What fins help fish change the direction of movement. Fins perform different functions

To get food and escape from enemies, fish must move through dense water. Therefore, they all have a streamlined body shape, which makes it easier for them to overcome water resistance. There are no protrusions or transitions between the head, body and tail and there is no clear boundary. The wedge-shaped head, adapted to cut through water, is motionlessly articulated with the spine.

Fish that make long journeys or constantly live in rapid waters have the most perfect streamlined shape - their body is ridged or spindle-shaped and equipped with a powerful tail. Fish that live in calm waters have a tall body, adapted to quickly change direction of movement. They differ in the shape of the body of fish living on the bottom (they are, as it were, flattened) and in the upper layers of water (with flat sides).

The body shape is also influenced by the feeding pattern of fish. Predators forced to catch up with prey have a longer and more protruding body. Fish that eat sedentary food are shorter in length than predators, but significantly exceed their body height.

The main motor organ of fish is the tail, with the help of which they seem to push away from the water. Most of our fish have tails equipped with two-lobed fins; catfish, burbot and some others have a single-lobed tail fin.

In addition to the caudal fin, there are two pectoral fins, located near the head on both sides of the body, and behind them and slightly below - two abdominal fins. The unpaired subcaudal fin is located on the belly behind the anus. There are two (perch, pike perch) or one (pike) dorsal fins on the back.

Fins are formations consisting of hard and soft bone rays connected by membranes. The purpose of the tail is to help move forward.

The dorsal and subcaudal keels are a kind of keels that regulate the position of the fish’s body in the vertical plane. The pectoral and pelvic fins make it easier for the fish to move up and down and during turns.

On the outside, the entire body of the fish is covered with a thin flexible shell formed by bony plates - scales. There are three types of scales. In carp (white) fish, they have a rounded leading edge; Such scales do not sit firmly in the skin and fall off easily.

Perches have serrated scales; They sit very firmly in the skin. The body of sturgeons is covered with scales with a tooth protruding in the middle.

The size of the scales increases as the fish grows. But this happens not due to the expansion of the existing plate, but due to the appearance of a new, larger, young scale underneath it. In other words, as the age of the fish increases, the scales increase in both width and thickness. It becomes like a stack of thin plates superimposed on each other and fused together, of which the top one is the oldest and smallest, and the bottom one is the largest and youngest. This feature of scale growth allowed scientists to develop a method for determining the age of fish.

The scales taken above the lateral line under the dorsal fin are thoroughly cleaned of any remaining skin and mucus and placed under a magnifying glass of 8-10x magnification. The concentric rings visible through a magnifying glass are the edges of all the gradually formed plates.

But the growth of fish, and therefore the growth of scales, is uneven throughout the year. In summer, the fish actively feed and grow faster, so the distances between the edges of the plates are the widest. In autumn, due to the slowdown in fish growth, they narrow. And in winter they get so close that they form one dark ring. The following summer, new wide concentric rings appear on the plate, tapering in autumn and winter. Therefore, the number of dark rings on the fish’s scales will correspond to the number of years of its life.

In addition to the scaly shell, the body of the fish is also covered with an abundant layer of mucus. She performs a dual role. Firstly, it protects the skin from fungi, bacteria, mechanical suspensions in water and the effects of various chemical salts. And, secondly, like any lubricant, it makes it easier for the fish to glide in the water.

A hydrostatic apparatus such as a swim bladder also helps fish move faster through the water column with little expenditure of muscle energy. It is located in the body cavity under the spine and communicates in some fish with the pharyngeal cavity, in others with the anus. In order to go to depth, the fish releases part of the gas located there from the bubble.

Many people think that fish swim using fins. After all, the word “fin” itself means an organ that carries out swimming, a mover in a liquid environment.

Even some textbooks say that the fish swims by performing rowing movements with its tail fin, that is, bringing it forward and then straightening it with force.

This explanation of the mechanism of fish swimming is completely incorrect. After all, when moving the caudal fin to the side for the next “stroke”, the fish will push back approximately the same amount as it will then move forward when the tail is straightened. “Rowing movements” would mean continuous fidgeting, slipping in one place.

Let's try to completely cut off the tail fin; it turns out that the fish retains the ability to swim forward at the same speed. In addition, many fish do not have a caudal fin at all in the usual sense of the word: the body ends in a rope-like thread, which cannot in any way be used for rowing movements.

Nevertheless, these fish swim quite quickly. But if you squeeze the fish’s body between two thin strips tied with thread, i.e., as if enclosing the fish in splints, leaving the caudal fin completely free, then the fish will be incapable of forward movement. To swim forward, the fish must bend its body in a wave-like manner, just as a swimming snake does, for example.

A continuous wave running from head to tail is the main mechanism of movement of both the snake and the fish. Only in snakes the wave-like bends come from the very front end of the body, and in most fish - from approximately the middle. However, some fish with a serpentine body, such as eels, perform exactly the same swimming movements as snakes. A similar swimming pattern is characteristic of both the lamprey and the leech - only in the latter the body bends not to the sides, but up and down.

What is the role of the caudal fin? After its removal, the movement of the fish does not slow down, but becomes somewhat uneven; the fish seems to be “prowling.” Consequently, the caudal fin helps to gently “throw off” the waves running through the fish’s body and evens out the forward movement.

During sharp turns of a fast-swimming fish, the tail acts as a rudder: the fish moves it in the direction in which it turns. The fastest swimmers, such as tuna and swordfish, have a caudal fin in the form of a narrow crescent, with very long blades that diverge almost vertically up and down.

When a fish swims quickly, a vortex zone forms behind it; however, tuna and swordfish have the tips of their tail blades outside this zone, facilitating precise turns.
The speed of movement of many fish is amazing. The London Museum houses part of a ship's bottom, pierced through with a swordfish. Her weapon - a sword - passed through the copper plating of the ship's hull, an oak frame 30 cm thick and broke off. The famous mathematician A. N. Krylov calculated that such a breaking force is possible at a speed of about 90 km/h.

According to modern data, swordfish can reach speeds of up to 130 km/h. A bone outgrowth - the sword serves her not so much as a weapon, but as a device for cutting water, a kind of “stem”. Sometimes there are specimens that have broken off their sword, but successfully obtain food; therefore, this weapon is not so necessary to defeat the victim.

Tuna can reach speeds of about 90 km/h, some sharks and salmon - up to 45 km/h, carp - 12 km/h. In all cases, we are talking about moving over a short distance, so to speak, at a “sprint” distance.

It is remarkable that the fastest fish swim at about the same speed as the fastest birds fly, even though water is much denser than air.
Man is only three to four times slower in running speed than the fastest-footed land animals, and swims about twenty times slower than the fastest fish.
It is also interesting that modern airplanes and cars are much faster than birds and four-legged animals, but so far not a single underwater vessel can outrun the swordfish.

Forward movement is not the only way of movement in the world of fish. Stingrays, for example, move forward thanks to the wave-like vibrations of their pectoral fins-wings. In some freshwater fish, the propulsion wave runs along a very long dorsal fin, not necessarily from head to tail, but sometimes in the opposite direction, then the fish slowly swims “backward,” i.e., tail first.

The beautiful Black Sea fish greenfinch can swim slowly, making rowing movements with its pectoral fins, either alternately or with both of them together. The pectoral fins also help the fish maintain a normal position (back up). After all, the ventral side of the fish, where the body cavity is located, is much lighter than the fleshy dorsal side. In other words, the fish's center of gravity lies above its center of buoyancy; the fish is always in an unstable equilibrium, and when dead or stunned, it turns over with its belly up.

A fish floating motionless in the water maintains a normal body position with continuous movements of the pectoral fins. However, fish are also known that constantly swim with their belly up; some always maintain a vertical position (“candle”), for example, sea pike (paralepis), seahorse.

The fish uses its pectoral fins as depth rudders, turning up or down while moving. A stationary fish turns up or down with the help of unpaired fins, such as the anal fin (located on the underside of the body between the anus and the tail). Working with the anal fin, the fish creates a force that rotates the body around a horizontal transverse axis, tilting the head down.

The fish performs this movement, for example, when capturing food from the bottom. It is no coincidence that many fish that feed primarily on bottom animals have a very large anal fin. And when grabbing prey located above the mouth, for example on the surface of the water, the fish uses its dorsal fin if it is located far behind the middle of the body. Such a fin creates a torque, turning the fish around a horizontal axis, raising the head part of the body and lowering the tail part.

In many fish, the dorsal fin is located in the middle of the body, and the ventral fins are located directly below it. Such fish, turning sharply to the side while swimming, raise their dorsal fin and spread their ventral fins; thereby creating additional resistance to movement and extinguishing inertia. This is how a running person makes it easier for himself to quickly turn by grabbing onto some stationary object, such as a tree.

In some fish, such as cod, the pelvic fins sit in front of the pectoral fins and play the role of additional depth rudders. There are fish that, along with swimming, use completely different methods of movement.

Flying fish are often found in tropical seas. Having developed great speed, they straighten their huge pectoral fins, lift off from the surface of the water and can glide for over 15 seconds, as if on wings, covering a distance of more than 100 m. The elongated lower blade of the caudal fin helps the flying fish regulate speed and direction just before the moment of takeoff: already when the body came out of the water, the tail blade was still submerged. Emerging from the water, flying fish escape from predatory fish (tuna, golden mackerel, etc.).

Using a suction cup located on the head, the sticky fish attaches itself to sharks, whales, and turtles and is transported by them over long distances. Popular books often describe how the natives catch turtles with the help of a sticky fish: released into the sea on a leash, it is firmly attached to the shell of the turtle, which can only be pulled into the boat.

The Caspian lamprey attaches itself to salmon and travels up the river to its spawning grounds. The creeper fish crawls ashore at night, resting its pectoral fins on the ground, and searches for food, such as earthworms. Another amazing fish - the mudskipper, during low tide, climbs onto inclined roots and tree trunks, and moves along the ground in leaps, leaning on its belly and pectoral fins.

Their coloring is very closely related to the nature of movement and in general to the way of life of fish. For example, herring has a dark back and, when viewed from above, blends in with the blue depths of the sea. The silvery sides and belly make the herring almost indistinguishable from below, against the background of the sparkling surface of the sea. The spotted coloring of pike is a means of camouflage in underwater thickets, where the predator usually hides, lying in wait for prey.

Bottom-dwelling fish, such as flounder, are strikingly similar in color to the substrate. Swimming from a dark, muddy bottom to a light, sandy bottom, the flounder quickly becomes lighter in color. Coloring is regulated by vision. If you place a flounder so that its entire body lies on a dark bottom and its head on a light one, the fish acquires a light color.

Every amateur fisherman knows that river perch caught in a clean stream with a sandy bottom is always much lighter than its counterpart from a deep muddy pool shaded by trees. Sea bass, freshly raised from great depths, has a bright scarlet color; After lying on the deck in daylight, it gradually becomes ash-gray, and when put away in the dark hold, it turns red again.

A fish with a black cover placed over its eyes, and also completely blinded, soon acquires a dark color. Tropical fish, living in the brightly lit sea among coral reefs, sparkle with variegated colors. Striped, spotted and blue catfish are common in the northern seas. Striped is most often found near the coast, among underwater vegetation; spotted - on muddy, rocky or shell bottoms; The blue one floats in the water for a long time. As we can see, in these cases, the color of the fish matches its habitat well.

However, the coloring of some fish is striking from a distance. For example, the back of the electric stingray is dotted with bright spots. In all likelihood they act as warning signs; after all, any predator that attacks an electric stingray receives a proper rebuff. Warning coloration is quite common among terrestrial animals that have some effective means of defense - just remember the wasp with its poisonous sting and black and yellow, visible from afar outfit.

On the silver side of the haddock, a large black spot catches the eye. There is reason to think that it plays the role of an identification mark, helping fish of the same school to move together. As a rule, haddock stays in shallow areas with sandy or shell soil, where there is enough light to see their schoolmates.

Some fish that live in the water at great depths, such as the glowing anchovy, are covered with spots that emit a bluish glow. In the Gulf of Mexico there is a fish in which luminous points lie in an even line along the ventral side of the body, somewhat reminiscent of a row of buttons on a jacket. This fish was nicknamed “sea midshipman”. The number and location of luminous spots are very characteristic of each species - they help fish keep track of their schoolmates and find each other during the breeding season.

The scaly cover of many fish shines brightly. Bleak scales are even used to make pearl pasta, which is used to cover glass balls, turning them into artificial pearls. But the main coloring features of the fish still depend not on the scales, which are generally quite transparent, but on the coloring matter - the pigment found in the skin. Some pigment cells give the skin a yellow color, others - red, others - black, etc. Under the influence of visual perceptions, the central nervous system of fish sends signals to the skin that cause certain pigment cells to shrink or expand, as a result of which the color of the fish changes.

It is usually believed that the scaly cover, like a shell, “protects the fish from enemies.” But this is completely false, because almost all fish-eating predators - for example, a heron or a pelican, a seal or a dolphin, a pike or a shark - swallow their prey whole. For those that eat fish in parts (for example, a river otter), scales are not a hindrance.

The role of the scaly cover is completely different: it gives the fish’s body the firmness and elasticity necessary for effective swimming movements. The strongest and fastest swimmers (tuna, swordfish) even have special “keels” on the caudal peduncle, something like rigid hinges capable of making a clear translational movement. Fish with an elongated, serpentine body, swimming relatively slowly, have very small scales or are completely absent; These are eel, burbot, loach, catfish, catfish, gerbil, butterfish, and lumpenus.

If scales have a protective value, then why are they absent (or very poorly developed) in all of the listed fish? The least developed scale cover is on the ventral side of the body, although the vital organs located there would seem to be in particular need of protection. In a developing fry, scales first appear in the caudal part of the body, which is understandable, since it is the caudal fin that serves as the “propulsion” of the fish.

The number of scales on the body of a fish almost does not change with age and is characteristic of each species. When describing fish in textbooks, guides and atlases, the number of scales in the lateral line is usually indicated. After the migration of Far Eastern pink salmon to the European north, local fishermen sometimes mixed them with young salmon. These fish are indeed similar, however, pink salmon have at least 140 scales in the lateral line, and salmon - no more than 130.

Laboratory work

Fins and types of fish movement

Purpose of the lesson

Consider the shapes, types, location and structure of fish fins using the example of sturgeon (Russian sturgeon, beluga) and bony fish (river perch, crucian carp, bream, flounder, etc.)

Material and equipment

Frozen fish: Russian sturgeon, silver crucian carp, river perch; sea ​​flounder, bream, etc.; fixed material of sturgeon and bony fish, dummies, posters and drawings; metal cuvettes, tweezers, scalpels, dissecting needles and scissors, calculator (computer).

General position

Fins. Their sizes, shape, quantity, position and functions are different. The fins allow the body to maintain balance and participate in movement.

Rice. 1 Fins

The fins are divided into paired, corresponding to the limbs of higher vertebrates, and unpaired (Fig. 1).

TO doubles relate:

1) chest P ( pinna pectoralis);

2) abdominal V. ( R. ventralis).

TO unpaired:

1) dorsal D ( p. dorsalis);

2) anal A (R. analis);

3) tail C ( R. caudalis).

4) fat ar (( p.adiposa).

In salmonids, characins, killer whales, and others, there is a adipose fin(Fig. 2), devoid of fin rays ( p.adiposa).

Rice. 2 Adipose fin

Pectoral fins common in bony fishes. In stingrays, the pectoral fins are enlarged and are the main organs of movement.

Pelvic fins occupy different positions in fish, which is associated with a movement of the center of gravity caused by contraction of the abdominal cavity and concentration of viscera in the front part of the body.

Abdominal position– pelvic fins are located in the middle of the abdomen (sharks, herring, carp) (Fig. 3).

Rice. 3 Abdominal position

Thoracic position– the pelvic fins are shifted to the front of the body (perciform) (Fig. 4).

Rice. 4 Thoracic position

Jugular position– the pelvic fins are located in front of the pectoral fins and on the throat (cod fins) (Fig. 5).

Rice. 5 Jugular position

Dorsal fins there may be one (herring-like, carp-like), two (mullet-like, perch-like) or three (cod-like). Their location is different. In pike, the dorsal fin is shifted back, in herrings and cyprinids it is located in the middle of the body, in fish with a massive front part of the body (perch, cod) one of them is located closer to the head.

Anal fin Usually there is one, cod has two, and the spiny shark does not have one.

Caudal fin has a varied structure.

Depending on the size of the upper and lower blades, they are distinguished:

1)isobathic type – in the fin the upper and lower blades are the same (tuna, mackerel);

Rice. 6 Isobath type

2)hypobate type – the lower blade is lengthened (flying fish);

Rice. 7 Hypobate type

3)epibate type – the upper blade is lengthened (sharks, sturgeon).

Rice. 8. Epibathic type

Based on their shape and location relative to the end of the spine, several types are distinguished:

1) Protocercal type - in the form of a fin border (lamprey) (Fig. 9).

Rice. 9 Protocercal type -

2) Heterocercal type – asymmetrical, when the end of the spine enters the upper, most elongated blade of the fin (sharks, sturgeon) (Fig. 10).

Rice. 10 Heterocercal type;

3) Homocercal type – externally symmetrical, with the modified body of the last vertebra extending into the upper lobe (bony) (

Rice. 11 Homocercal type

The fins are supported by fin rays. In fish, branched and unbranched rays are distinguished (Fig. 12).

Unbranched fin rays can be:

1)articulated (capable of bending);

2)inarticulate hard (spiny), which in turn are smooth and jagged.

Rice. 12 Types of fin rays

The number of rays in the fins, especially in the dorsal and anal, is a species characteristic.

The number of spiny rays is indicated by Roman numerals, and the branched rays - by Arabic numerals. For example, the dorsal fin formula for river perch is:

DXIII-XVII, I-III 12-16.

This means that the perch has two dorsal fins, the first of which consists of 13 - 17 spiny fins, the second of 2 - 3 spiny and 12-16 branched rays.

Functions of fins

· Caudal fin creates a driving force, ensures high maneuverability of the fish when turning, and acts as a rudder.

· Thoracic and abdominal (paired fins ) maintain balance and act as rudders when turning and at depth.

· Dorsal and anal the fins act as a keel, preventing the body from rotating around its axis.

Fish movement methods

The variety of living conditions of fish also determines their methods of movement. Fish have three known modes of locomotion: swimming, crawling and flying .

Swimming - the main type of movement, which is carried out mainly due to the lateral bends of the body and tail.

Distinguish two types of swimming using lateral bends of the body:

Mackerel– in fish when swimming, the tail is of great importance, with the help of which the fish pushes off from the water and moves forward, which accounts for about 40% of the total driving force (mackerel, salmon).

Acne-shaped (serpentine)– in fish, when moving, the whole body bends in a wave-like manner. This is the most economical type of movement; the swimming speed is low (lamprey, eel, loach).

Fish swim at different speeds. The fastest is swordfish, capable of reaching speeds of up to 33 m/s (118.8 km/h), tuna swims at speeds of up to 20 m/s (72 km/h), salmon - 5 m/s (18 km/h). hour).

The speed of movement of fish is also dependent on body length. In accordance with this, it is determined speed coefficient - the ratio of absolute speed to the square root of its length:

Based on the speed of movement, the following groups of fish are distinguished:

1) very fast (swordfish, tuna) - speed coefficient about 70;

2) fast ones (salmon, mackerel) – 30–60;

3) moderately fast (mullet, cod, herring) – 20–30;

4) slow ones (carp, bream) – 10–20;

5) slow (gobies) – 5–10;

6) very slow (stickleback, sunfish) – 5.

Fish of the same species can swim at different speeds. There are:

1. Throwing speed(speed factor 30–70), which

develops within a very short time (during fright, rushing at prey).

2. Cruising speed(speed factor 1–4) with which fish swim for a long time.

Crawl on the ground is one of the ways fish move, which is carried out mainly with the help of pectoral fins and tail (creeper, monkfish, multifin, jumper, gurnard). Thus, the jumper lives in mangroves and spends a significant part of its time on the shore. It moves on land by jumping, which it makes with the help of its tail and pectoral fins, and feeds on terrestrial invertebrates.

Flight(air soaring) characteristic of a few flying fish that live in the pelagic zone of tropical and subtropical waters of the World Ocean. These fish have long and wide pectoral fins that serve as wings. The tail with a highly developed lower blade is the engine that gives the initial speed. Having jumped out to the surface of the water, the flying fish first glides along the water surface, and with increasing speed of movement it breaks away from the water, flying a distance of up to 200 and even 400 m.

Progress

1. Familiarize yourself with the content of the theoretical material presented in the guidelines.

2. Consider the shapes, types, location and structure of fins of fish prepared for laboratory work. Draw a schematic diagram of a salmon and highlight paired and unpaired fins on the diagram. Name the functions of different fins.

3. List the different positions of the pelvic fins and give examples.

4. List and sketch the types of caudal fins by structure and by shape and location relative to the end of the spine.

5. Consider the structure of the dorsal fins of the perch, highlight the unbranched (spiny) and branched (jointed) rays. Write down the formula for the dorsal fin of a perch and the dorsal and anal fins of a goldfish or other fish of your choice.

6. Give examples of fish with different types of swimming.

7. Using a computer calculator, determine the speed coefficient - the ratio of the absolute speed to the square root of its length. If necessary, change the speed to km/h.

for swordfish,(V = 33 m/s, L= 170 cm),

tuna(V = 20 m/s, L= 120 cm 20 m/s),

salmon– (V = 33 m/s, L= 70 cm).

Control questions:

1. Functions of fish fins

2. Shapes, types, location and structure of fish fins

3. Methods of movement of fish.

4. Define cruising and throwing speeds, give examples.

5. How is the fish speed coefficient calculated?

Vasilyeva E.D., Luzhnyak V.A. Fishes of the Azov Sea basin [ch. ed. acad. G.G. Matishov]. – Rostov n/d: Publishing house of the Southern Scientific Center of the Russian Academy of Sciences, 2013. – 272 p.

Ivanov V.P., Egorova V.I. Fundamentals of ichthyology: textbook. allowance. Astrakhan. state tech. univ. – 2nd ed., additional. and clarification – Astrakhan: ASTU Publishing House, 2008. – 336 p.

Ivanov V.P., Komarova G.V. Fishes of the Caspian Sea (systematics, biology, fishing). Astrakhan State Technical University – 2nd ed., additional and clarification – Astrakhan: ASTU Publishing House, 2012. – 256 p.

Ilmast N.V. Introduction to ichthyology (textbook). – Petrozavodsk: Karelian Scientific Center of the Russian Academy of Sciences. 2005. 148 p.

Kotlyar O.A., Mamontova R.P., Course of lectures on ichthyology. – M.: Kolos, 2007.

Moiseev P.A., Azizova N.A., Kuranova I.I. Ichthyology: Textbook.-M.: Easy. and food industry, 1981.- 384 p.

Skornyakov V.I., Apollova T.A., Mukhordova L.L. Workshop on ichthyology: Textbook - M.: Agropromidat, 1986. - 270 p.

Compiled by:

STARTSEV Alexander Veniaminovich

STARTSEVA Marina Leontievna

Fins and types of fish movement

Guidelines for laboratory work

in the discipline "Ichthyology"

Publishing center DSTU

Address of the university and printing enterprise:

344000, Rostov-on-Don, pl. Gagarina, 1

Fish - aquatic animals, adapted to life in fresh water and sea water. They have a hard skeleton (bone, cartilaginous or partially ossified).

Let us consider the structural features and vital functions of fish using the example of river perch.

Habitat and external structure of fish using the example of river perch

River perch lives in freshwater bodies of water (slow-flowing rivers and lakes) in Europe, Siberia and Central Asia. Water exhibits noticeable resistance to bodies moving in it. Perch, like many other fish, has a streamlined shape - this helps it move quickly in the water. The perch's head smoothly transitions into the body, and the body into the tail. At the pointed front end of the head there is a mouth with lips that can open wide.

Figure: external structure of river perch

On the top of the head two pairs of small holes are visible - nostrils leading to the olfactory organ. On its sides there are two large eyes.

Perch fins

Bending the laterally flattened body and tail first to the right and then to the left, the perch moves forward. When swimming, fins play an important role. Each fin consists of a thin membrane of skin, which is supported by bony fin rays. When the rays spread out, the skin between them tightens and the surface of the fin increases. On the back of the perch there are two fin pins: front big And the rear one is smaller. The number of dorsal fins may vary between different fish species. At the end of the tail there is a large two-lobed caudal fin, on the underside of the tail - anal. All these fins are unpaired. Fish also have paired fins - there are always two pairs of them. Pectoral fins(front pair of limbs) are placed on the sides of the perch’s body behind the head, paired pelvic fins (back pair of limbs) are on the underside of the body. The main role in moving forward is played by caudal fin. The paired fins are important for turning, stopping, moving forward slowly, and maintaining balance.

The dorsal and anal fins give the fish body stability when moving forward and making sharp turns.

Cover and color of perch

The body of the perch is covered bone scales. Each scale with its front edge is immersed in the skin, and with its rear edge it overlaps the scales of the next row. Together they form a protective cover - scales that does not interfere with body movements. As the fish grows, the scales also increase in size and can be used to determine the age of the fish.

The outside of the scales is covered with a layer of mucus, which is secreted by the skin glands. Mucus reduces friction between the fish's body and water and serves as protection against bacteria and mold.

Like most fish, the belly of the perch is lighter than the back. From above, the back to a certain extent merges with the dark background of the bottom. From below, the light belly is less noticeable against the light background of the water surface.

The body color of a perch depends on the environment. In forest lakes with a dark bottom it has a dark color, sometimes even completely black perches are found there. Perches with light and bright colors live in reservoirs with a light sandy bottom. Perch often hides in thickets. Here the greenish color of its sides with vertical dark stripes makes the perch invisible. This protective coloring helps him hide from enemies and better watch over his prey.

Along the sides of the perch's body from head to tail runs a narrow dark lateral line. This is a kind of sensory organ.

The skeleton of a perch consists of a large number of bones. Its basis is the spine, which stretches along the entire body of the fish from the head to the caudal fin. The spine is formed by a large number of vertebrae (perch has 39-42).

Figure: Skeleton of a river perch

When a perch develops in the egg, a notochord appears in the place of its future spine. Later, vertebrae appear around the notochord. In adult perch, only small cartilaginous remains between the vertebrae are preserved from the notochord.

Each vertebra consists of body And upper arch, ending in a long upper process. Taken together, the upper arches together with the vertebral bodies form the spinal canal, which contains spinal cord.

In the trunk section of the body, they are attached to the vertebrae at the sides ribs. There are no ribs in the caudal region; each vertebra located in it is equipped with a lower arch ending in a long lower process.

In front, the skeleton of the head is firmly articulated with the spine - scull. There is also a skeleton in the fins.

In paired pectoral fins, the skeleton of the fins is connected to the spine by bones shoulder girdle. The bones connecting the skeleton of the paired pelvic fins to the spine are not developed in the perch.

The skeleton is of great importance: it serves as a support for muscles and protection for internal organs.

River perch muscles

Under the skin there are muscles attached to the bones that form muscles. The strongest of them are located on the dorsal side of the body and in the tail.

The contraction and relaxation of muscles causes the fish's body to bend, allowing it to move in the water. The head and fins contain muscles that move the jaws, gill covers and fins.

Swim bladder of river perch

River perch, like any fish, is heavier than water. Its buoyancy ensures swim bladder. It is located in the abdominal cavity above the intestines and has the shape of a translucent sac filled with gas.

Figure: Internal structure of river perch. Digestive and excretory systems

The swim bladder is formed in the perch embryo as an outgrowth of the intestine on the dorsal side. It loses connection with the gut during the larval stage. On the 2-3rd day after hatching, the larva should float to the surface of the water and swallow some atmospheric air to fill the swim bladder. If this does not happen, the larva cannot swim and dies.
By regulating the volume of the swim bladder, the perch stays at a certain depth, floats up or sinks. When the bladder contracts, excess gas is absorbed by the blood in the capillaries of the inner surface of the bladder. If the bubble expands, gas enters it from the blood. When the perch sinks into the depths, the bubble decreases in volume - and the density of the fish increases. This promotes rapid immersion. When floating, the volume of the bubble increases and the fish becomes relatively lighter. At the same depth, the volume of the fish's bladder does not change. This allows the fish to remain motionless, as if hanging in the water column.
Unlike river perch, in other fish, such as carp, bream, roach, herring, the swim bladder remains connected to the intestine using an air duct - a thin tube throughout life. Excess gas exits through this duct into the intestines, and from there through the mouth and gill slits into the water.
The main function of the swim bladder is to provide buoyancy for fish. In addition, it helps fish hear better, since, being a good resonator, it amplifies sounds.

1. Tail fin creates a driving force, ensures high maneuverability of the fish when turning, and acts as a rudder.

2. Paired fins ( chest, abdominal) maintain balance and act as rudders when turning and at depth.

3. Dorsal and anal the fins act as a keel, preventing the body from rotating around its axis.

Yu. G. Aleev (1963) distinguishes four functional zones of fins in fish:

1st zone- front rudders and load-bearing planes; it includes the pectoral and pelvic fins (if they are located under the pectoral fins or in front of them);

2nd zone- keels; this includes the dorsal fin, located in front of the center of gravity, as well as the ventral fins, if they are located in front of the center of gravity; if there is only one dorsal fin (as in herrings and cyprinids), the front part of it enters this zone, if there are several of them, then the first part;

3rd zone- stabilizers, the role of which is played by the dorsal fin, located behind the center of gravity, and the anterior part of the anal fin, as well as the adipose fin (if present); in cod, for example, this zone includes the second dorsal and first anal, in salmon - the adipose and anal fins;

4th zone- rear steering wheels and locomotor organ; it includes the caudal fin and, in most fish, the posterior part of the dorsal and anal fins; in cod, this zone includes the third dorsal and second anal fins; This zone includes additional fins, which some fish have behind the dorsal and anal fins (mackerel) (Fig. 6).

Rice. 5. Functional zones of the fins and their position during straight-line movement (A) and when turning (B)(according to Aleev):

salmon; 2 - bonito; 3 - cod.

When moving in a straight line, the fins I and II zones in most fish do not function and are pressed to the body (the numbers in brackets indicate that the function of this zone for this fin is not the main one).

Ways of movement. The variety of living conditions of fish also determines their methods of movement. Fish have three known modes of locomotion: swimming, crawling and flying.

Swimming- the main type of movement, which is carried out mainly due to the lateral bends of the body and tail. The body of fish with a larger number of vertebrae bends more strongly. The short body of the fish moon (only 17 vertebrae) cannot bend. Fish, whose body structure excludes the possibility of lateral bends, swim using wave-like movements of the fins: electric eel - anal; moon fish and body - tail; pectoral slopes.

Distinguish two types of swimming using side bends

1. mackerel-shaped – in fish when swimming, the tail is of great importance, with the help of which the fish pushes off from the water and moves forward, which accounts for about 40% of the total driving force (mackerel, salmon).

2acne-shaped (serpentine) – in fish, when moving, the whole body bends in a wave-like manner. This is the most economical type of movement; the swimming speed is low (lamprey, eel, loach).

Rice. 5. Types of swimming a) mackerel-like, c) eel-like

Rice. 7. Movement of fish using wave-like movements of fins (according to Aleev):

1 - moon fish; 2- body; 3 - electric eel; 4 - flounder.

Those fish whose body structure excludes the possibility of lateral bends (cowfish, bluehorn, pipit, pipefish, moonfish, electric fish) swim using wave-like (undulating) movements of the vertebrae: electric eel; moon fish and body - tail; stingrays - pectorals

There are two types of swimming using lateral bends

Fish swim at different speeds. The fastest is swordfish, capable of reaching speeds of up to 33 m/s, tuna swims at speeds of up to 20 m/s, salmon - 5 m/s.

The speed of movement of fish is also in a certain dependence on the length of the body; in accordance with this, the speed coefficient is determined (the ratio of the absolute speed to the square root of its length ( V/√L).

Based on the speed of movement, the following groups of fish are distinguished:

1) very fast (swordfish, tuna) - speed coefficient about 70;

2) fast ones (salmon, mackerel) – 30–60;

3) moderately fast (mullet, cod, herring) – 20–30;

4) slow ones (carp, bream) – 10–20;

5) slow (gobies) – 5–10;

6) very chalked (stickleback, sunfish) – 5.

Fish of the same species can swim at different speeds. There are:

1. Throwing speed(speed factor 30–70), which

develops within a very short time (during fright, rushing at prey).

2. Cruising speed(speed factor 1–4) with which fish swim for a long time.

The speed of movement of fish depends on the structural features (body shape, scale cover, presence of mucus), physiological state, water temperature and other factors. Slow-swimming fish are characterized by a high body and large scales (cyprinids), as well as eel-like, ribbon-like, spherical body shapes. Fast-swimming fish have a well-streamlined body shape, small scales, a thin muscular caudal peduncle often with lateral keels (swordfish, tuna), a highly developed, almost symmetrical high caudal fin, additional fins behind the dorsal and anal fins (tuna, mackerel bonito). Many fast-swimming fish have peculiar fairings: fatty eyelids (mullet), elongated scales on the tail (blackback herring), etc.

Fishes swim in a horizontal position, however, differences are observed in some species. The seahorse moves upward in a helical line, using its dorsal and pectoral fins and bending its caudal peduncle, which lacks a caudal fin, in a wave-like manner. The crooktail, when gathering in schools, swims in a vertical position. Cirrus catfish from African rivers swim slowly at the surface of the water with their belly up. Special forms of swimming include passive movement of fish (sticky fish).

Crawl on the ground is one of the ways fish move, which is carried out mainly with the help of pectoral fins and tail (creeper, monkfish, multifin, jumper, gurnard). Thus, the jumper lives in mangroves and spends a significant part of its time on the shore. It moves on land by jumping, which it makes with the help of its tail and pectoral fins, and feeds on terrestrial invertebrates.

Flight (air soaring) characteristic of a few flying fish that live in the pelagic zone of tropical and subtropical waters of the World Ocean. These fish have long and wide pectoral fins that serve as wings. The tail with a highly developed lower blade is the engine that gives the initial speed. Having jumped to the surface of the water, the flying fish first glides along the water surface, and with increasing speed it breaks away from the water, flying a distance of up to 200 and even 400 m.