the majority of oligotrophic lakes are located in areas with insignificant ancient stone deposits, and the main number of eutrophic lakes are located in regions rich in limestone. Lakes in densely populated parts of the Western world are becoming increasingly eutrophic, constantly receiving nutrients from municipal and farm runoff. This ever-increasing influx of nutrients, as we shall soon see, is a serious threat to salmonids, although at present such conditions are quite suitable for the so-called eutrophic species, mainly the numerous cyprinids (cyprionids).

life in the lake

The life of animals and vegetation in the lake largely depends on the presence of food in it. Both the number and diversity of living organisms differ significantly in eutrophic and oligotrophic lakes. However, both these types of lakes have common biotic features.

Plankton - this is a large group of tiny organisms floating in the water, whose movement is more or less dependent on the current. To a greater extent, this applies to plant species (phytoplankton), while its animal species (zooplankton) are more active swimmers. Most zooplankton live in free waters lakes, which are called the pelagic zone. Some of them, such as copepods and cladocerans, make vertical diurnal migrations, rising to the surface of the water at night and returning to the depths during the day. This phenomenon of migration has not yet been explained, but is probably related to sunlight. As we will see, plankton is the main food for almost all juvenile fish, as well as for many species of adult fish.

Nekton usually includes floating organisms, in particular the strongest of them, which can change the direction of their swimming at will. These are mainly fish, of course, as well as some other organisms, such as crustaceans and waterfowl, which are also classified as nekton.

Benthos - is a group of organisms that live or rest on the bottom. They live in bottom sediments or are connected with the bottom by some other conditions of their life or nutrition. In the coastal zone of lakes, the environment is very diverse, intense and requires special adaptation. For example, species living in areas of steep, wind-blown, rocky bottom must be able to withstand mechanical pressure. Like many river animals, they often have a fairly flat body, and sometimes claws, suckers, or rough pads on their limbs. In contrast, individuals living in a calm lagoon with a clay or mud bottom can be quite fragile. They only need to breathe in enough oxygen to make up for the lack of it often found in such places. Due to photosynthesis, such a protected environment is usually highly productive in terms of vegetation. Its benthos is often very diverse and includes worms, molluscs, crustaceans and insects in various stages of development.

The coastal zone of the lake is the richest in species diversity. If you move in depth, the number of species is reduced due to the greater impoverishment of the habitat.

In a eutrophic lake, the benthos consists mainly of root vegetation in the coastal zone. The shallows of this zone are inhabited by heliophytes - light-loving vegetation with long stems, their upper part directed towards the surface. Next to them there are root plants with floating leaves, whose flowers barely reach the surface of the water. Next are bottom root plants, completely hidden under water. This deep-water vegetation is not usually found in eutrophic lakes, but has great importance for oligotrophic water bodies.

Food chains in the lake

The main food producers in lakes are green algae. With the help of their chlorophyll, they produce nutrients through photosynthesis from solar energy, carbon dioxide and water. In a sense, they feed themselves, but still depend on feeding from outside. Among other things, they need bacteria to decompose dead matter and thus provide them with their staple food. Therefore, bacteria should be considered as the basis of the food "web" in lakes.

Green algae represent the first cell of this network. They are followed by herbivorous animals - the main consumers who have to choose between living and dead plant materials. What they prefer, we almost do not know. Herbivorous organisms living at such depths, where there is not enough sunlight for the growth of green algae, must naturally feed on dead substances that fall there from the surface. They may also form the main diet of herbivorous organisms in the coastal zone.

Food chains in temperate lake climate zone. These chains do not have to lead from primary consumers to final ones. Due to their close interrelationships, they often form a complex food chain in their environment.

a detritus
b mayfly larvae
With coastal algae
d phytoplankton
e coastal plants
f shellfish
g rotifers
h cyclops
i daphnia
j water donkey
k bloodworm
l freshwater snails
m horseleech
n mayfly
O perch fry
R trout
q perch
r Pike

The third cell of the food web is made up of carnivores that devour herbivores. Other animals feed on them, mainly fish, which represent the fourth cell, and so on. Any simple sequence of organisms within this network is already a food chain, but the diet of most organisms covers several food chains, which are sometimes intertwined in a complex way into a very confusing food web. This pattern may also change over time: for example, in young age most fish feed on zooplankton, then switch to bottom dwellers, and some of them, like carp, can feed on algae already in adulthood.

Where does the fish live in the lake?

Fish occupy almost all habitat niches, or biotopes, of the lake, but the main number of species and individuals is located in the coastal zone. Naturally, plankton-eating fish such as whitefish, which live mainly in pelagic waters, are much less attached to the coastal zone than, for example, trout, whose main source of food is located there.

The figure shows a "fictitious" lake, on which the most likely habitats of fish are marked: (a) confluence of a stream, river, (b) swampy shore, (c) cape, (d) source of a stream, river, (e) overhanging trees, (f) boulders on the bottom.

As in the sea, the habitats of fish in the lake are determined by many factors. The temperature of the water is often of great importance. This forces fish such as pike, which are relatively well adapted to cold water, stay in shallow waters in spring and autumn, but move to cooler, deeper waters in summer. It is said that perch loves warmth and stays in the warmest places or layers of water in all seasons, even if the temperature difference is only a few tenths of a degree.

It is said that trout lives mainly in the coastal zone, and we are sure to find them there at any time of the year, unless, of course, our definition of this zone is too narrow.

Flowing reservoirs

Depending on the size and volume, water flows are divided into streams, rivers and rivers. From the point of view of the speed of the water flow, they are classified into backwaters, rapids, waterfalls, etc. A backwater is a section of more or less stagnant water between streams or fast streams. We also distinguish upstream stream or waterfall, indicating its beginning, and the lower
flow is the end.

The area from which water flows into a river is called catchment area. Watershed - these are elevations separating different watershed areas. The volume of water flowing per unit of time through any section of the waterway is known as water consumption. It is usually measured in cubic meters (thousands of liters) per second. The flow of water per unit of catchment area is called river flow, usually measured in liters per second per square kilometer. Water level - this is the height of the water surface in relation to a particular mark and is measured with a special tool with a centimeter scale.

Life in the water

As mentioned above, in lakes the role of the primary producer belongs to plankton. However, the water flow creates far from the most favorable conditions for the existence of these drifting organisms. The plankton found here is usually brought by water from lakes or slowly flowing (stagnant) reservoirs.

In fast water currents, green vegetation mainly consists of mosses, lichens and algae that cover the rocks at the bottom. Only in calm sections of streams or rivers can more developed aquatic plants be found that affect primary reproduction.

Despite this, this process may be even more intense than in any other known ecosystem. The reason for this phenomenon lies in the fact that the flow of water constantly brings the substances necessary for these organisms and carries away their decay products. This efficient exchange allows these organisms to produce much more than one would expect.

At the same time, the water flow creates extreme and stressful conditions, to which various organisms often have to adapt. The flattened bodies and claws that enable insect larvae to hold on to the rough surface of the rocks are far more important here than on their lakeside counterparts. Many larvae of riverine insects, such as stoneflies, have flattened bodies, although it is not known for sure whether this is due to adaptation to water pressure or the need to hide in cracks to escape the water flow.

Rivers temperate zone originate high in the mountains and run to the seas, where fresh water mixes with salt. (1) Cold and oxygenated spring water flows down an often rather rocky channel. Animals have adapted to these conditions: they swim well, like salmon and trout, skillfully use areas of calm water, like a goby, etc. the bottom is sometimes covered with sand and gravel.
(3) In the lower half of the river, the bottom is mostly covered with sand and gravel, and the current is much slower. Perch and eel are often found here. (4) In its lower course, the river resembles rather a pond, where cloudy water flows slowly along the muddy bottom. There is a wide variety of plant and animal life around. Most fish move slowly and have a high body profile, such as the carp and the most famous predator, the pike.

Among other adaptive changes in animals that are at risk of being swept away by a fast current, one can name a reduction in the size of protruding body parts, as, for example, in mayfly larvae. Some species of articulated animals are held in place by secretions secreted by the salivary glands. The risk of being washed away by water can also be reduced by weight or load, as some larvae make their own "houses" out of sand and pieces of gravel. Fish also adapt to the strong pressure of the water flow, so species living in the rapids usually have the most streamlined body shapes.

Demolition of organics

The drift of living and dead organic materials in the flow of water is known as organic drift. It is a mixture of insects and their larvae that have fallen to the surface of the water, plankton washed away from lakes, organisms carried away from the bottom, etc. These organic substances are partially consumed by a certain type of organisms, which are called filterers. They obtain food from drifting fauna using various trapping devices. Quite simple in some species, in others they can be quite complex, such as networks with such small cells that they can even trap bacteria! The greatest drift of organics usually occurs from lakes and other slow-flowing water bodies. There are also observed the maximum number of filter feeders and, accordingly, more crustacean predators that feed on them. Thus, demolition, filter feeders and predators "together" form a food chain that is as efficient as a factory. Particles of nutrients contained in the water, as a rule, are too small to interest the fish, are retained by filter feeders, and when they break away from the bottom, they accumulate in predators.

On the diagram of a section of the river and its sections with different currents, places of usual accumulation of fish are marked: (a) deep creek, (b) weak surface current, (c) calm area of ​​the surface, (d) fast bottom current, (e) fast flowing shallow, (f) beginning of flow with calm flow.

Since this process occurs mainly at the outlets of lakes, these sections of the watercourses are very productive and are popular with fish and, of course, anglers. In fact, many river fish use this drift in the same way as filter feeders. Instead of chasing prey, they choose a strategically advantageous place in the stream and grab everything that swims by. Such behavior in the water flow is characteristic, for example, of young salmon, river and rainbow trout, as well as, to some extent, grayling and char.

Fish habitats in water streams

Most species can be found in streams freshwater fish. Many of them live in both lakes and rivers. Moreover, all these fish live in their own specific territory.

Some fish that live in fast (flowing) streams are anatomically adapted to them. As a rule, they have a rather streamlined body. Salmonids, such as trout and grayling, are adapted to fast current in many respects, although grayling generally prefers quieter areas than trout, which resemble salmon in their habits. Other species, such as gobies and catfish, stick to the bottom, seek shelter behind or under stones. Cyprinids and pikes usually live in the calmer areas of rivers and streams.

The habitats of fish in running water are not determined by any strict rules, since the species themselves and their ability to adapt create a lot of variation. The possible habitats of trout in sections of the river with different flow rates are shown below.

Food chains in the sea resemble those in continental lakes, but are more dependent on plant photosynthesis. Here, numerous food chains are also intertwined and form a complex food pyramid. Zooplankton is of great importance for nutrition.

a detritus
b brown seaweed
With phytoplankton
d mussels
e scallop
f bivalves
g sea ​​snails
h- P zooplankton
O crabs
R sea ​​stars
q flounder
r shrimp
s herring
t gobies
and cod
v shark

Sea

Due to the vast area of ​​the world's oceans and its average depth of approximately 3800 meters, marine organisms have much more living space than their mainland counterparts, usually limited to their habitat. Yet the marine life is comparatively species-poor: about 160,000 of the million species of animals known on earth live in the seas, two-thirds of which are insects that you will not find in the sea.

As in lakes, different zones are distinguished in the seas.
Pelagic zone The open water space is practically subdivided into two zones, or regions. Neritic(coastal) zone including waters continental shelf to depths of about 200 meters, beyond which begins oceanic the zone, roughly speaking, corresponds to the coastal zone of lakes. The greatest diversity of the environment is characteristic of the neritic zone with its coasts, areas overgrown with seaweed, estuaries, shoals and coral reefs. southern seas etc., as well as numerous species and varieties of fish.

sea ​​life

Animals and plants found exclusively in the pelagic zone - among them about 200 species of animals and almost all microscopic algae - are biologists holopelagic types. Organisms that live primarily in the pelagic zone but spend some of their life stages on the bottom of the benthic zones are called meropelaginian. This group includes about 1000 species of animals such as jellyfish.

Between meropelagic animals and real ones benthic species many transitional forms. For example, adult herring live in pelagic conditions, but the eggs laid by them mature at the bottom. Cod spawn in pelagic waters but lead a benthic life. Even flounder and other flatfish initially develop in the pelagic zone. This is where most benthic marine animals go through the embryonic stage of their development.

Marine organisms, like lake organisms, are divided into plankton and nekton. Almost all primary reproduction in the sea depends on phytoplankton (algae). The most important type of phytoplankton, in addition to diatoms, are flagellates. They also live in lakes and provide one of the main types of microscopic food for crustaceans, which, in turn, feed on herring. Flagellates are famous for appearing in huge numbers, especially in tropical seas, where their brown-red shells color large areas of the water and form the so-called "red current".

The main marine zooplankton are crustaceans such as copepods. Calanus finmarchicus. This is probably the main type of animal food on earth, living in almost all oceans, from their surface to a depth of 3000 meters. In addition, this krill is an excellent filter feeder of microscopic algae, and therefore is of paramount importance as a source of nutrition in the sea. Marine nekton is made up of fish, cephalopods(squid, octopus, cuttlefish), mammals and birds.

Various habitats of marine animals along this coast have been created by the movement of wind and water. Three main types can be distinguished among them. (1) A rocky shore made up of rocks, large stones, and gravel, against which waves crash. It provides various, depending on the depth, habitat niches for plants, fish and other animals.

(2) On shallow beaches subject to constant tidal action, animal life must be adapted to the harsh conditions associated with long dry periods or land-blown winds.

(3) A little further, near the mouth of the river, the environment is more protected, and the beaches are often covered with sand or clay with small inclusions of stones.

While the number of pelagic species of marine animals is only about 3000, there are about 3000 benthic species.
150,000. They live mainly in coastal areas at depths of up to 200 meters. The diversity of life forms in the seas of the Arctic and Antarctic is much poorer than in the tropical seas. This distribution of species is largely determined by temperature, which in turn depends on geographical latitude and large ocean currents.

Fish habitats in the sea

Marine organisms seem to have an unlimited ability to adapt to their environment. Fish are found at almost all depths, although the number of their species and individuals is much larger in coastal waters. This area provides them big choice conditions from coastal areas, seagrass beds and estuaries to shallow seas. specific habitats marine fish depend, in particular, on the depth, salinity of the water, the current and the structure of the bottom (substratum). The clearest examples of this are the flounder, whose body has adapted to a bottom lifestyle, or mackerel and tuna, whose torpedo-shaped bodies allow them to develop great speed and dive to great depths. In general, the habitats of marine animals in the coastal zone can be divided into coastal waters and waters washing islands and reefs in the open sea. A typical example of the first option is shown in the accompanying illustration.

Pisces class- This is the most numerous group of modern vertebrates, which unites more than 25 thousand species. Fish are inhabitants of the aquatic environment, they breathe with gills and move with the help of fins. Fish are common in different corners planets: from high-altitude reservoirs to ocean depths, from polar waters to equatorial ones. These animals inhabit the salty waters of the seas, are found in brackish lagoons and estuaries. major rivers. They live in fresh rivers, streams, lakes and swamps.

The external structure of the fish

The main elements of the external structure of the body of the fish are: head, gill cover, pectoral fin, ventral fin, torso, dorsal fins, lateral line, caudal fin, tail and anal fin, this can be seen in the figure below.

The internal structure of fish

The figure below shows the main systems internal structure fishes

Fish Class Classification

Currently living fish are divided into 2 main classes: cartilaginous fish and bony fish. Important distinguishing features of cartilaginous fish are the presence of an internal cartilaginous skeleton, several pairs of gill slits that open outward, and the absence of a swim bladder. Almost all modern cartilaginous fish live in the seas. The most common among them are sharks and rays.

The vast majority of modern fish belongs to the class of bony fish. Representatives of this class have a ossified internal skeleton. A pair of external gill slits are covered with gill covers. Many bony fish have a swim bladder.

The main groups of Pisces

Ecological groups of fish

Depending on the habitats, ecological groups of fish are distinguished: freshwater, anadromous, brackish and marine.

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The source of information: Biology in tables and diagrams. / Edition 2e, - St. Petersburg: 2004.

The littoral zone is a place where there are almost no fish, since this is not yet a "full" body of water, but the border of the coast and the tidal zone. Therefore, only some fish risk entering the littoral. These include, in particular, the mudskipper, which stores water behind its cheeks and can get out even farther than the littoral, climbing trees and intertwining roots. During high tide, jumpers often sit on the branches of trees, firmly clinging to them with their fused ventral fins. There are 10-12 species of these fish, which have a head resembling that of a hippopotamus, with bulging frog eyes.

They travel overland in search of earthworms and other living creatures, crawler fish, oblong, reaching 15 cm in length. Californian gillicht gobies live without water in a damp and cool place for several days. Eels can crawl on the ground and outside the littoral, moving to other water bodies if necessary. Some fish, such as sphinx blennies, can sit on the littoral for a short time when thrown out by the tide, waiting for a new wave. Protopter, lepidosiren and horntooth can live for some time without water in the littoral due to the presence of special lungs. Some multifeathers can crawl out to the littoral and "travel" along it. In puddles formed by the tide, juveniles of the flag-tailed kulia prefer to stay. Only on the border of the littoral and the continental shelf is there water all the time, there are small fish like dogs, medium-sized catfish, greenfinches, needle fish, some coral fish, as well as lungfish and some cartilaginous ganoid fish.

Shallow water zone, or continental shelf

The shallow water zone, or continental shelf, is the habitat of important commercial fish: sturgeon, sprat, anchovy and many others. Herring, horse mackerel, tuna and other fish often come here in times of abundance of food. Among the small fish of temperate waters, the first place in terms of total mass is occupied by anchovies, followed by predators: cod, sharks. In this zone, fry of many species live their childhood. Atherina-grunion fish, living in flocks in the shallow water zone of Mexico and California, breed in the intertidal zone, burying their eggs in the sand at the water's edge during high tide. At low tide, the eggs develop in the warm and moist sand. In other species of atherine, the eggs have filamentous appendages, with which it is attached to some kind of substrate.

They are found among continental shelf fish and sucker fish, in which the fused ventral fins form a sucker that allows them to cling to coastal stones even during heavy seas. Live on the continental shelf and many fish that do not have a special commercial value: dogs, greenfinches, "cockerels".

In Australia, dangerous fish also live in the continental shelf zone: for example, sandy and white shark. In other places in shallow water there are sharks: hammerhead shark, herring shark, blue shark, but there are also safe species like leopard sharks and cat sharks.

Coral reefs: The zone of super-wealth of the seas

Coral reefs are a zone where all the brightest, strangest and funniest fish are gathered in one heap. On the Great Barrier Reef alone, one and a half thousand species of fish of the most diverse shapes and colors can be found, from clowns to rag-pickers.

formed Coral reefs many millions of years in small areas warm waters near the Antilles, Sunda Islands, not far from Australia, Africa, Madagascar, Sri Lanka. Tiny skeletons of coral polyps gradually layered on top of each other formed coral islands.

The reef zone is home to many planktivorous and herbivorous fish, which attract many predators, and among them a large share are cartilaginous fish.

The entire community of animals and plants of coral reefs is divided into several environmental groups. So, parrot fish, whose teeth are very similar to an arched beak, which is extremely convenient for biting off pieces of coral and algae, are destructors, that is, coral destroyers. Among other destructors, the crown of thorns starfish is widely known.

Let's talk now about the simplest of all types of relationships between fish - the predator-prey relationship. There are a lot of predators here on the reefs! This is especially true for sharks. The most common are the so-called reef sharks. There are sand, and white, and prickly, and herring sharks. There is even a carpet shark, which, like scorpions and monkfish, flat and masked by outgrowths! "Sea shadows" are always ready to grab a wounded or gaping fish. Of the stingrays, there are stingrays, a variety of electric stingrays and sawfish. But next to these dangerous fish their harmless relatives swim - manta rays (as mentioned in chapter 3, it can harm a person only if it accidentally hits a boat).

There are also bony predators. These are barracudas, and moray eels, and scorpion fish, and anglers, and groupers - there is no place to list! They can send most of their "neighbors" on the reef to a better world - except for larger fish.

I did not talk separately about the fauna of the bottom zone, since it is close in terms of fauna to the reef zone. However, there are also some interesting fish. For example, an ordinary mistake from the percops order. The way it burrows into the sand is curious: swimming head first near the bottom, it abruptly switches to reverse and, sticking its tail into the sand, quickly sinks into it completely, working with its fins. There are also many unusual species eels.

Fish are one of the most amazing aquatic animals. What features allowed them to adapt to life in these conditions? From our article you will learn about the external structure of fish and their diversity.

Habitat

No wonder about confident people They say: "Feels like a fish in water." These animals are unable to absorb oxygen from the air. Therefore, this environment is comfortable for them. The only exception is not large group lungfish. They have both gills and lungs. The latter allow them to survive unfavorable periods of drying up of water bodies and lack of oxygen.

Fish live in fresh and salt water. It depends on their type. So, gobies feel great even with an increase in salt concentration of 60%, while carp dies.

Fish are adapted to different temperatures. This indicator is also individual. The Californian Lukania prefers to live in water with a temperature of + 50. And the dahlia, which lives in shallow streams in Chukotka, freezes and thaws along with the water.

Features of the external structure of fish

Cartilaginous fish lack gill covers and a swim bladder. The respiratory organs open to the outside with independent openings. The skeleton of cartilaginous fish does not ossify. The ducts of the reproductive, digestive and excretory systems open into one opening - the cloaca.

sharks

At the mere mention of these fish, it becomes scary. Indeed, most sharks lead a predatory lifestyle. Although whale and giant shark, which are the largest representatives of the class, are quite harmless. The basis of their diet is planktonic organisms.

The body of sharks has a streamlined shape. Special meaning has a tail fin for locomotion. In most species, it is multi-lobed. It is also called heterocercal. In this case, the upper blade is much larger than the lower one.

On the elongated head in the form of a crescent is a mouth. He is surrounded large quantity teeth arranged in several rows. As some of them are erased, others grow from the inside.

Is it true that sharks are fish without scales? It's not like that at all. Although at first glance her skin seems completely naked. Shark scales are called placoid. It is the most ancient in origin. composition, form and chemical structure placoid scales resemble teeth. This is a plate with a protruding spike. Shark scales have a wide base and a flattened shape. The plates are so close to each other that the skin seems bare. In fact, it protects the body of sharks like iron chain mail.

The placoid scale performs and additional functions. It significantly reduces water resistance, which allows sharks to reach speeds of up to 80 km / h. It also allows for virtually silent movement. This is very important during hunting and attack.

stingrays

These fish have both a tail and scales. But their appearance is very unusual. Their body is flattened in the dorsal-abdominal direction. The pectoral fins of the fish are fused with the head, resembling wings. It's about about slopes.

Most of them live in the seas, but the inhabitants of fresh water are also known. Depending on the habitat, the color of the rays varies from yellowish to black. The eyes are located on the upper side of the body. There are sprinklers here as well. They represent the first pair of gill slits that open the arches of the respiratory organs.

The characteristic shape of the body is interconnected with their benthic lifestyle. Stingrays swim due to the wave-like movements of the wide pectoral fins. But most of the time they spend at the bottom. Here they burrow into the sand or wait for prey. The diet of these fish consists of small invertebrates, fish or plankton.

bony fish

This class is much more numerous. Its representatives are more than 20 thousand species. They live in all types of water bodies: from small rivers to ocean expanses.

These fish have more progressive structural features. These include the presence of a fully ossified skeleton and a swim bladder that holds the body in the water column. The respiratory organs of bony fish are protected by gill covers. The latter not only protect them, but also take part in the implementation of respiratory movements.

Fish without scales: is it possible

Numerous glands are located in the skin of fish. They perform a protective function. The substances released by them prevent the penetration of pathogens, reduce the friction of water during swimming. At certain types mucus contains toxic substances.

The body of bony fish is also covered with scales, which are derivatives of the skin. It looks like translucent flat plates. Separate scales are superimposed on each other like tiles. With its front edge, each plate goes deep into the skin, and the back one covers the scale of the next row. The growth of these structures is similar to the formation of growth rings in trees. The growth of the plates occurs in the spring, and stops in the winter.

Do all fish have scales? Absolutely. But in some it completely covers the body, while in others it is located on the body in separate rows. The latter is traditionally cartilaginous fish and some Bones. For example, in beluga, sterlet, sturgeon and stellate sturgeon, sharp scales are located along the body in several strands.

Cover features

All the features of the external structure of the fish allow them to better adapt to life in the aquatic environment. Not only the speed of movement, but also the color of the covers allows them to hide from predators. In many fish it is protective. For example, the dorsal side of a perch is darker than the ventral side. This makes the fish less visible against the bottom. The belly of the perch is silvery. This makes it invisible against the background of the surface of the water for prey, which is located below. The transverse stripes provide the perch with excellent camouflage among the thickets of algae.

In other species, the color is variegated and bright. It is called warning because its owners are almost always poisonous. Flounder has the ability to change its color depending on environmental conditions.

What is the lateral line in fish

On both sides of the body, a thin strip is clearly visible to the naked eye. It extends from the gill slits to the base of the tail. This structure is called the lateral line. It consists of receptors called neuromasts. The latter are formed by a group of hair cells.

The lateral line in fish is an organ of perception of vibrations and movements in environment. With its help, fish determine the direction and speed of the current. A similar structure was found in all larvae and some adult species of amphibians, cephalopods, and crustaceans. Fish use it as a guide in space, which is especially important when hunting.

unusual views

In spite of a large number of common features buildings, there are a number of aquatic life, which are in no way similar to representatives of this class. One of them is the drop fish. For most of her life, she has a normal appearance: a tail, scales, fins... However, when she rises to the surface of the water, her body begins to swell and turn into a gelatinous creature, similar to a monster with a huge nose.

Body fish can be found in coral ocean reefs. It has the shape of a cube. To that unusual way you can add a bright yellow color with black dots. So far, scientists cannot explain why, in the process of evolutionary changes, the classical flat shape of the body changed to a cubic one.

Flat head with a vermiform process, on which the eyes are located blue color, a huge mouth, bright stripes on the skin ... Such an organism really exists. It's called the frogfish. It was discovered in Indonesian waters not so long ago - in 2009.

And how not to say about the astrologer fish! You definitely won't confuse her with anyone. The stargazer is recognizable by its two bulging eyes and a wide mouth that sits on top of its head. It burrows into the sand, stalking its prey. At first glance, this is an absolutely harmless fish. In fact, its spikes, located above the dorsal fins, contain poisonous substances and are capable of generating a small amount of electric current.

So, the features of the external structure of fish that help them adapt to life in the water include:

• Streamlined body shape. It consists of a head, body and tail. In demersal species that lead a sedentary lifestyle, the body is flattened in the dorsal-abdominal direction.
• A large number of glands that secrete mucus.
• Scales that completely cover the body of fish or form longitudinal stripes.
• In cartilaginous fish, the respiratory organs open outwards through gill slits. In bone, they are closed with lids that protect the respiratory organs and are involved in the implementation of respiratory movements.
• The presence of several types of fins: paired and unpaired. The first group includes abdominal and thoracic. Dorsal, caudal and anal are unpaired. They provide all kinds of movements, maneuverability and a stable position in the water column.

Fish are the largest group of vertebrates. It includes about 30 thousand modern species. Fish are divided into two classes - Cartilaginous fish (sharks, rays) and bony fish(sturgeon, salmon, herring, crucian carp, perch, pike, etc.). The main criterion for such a division is the substance that makes up the internal skeleton of fish - cartilage or bone.

Fish inhabit various water bodies of our planet: oceans, seas, rivers, lakes, ponds. The aquatic environment is very extensive: the area occupied by the oceans exceeds 70% of the Earth's surface, and most deep depressions go deep into the oceans at 11 thousand meters.

The variety of living conditions in the water influenced the appearance of fish and led to the emergence of a wide variety of forms: the appearance of many adaptations to specific living conditions (Fig. 115).

Rice. 115. Fish of various ecological groups: 1,2 - living in the water column (pelagic) tuna and cod: 3 - surface flying fish; 4 - bottom flounder

In fish, the laterally compressed body has a streamlined shape. It has a head, body and tail.

Outside, the body of the fish is covered with skin, in which there are small (like perch) or large (like carp) bone scales. They tile-like overlap each other and tightly cover the body and tail. The scales are constantly growing, and annual rings are formed on it; they can be used to determine the age of the fish (Fig. 116, B, C). There are fish and bare-skinned, without scales (for example, catfish). The body of the fish is slippery, as it is covered with secretions of mucous glands located in the skin. The scales are painted in silver-gray, black tones. Many fish are characterized by bright colors, especially those that live among coral reefs.

Rice. 116. External structure fish: A - overall plan structures: 1 - nostril; 2 - eye; 3 - mouth; 4 - gill cover; 5 - pectoral fin; 6 - ventral fins; 7 - dorsal fin; 8 - anus; 9 - anal fin; 10 - lateral line; 11 - tail fin; B - scales with annual rings; B - determining the age of the fish

Fish have limbs - unpaired and paired fins. Unpaired are dorsal, caudal and anal, or caudal. The most important of them is the tail. It serves as the main motor organ - with its help, the fish move forward. Bottom on the sides are paired fins: front - pectoral, rear - abdominal. The pectorals are more mobile, they are involved in turning the body in the water, moving up, down and to the sides. The ventral and non-paired fins hold the body of the fish in a normal, upright position. Three openings are visible behind the ventral fins: anal, genital and urinary. Undigested food residues are ejected through the anal, harmful waste products are excreted through the urinary tract, reproductive products are excreted through the genitals: caviar in females and seminal fluid in males.

On the sides of the body of the fish are the organs of the lateral line - channels lying in the skin under the scales, at the bottom of which there are sensitive cells that perceive water vibrations. These organs allow the fish to perceive streams of water flowing around the body, to distinguish objects due to the waves that depart from these objects.

Other sense organs are located on the head. The border between the head and the body is considered the posterior edge of the gill covers (see Fig. 116, A). They cover their gills and constantly move, providing fresh water rich in oxygen to the gills. The border between the trunk and tail is conditionally drawn at the level of the anus.

A mouth is visible on the front of the head. The mouth of the fish captures food and draws in the water necessary for breathing. Above the mouth are nostrils that open into the organs of smell, with the help of which the fish perceives the smells of substances dissolved in water. The eyes of the fish are quite large. The anterior side of the outer shell (cornea) is flat. Below it is a convex lens (crystalline lens), which gives a reduced image of objects on the retina, cells that perceive light stimuli. The fish see close range and distinguish colors.

The hearing organs are not visible on the surface of the head: they are located on the sides of the head inside the skull. sound waves in water, the fish perceives the entire surface of the body. These vibrations cause irritation of the nerve endings of the inner ear, and the resulting excitations are transmitted along the auditory nerves to the brain. Near the inner ear is the organ of balance, thanks to which the fish feels the position of its body, moving up and down.

Lab #6

Topic. The external structure and features of the movement of fish.

Target. To study the external structure and methods of movement of fish.

Equipment: a jar of fish in water, a magnifying glass, a glass slide, fish scales.

Progress

1. Consider a fish in a jar of water. Explain the importance of her body shape.
2. Consider the coloration of the body of the fish on the ventral and dorsal sides. If it is different, then indicate the reasons for these differences.
3. How are the scales on the body of a fish? What significance does this have for the life of fish in the water? Using a magnifying glass, examine the structure of a separate scale.
4. Find the body parts of the fish: head, body, tail. Set their boundaries. Explain the importance of smooth transitions of body parts for the life of fish in water.
5. Find the nostrils, eyes, lateral line of the fish. What is the importance of these organs in the life of a fish? Find out what is the peculiarity of the structure of the eyes.
6. Examine the fins of the fish. Which of them are paired, which are unpaired. Watch how the fins work as the fish moves through the water.
7. Sketch the fish in question. Label the parts of the body in the drawing. Make a conclusion about the adaptability of fish to life in water. Draw a fish scale, marking the light and dark stripes. What is the age of the fish from which this scale was taken?

Fish are well adapted to life in the aquatic environment. They have a streamlined body shape, fins that provide movement in the water, sensory organs that allow them to navigate in the water.

Lesson learned exercises

1. In appearance, determine the habitats of the fish shown in Figure 115 (p. 10).
2. What is the structure of the integuments of the body of fish and what is their significance in the life of fish?
3. What sensory organs do fish use to navigate in the water?
4. Name the fins of a fish and describe their functions.