Many people think that fish swim with their fins. After all, the very word "fin" means an organ that carries out swimming, a mover in a liquid medium.
Even in some textbooks it is said that the fish swims, performing rowing movements with the tail fin, that is, bringing it forward, and then straightening it with force.
This explanation of the swimming mechanism of fish is completely wrong. After all, taking the tail fin to the side for the next “stroke”, the fish will push back about the same as it then moves 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 cord-like thread, which in no way can be used for rowing movements.
However, these fish swim quite fast. But if you squeeze the body of the fish between two thin planks tied with a thread, that is, as if enclosing the fish in splints, leaving the caudal fin completely free, then the fish will be incapable of forward movement. In order to swim forward, the fish must undulate its body, just as, for example, a swimming snake does.
A continuous wave running from head to tail is the main mechanism of movement for both snake and fish. Only in snakes, wave-like bends go from the very front end of the body, and in most fish - approximately from the middle. However, some fish with a serpentine body, such as eels, perform exactly the same swimming movements as snakes. A similar nature of swimming is characteristic of both the lamprey and the leech - only in the latter the body does not bend to the sides, but up and down.
What is the role of the tail 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 "drop" the waves running through the body of the fish, and evens out the forward movement.
During sharp turns of a fast-swimming fish, the tail acts like a rudder: the fish takes it in the direction in which it turns. The fastest swimmers, such as tuna, swordfish, have a tail fin in the form of a narrow crescent, with very long blades, diverging almost vertically up and down.
When a fish swims fast, a swirl zone forms behind it; however, in tuna and swordfish, the tips of the tail blades are outside this zone, which facilitates sharp turns.
The speed of movement of many fish is amazing. The London Museum has a part of the ship's bottom, pierced through by a swordfish. Her weapon - a sword - went through the copper sheathing of the ship's hull, an oak frame 30 cm thick and broke off. The famous mathematician A. N. Krylov calculated that such a penetrating 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. 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 broke off their sword, but successfully get food; therefore, this weapon is not so necessary for overcoming the victim.
Tunas 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 at a short distance, so to speak, at a “sprint” distance.
Remarkably, the fastest fish swim at about the same speed as the fastest birds, even though water is much denser than air.
Man is only three to four times slower than the fastest land animals, and swims about twenty times slower than the fastest fish.
It is also interesting that modern aircraft and cars have far surpassed birds and quadrupeds in speed, but not a single underwater vessel can overtake swordfish.
Translational motion is not the only way of movement in the world of fish. Stingrays, for example, move forward due to the wave-like vibrations of the pectoral fins-wings. In some freshwater fish, the motor wave runs along a very long dorsal fin, and not necessarily from head to tail, but sometimes in the opposite direction, then the fish slowly swims “reversely”, that is, tail first.
The beautiful Black Sea greenfinch fish can swim slowly, making rowing movements with its pectoral fins either alternately or both together. The pectoral fins also help the fish to 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. In other words, the center of gravity of the fish lies above the center of buoyancy; the fish is always in an unstable balance, and the dead or stunned fish turns belly up.
A fish floating motionlessly in the water maintains a normal body position with continuous movements of the pectoral fins. However, fish are also known that constantly swim upside down; some all the time maintain a vertical position (“candle”), for example, a sea pike (paralepis), a 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 anal (located on the underside of the body between the anus and tail). Working with the anal fin, the fish creates an effort that turns the body around a horizontal transverse axis, with the head tilted down.
The fish performs such a movement, for example, when capturing food from the bottom. It is no coincidence that many fish that feed mainly on bottom animals have a very large anal fin. And grabbing prey located above the mouth, for example, on the surface of the water, the fish works with the dorsal fin if it is located far behind the middle of the body. Such a fin creates a rotational moment, turning the fish around a horizontal axis, with the head part of the body rising and the tail part lowering.
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 during swimming, raise the dorsal fin and spread the abdominal ones; this creates additional resistance to movement and dampens inertia. So a running person facilitates a quick turn by grabbing some immovable object, such as a tree.
In some fish, such as codfish, the ventral fins sit in front of the pectoral fins and act as additional depth rudders. There are fish that, along with swimming, use completely different methods of transportation.
Flying fish are often found in tropical seas. Having developed great speed, they straighten their huge pectoral fins, break away from the surface of the water and can glide for more than 15 seconds, as if on wings, covering a distance of more than 100 m. the body is out of the water, the tail blade is still submerged. Emerging from the water, flying fish escape from predatory fish (tuna, golden mackerel, etc.).
With the help of a suction cup located on the head, the fish sticks to sharks, whales, 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 clings tightly to the shell of a turtle, which can only be pulled into the boat.
The Caspian lamprey attaches itself to salmon and travels upriver to its spawning grounds. Creeper fish crawls ashore at night, resting on the ground with their pectoral fins, and looking for food, such as earthworms. Another amazing fish, the mudskipper, at low tide, climbs sloping roots and tree trunks, and moves along the ground in jumps, relying on its belly and pectoral fins.
Their coloration 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, merges with the blue of the deep sea. The silvery sides and belly make the herring almost indistinguishable from below, against the backdrop of the sparkling surface of the sea. The spotted coloration of the pike is a means of camouflage in underwater thickets, where the predator usually hides, lying in wait for prey.
Bottom fish, such as sea flounder, are strikingly similar in color to the ground. Having crossed from the dark, muddy bottom to the light, sandy one, the flounder quickly brightens. Coloring is controlled by sight. If you place a flounder so that its whole body lies on a dark bottom, and its head on a light one, the fish acquires a light color.
Every amateur angler knows that a river perch caught in a clear 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 a great depth, has a bright scarlet color; lying on the deck in daylight, it gradually becomes ash-gray, and when put into a dark hold, it turns red again.
A fish with a black cover put on its eyes, as well as completely blinded, soon acquires a dark color. Tropical fish, living in a brightly lit sea among coral reefs, shine with motley 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 a muddy, rocky or shelly bottom; blue swims for a long time in the water column. As you can see, in these cases, the color of the fish is well consistent with the habitat.
However, the color of some fish from a distance is striking. For example, the back of an electric stingray is dotted with bright spots. In all likelihood, they play the role of warning signs; after all, any predator that attacked an electric stingray receives a due rebuff. Warning coloration is not uncommon among terrestrial animals that have some sort of effective means of protection - think of the wasp with its poisonous sting and black and yellow, conspicuous outfit from a distance.
A large black spot is striking on the silvery side of the haddock. There are reasons to think that it plays the role of an identification mark, helping the fish of the same flock to move together. As a rule, haddock stays in shallow areas with sandy or shell bottoms, where it is light enough to see fellow flocks.
Some fish living in the water column 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 the luminous points lie in a straight line along the ventral side of the body, somewhat resembling a row of buttons on a tunic. This fish was nicknamed "sea midshipman". The number and location of luminous spots are very characteristic for each species - they help the fish to keep track of their fellows in the flock, to find each other during the breeding season.
The scaly cover of many fish shines brightly. The bleak scales are even used to make a pearl stalemate, which is used to cover glass beads, turning them into artificial pearls. But the main features of the color of the fish still do not depend on the scales, which are generally quite transparent, but on the coloring matter - the pigment 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 generally believed that the scaly cover, like the shell, "protects the fish from enemies." But this is completely false, because almost all fish-eating predators - for example, a heron or pelican, a seal or a dolphin, a pike or a shark - swallow their prey whole. For those who 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 body of fish the elasticity, 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 that can make a clear translational movement. In fish with an elongated, serpentine body, swimming relatively slowly, the scales are very small or completely absent; such are eel, burbot, loach, catfish, catfish, gerbil, maslyuk, lumpenus.
If the scales have a protective value, then why is it absent (or very poorly developed) in all of the listed fish? The scaly cover is least developed on the ventral side of the body, although the vital organs located there, it would seem, are especially in need of protection. In a developing fry, the scales first appear in the caudal part of the body, which is understandable, since it is the caudal fin that serves as the "mover" 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 Far Eastern pink salmon migrated to the European north, local fishermen sometimes mixed it with young salmon. These fish are really similar, however, pink salmon has at least 140 scales in the lateral line, and salmon has no more than 130.
Fish are aquatic animals adapted to life in fresh water and sea water. They have a hard skeleton (bone, cartilage or partially ossified).
Consider the features of the structure and life of fish on the example of river perch.
Habitat and external structure of fish on the example of river perch
River perch lives in freshwater reservoirs (slowly flowing rivers and lakes) in Europe, Siberia and Central Asia. Water exerts a 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 head of the perch smoothly passes into the body, and the body into the tail. A mouth with lips is placed on the pointed front end of the head, capable of opening 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 are two large eyes.
perch fins
Bending the laterally flattened body and tail either to the right or to the left, the perch moves forward. When swimming, fins play an important role. Each fin consists of a thin skin membrane, which is supported by bony fin rays. When spreading the rays, the skin between them stretches and the surface of the fin increases. On the back of the perch are placed two pin fin: front big And rear smaller. The number of dorsal fins varies from species to species. At the end of the tail is a large two-lobed tail 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 paired fins(front pair of limbs) are placed at the perch on the sides of the body behind the head, ventral paired fins (rear pair of limbs) - on the underside of the body. plays a key role in moving forward tail fin. Paired fins are important when turning, stopping, moving slowly forward and maintaining balance.
The dorsal and anal fins give the fish body stability when moving forward and sharp turns.
Integument and coloration of perch
The body of the perch is covered bony scales. Each scale with its anterior edge is immersed in the skin, and with its posterior edge rests on 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 you can tell the age of the fish from them.
Outside, the scales are covered with a layer of mucus, which is secreted by the skin glands. Mucus reduces the friction of the fish's body on the water and serves as a protection against bacteria and mold.
Like most fish, the perch's belly is lighter than its back. From above, the back merges to a certain extent with the dark background of the bottom. From below, the light belly is less noticeable against the light background of the water surface.
The coloration of the perch's body depends on the environment. In forest lakes with a dark bottom, it has a dark color, sometimes even completely black perches come across there. In reservoirs with a light sandy bottom, perches live with a light and bright color. Perch often hides in thickets. Here, the greenish color of its flanks with vertical dark stripes makes the perch inconspicuous. Such a protective coloring helps him hide from enemies and better watch for the victim.
On the sides of the body of a perch from head to tail is a narrow dark lateral line. It is a kind of sense organ.
The perch skeleton 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 the perch develops in the egg, a chord appears in place of the future spine. Later, vertebrae arise around the notochord. In an adult perch, only small cartilaginous remnants between the vertebrae remain from the notochord.
Each vertebra is made up of body And upper arc ending with a long upper process. In their totality, the upper arches, together with the vertebral bodies, form the spinal canal, in which the spinal cord.
In the trunk section of the body, they are attached to the vertebrae from the side ribs. There are no ribs in the tail section; each vertebra located in it is provided with a lower arch, ending with a long lower process.
In front of the spine, the skeleton of the head is firmly articulated - scull. The skeleton is also 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 with the spine are not developed in the perch.
The skeleton is of great importance: it serves as a support for the muscles and protection for the internal organs.
Muscles of river perch
Muscles attached to bones are located under the skin. muscles. The strongest of them are located on the dorsal side of the body and in the tail section.
The contraction and relaxation of the muscles causes the body of the fish to bend, due to which it moves in the water. In the head and near the fins there are muscles that move the jaws, gill covers and fins.
Swim bladder of a river perch
River perch, like any fish, is heavier than water. Its buoyancy provides swim bladder. It is located in the abdominal cavity above the intestines and has the form of a translucent sac filled with gas.
Figure: The internal structure of a 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 contact with the gut at 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 adjusting the volume of the swim bladder, the perch stays at a certain depth, emerges or sinks. When the bubble is compressed, excess gas is absorbed by the blood in the capillaries of the inner surface of the bubble. If the bubble expands, then the gas enters it from the blood. As 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 bubble does not change. This allows the fish to stay motionless, as if hanging in the water column.
Unlike river perch, in other fish, such as carp, bream, roach, herring, the swim bladder maintains contact with the intestine through 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 to the fish. In addition, it helps fish hear better, because, being a good resonator, it amplifies sounds.
Laboratory work
Fins and types of movement of fish
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 (perch, crucian carp, bream, sea flounder, etc.)
Material and equipment
Frozen fish: Russian sturgeon, goldfish, perch; sea flounder, bream, etc.; fixed material of sturgeons and teleosts, dummies, posters and drawings; metal cuvettes, tweezers, scalpels, dissecting needles and scissors, calculator (computer).
General position
Fins. Their sizes, shape, number, position and functions are different. The fins allow you to maintain the balance of the body, participate in the 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) fatty ar (( p.adiposa).
Salmonids, characins, killer whales, and others have a adipose fin(Fig. 2), devoid of fin rays ( p.adiposa).
Rice. 2 Adipose fin
Pectoral fins common in bony fish. In stingrays, the pectoral fins are enlarged and are the main organs of movement.
Pelvic fins occupy a different position in fish, which is associated with a shift in the center of gravity caused by contraction of the abdominal cavity and the concentration of viscera in the anterior part of the body.
Abdominal position– ventral fins are located in the middle of the abdomen (sharks, herring-like, cyprinids) (Fig. 3).
Rice. 3 Abdominal position
Thoracic position- ventral fins are shifted to the front of the body (perch-like) (Fig. 4).
Rice. 4 Thoracic position
jugular position- ventral fins are located in front of the pectorals and on the throat (cod) (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 herring-like, 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, the cod has two, the spiny shark does not have it.
tail fin has a varied structure.
Depending on the size of the upper and lower blades, there are:
1)isobath type - in the fin, the upper and lower lobes are the same (tuna, mackerel);
Rice. 6 Isobath type
2)hypobatic type – elongated lower lobe (flying fish);
Rice. 7 Hypobatic type
3)epibat type – lengthened upper lobe (sharks, sturgeons).
Rice. 8. Epibatic type
According to the 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 lobe of the fin (sharks, sturgeons) (Fig. 10).
Rice. 10 Heterocercal type;
3) homocercal type - outwardly symmetrical, while the modified body of the last vertebra enters the upper lobe (bony) (
Rice. 11 Homocercal type
The fin rays serve as support for the fins. In fish, branched and unbranched rays are distinguished (Fig. 12).
Unbranched fin rays can be:
1)jointed (capable of bending);
2)non-segmented hard (prickly), 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 thorny rays is indicated by Roman numerals, branched - by Arabic. For example, the dorsal fin formula for a river perch is:
DXIII-XVII, I-III 12-16.
This means that the perch has two dorsal fins, of which the first consists of 13 - 17 spiny, the second of 2 - 3 spiny and 12-16 branched rays.
Fin functions
· tail fin creates a driving force, provides high maneuverability of the fish when turning, acts as a rudder.
· Thoracic and abdominal (paired fins ) maintain balance and are rudders when cornering and at depth.
· dorsal and anal the fins act as a keel, preventing the body from rotating around its axis.
Ways of movement of fish
The variety of living conditions of fish determines the ways of their movement. Fish have three 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 with the help of lateral bends of the body:
Mackerel- in fish when swimming, the tail is of great importance, with the help of which the fish repels from the water and moves forward, which accounts for about 40% of the entire driving force (mackerel, salmon).
Acne (serpentine)- in fish, when moving, the whole body bends in waves. This is the most economical type of movement, while the swimming speed is low (lamprey, eel, loach).
Fish swim at different speeds. The fastest is swordfish, capable of speeds up to 33 m/s (118.8 km/h), tuna swims at speeds 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 the length of the body. Accordingly, it is determined speed factor - the ratio of the absolute speed to the square root of its length:
According to the speed of movement, the following groups of fish are distinguished:
1) very fast (swordfish, tuna) - speed coefficient about 70;
2) fast (salmon, mackerel) - 30–60;
3) moderately fast (mullet, cod, herring) - 20–30;
4) slow (carp, bream) - 10–20;
5) slow (steers) - 5–10;
6) very slow (stickleback, moonfish) - 5.
Fish of the same species can swim at different speeds. Distinguish:
1. Throwing speed(speed factor 30–70), which
develops within a very short time (when frightened, throwing at prey).
2. Cruise speed(speed factor 1–4) at which the fish swim for a long time.
Crawl on the ground is one of the ways of movement of fish, which is carried out mainly with the help of pectoral fins and tail (creeper, monkfish, multifin, jumper, gurnard). So, the jumper lives in the mangroves and spends much of his time on the shore. On land, it moves by jumps, 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 pelagial of tropical and subtropical waters of the oceans. These fish have long and wide pectoral fins that act as wings. The tail with a strongly developed lower blade is the engine that gives the initial speed. Having jumped to the surface of the water, the flying fish glides over the water surface for the first time, with an increase in the speed of movement it breaks away from the water, flying at the same time a distance of up to 200 and even 400 m.
Working process
1. Get acquainted with the content of the theoretical material set out in the guidelines.
2. Consider the shapes, types, location and structure of the fins of fish prepared for laboratory work. Schematically depict salmon and highlight paired and unpaired fins on the diagram. Name the functions of the various fins.
3. List the different positions of the pelvic fins and give examples.
4. List and sketch the types of caudal fins in structure and in shape and location relative to the end of the spine.
5. Consider the structure of the dorsal fins of the perch, select non-branched (spiky) and branched (segmented) 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 factor - the ratio of absolute speed to the square root of its length. If necessary, convert the speed to km/h.
for the 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).
Test questions:
1. Functions of fish fins
2. Shapes, types, location and structure of fish fins
3. Ways of movement of fish.
4. Give a definition of cruising and throwing speeds, give examples.
5. How is the fish speed factor calculated?
Vasilyeva E.D., Luzhnyak V.A. Fishes of the Sea of Azov basin [Ch. ed. acad. G.G. Matishov]. - Rostov n / D: Publishing House of the YuNTs RAS, 2013. - 272 p.
Ivanov V.P., Egorova V.I. Fundamentals of ichthyology: textbook. allowance. Astrakhan. state tech. un-t. - 2nd ed., add. and clarification - Astrakhan: Publishing House of ASTU, 2008. - 336 p.
Ivanov V.P., Komarova G.V. Fishes of the Caspian Sea (systematics, biology, fishing). Astrakhan. State Technical University - 2nd ed., supplement. and clarify. - Astrakhan: Publishing House of ASTU, 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.: Legk. 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 movement of fish
Guidelines for laboratory work
in the discipline "Ichthyology"
DSTU Publishing Center
University and printing company address:
344000, Rostov-on-Don, pl. Gagarina, 1
1. Tail fin creates a driving force, provides high maneuverability of the fish when turning, acts as a rudder.
2. Paired fins ( thoracic, abdominal) maintain balance and are rudders when cornering 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 bearing planes; it includes the pectoral and ventral fins (if they are under the pectoral or in front of them);
2nd zone- keel; it includes the dorsal fin located in front of the center of gravity, as well as the pelvic fins, if they are in front of the center of gravity; if there is one dorsal fin (as in herring and cyprinids), this zone includes its front part, if there are several, then the first;
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, as well as the adipose fin (if any); in cod, for example, this zone includes the second dorsal and first anal, in salmon - adipose and anal fins;
4th zone- rear rudders and locomotor body; it includes the caudal fin and, in most fish, the back of the dorsal and anal fins; in cod, this zone includes the third dorsal and second anal fins; this zone includes additional fins that some fish have behind the dorsal and anal fins (mackerels) (Fig. 6).
Rice. Fig. 5. Functional areas of the fins and their position during rectilinear movement (A) and when turning (B)(according to Aleev):
salmon; 2 - bonito; 3 - cod.
In rectilinear motion, the fins I and II zones in most fish do not function and are pressed to the body (numbers in brackets indicate that the function of this zone for this fin is not the main one).
Movement methods. The variety of living conditions of fish determines the ways of their movement. Fish have three 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 a fish with a large number of vertebrae is more strongly bent. The short body of the fish moon (17 vertebrae in total) cannot bend. Fish, in which the body structure excludes the possibility of lateral bends, swim with the help of wave-like movements of the fins: electric eel - anal; moon-fish and boxfish - tail; slopes of the chest.
Distinguish two types of swimming with side bends
1. mackerel - in fish when swimming, the tail is of great importance, with the help of which the fish repels from the water and moves forward, which accounts for about 40% of the entire driving force (mackerel, salmon).
2eel (serpentine) - in fish, when moving, the whole body bends in waves. This is the most economical type of movement, while the swimming speed is low (lamprey, eel, loach).
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Rice. 5. Types of swimming a) mackerel, c) eel
Rice. 7. The movement of fish with the help of wave-like movements of the fins (according to Aleev):
1 - moon-fish; 2- box; 3 - electric eel; 4 - flounder.
Those fish in which the body structure excludes the possibility of lateral bends (bodywork, bluehorn, seahorse, needle-fish, moon-fish, electric fish) swim with the help of wave-like (undulating) movements of the vertebrae: electric eel; moon-fish and boxfish - tail; stingrays - chest
There are two types of swimming with the help of lateral bends
Fish swim at different speeds. The fastest is swordfish, capable of speeds up to 33 m/s, tuna swims at speeds up to 20 m/s, salmon - 5 m/s.
The speed of movement of fish is also dependent 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).
According to the speed of movement, the following groups of fish are distinguished:
1) very fast (swordfish, tuna) - speed coefficient about 70;
2) fast (salmon, mackerel) - 30–60;
3) moderately fast (mullet, cod, herring) - 20–30;
4) slow (carp, bream) - 10–20;
5) slow (steers) - 5–10;
6) very chalky (stickleback, moonfish) - 5.
Fish of the same species can swim at different speeds. Distinguish:
1. Throwing speed(speed factor 30–70), which
develops within a very short time (when frightened, throwing at prey).
2. cruising speed(speed factor 1–4) at which the fish swim for a long time.
The speed of fish movement depends on the structural features (body shape, scale cover, presence of mucus), physiological state, water temperature and other factors. Slowly swimming fish are characterized by a high body and large scales (cyprinids), as well as an eel-like, ribbon-like, spherical body shape. Fast-swimming fish have a well-streamlined body shape, small scales, a thin muscular caudal peduncle, often with lateral keels (swordfish, tuna), a strongly 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 (mullets), elongated scales on the tail (black-backed herring), etc.
fish swim in a horizontal position, however, differences are observed in some species. The seahorse moves upward along a helical line, working with its dorsal and pectoral fins, and wave-like bends the caudal stalk, devoid of a caudal fin. The cranktail, gathering in flocks, swims in an upright position. Cirrus catfish of African rivers swim slowly at the surface of the water with their belly up. Passive movement of fish (fish-stuck) can be attributed to special forms of swimming.
Crawl on the ground is one of the ways of movement of fish, which is carried out mainly with the help of pectoral fins and tail (creeper, monkfish, multifin, jumper, gurnard). So, the jumper lives in the mangroves and spends much of his time on the shore. On land, it moves by jumps, 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 pelagial of tropical and subtropical waters of the oceans. These fish have long and wide pectoral fins that act as wings. The tail with a strongly developed lower blade is the engine that gives the initial speed. Having jumped to the surface of the water, the flying fish glides over the water surface for the first time, with an increase in the speed of movement it breaks away from the water, flying at the same time a distance of up to 200 and even 400 m.
To get food and escape from enemies, fish must move in a dense body of water. Therefore, they all have a streamlined body shape, which makes it easier for them to overcome the resistance of water. Between the head, trunk and tail there are no protrusions and transitions and there is no clear boundary. The wedge-shaped head, adapted to cut through the water, is motionlessly articulated with the spine.
Fish that make long journeys or constantly live in the rapids have the most perfect streamlined shape - their body is valky or spindle-shaped and is equipped with a powerful tail. Fish that live in calm waters have a high body, adapted to a quick change in direction of movement. They differ in the shape of the body of fish living at the bottom (they are, as it were, flattened) and in the upper layers of water (with flat sides).
The nature of the diet of fish also affects the shape of the body. Predators have a longer and more agile body, forced to catch up with prey. Fish that eat sedentary food are shorter than predators in length, but significantly exceed their body height.
The main motor organ of fish is the tail, with the help of which they seem to repel water. In most of our fish, the tails are equipped with two-lobed fins; in catfish, burbot and some others, the tail fin is single-lobed.
In addition to the caudal fin, there are two pectoral fins located not far from the head on both sides of the body, and behind them and a little lower - two ventral fins. The unpaired caudal fin is located on the belly behind the anus. On the back there are two (perch, zander) or one (pike) dorsal fin.
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 caudal are a kind of keels that regulate the position of the body of the fish in a vertical plane. The pectoral and ventral fins make it easier for the fish to move up and down and during turns.
Outside, the entire body of the fish is covered with a thin flexible shell formed by bone plates - scales. Scales are of three types. In carp (white) fish - they have a rounded front edge; in the skin, such scales sit loosely and easily fall off.
Perch scales have teeth; they sit very firmly in the skin. The body of sturgeons is covered with scales with a protruding tooth in the middle.
The size of the scales increases with the growth of the fish. But this happens not due to the expansion of the existing plate, but due to the appearance under it of a new young scale of a larger size. In other words, as the age of the fish increases, the scales increase in both width and thickness. It becomes like a stack of superimposed and fused thin plates, of which the top is the oldest and smallest, and the bottom 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 carefully cleaned of skin and mucus remnants and placed under a loupe of 8-10 times magnification. Concentric rings visible in a magnifying glass are the edges of all gradually formed plates.
But the growth of fish, and hence the growth of scales, is uneven throughout the year. In summer, the fish actively feeds and grows faster, so the distances between the edges of the plates are the widest. In the autumn, due to the slowdown in the growth of fish, they narrow. And in winter they approach so much that they form one dark ring. The following summer, new wide concentric rings appear on the record, narrowing towards autumn and winter. Therefore, the number of dark rings on the scales of the fish 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 plays 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 the fish to move faster in the water column with a low consumption of muscle energy. It is located in the body cavity under the spine and communicates with the pharyngeal cavity in some fish, and with the anus in others. In order to go to depth, the fish releases part of the gas located there from the bubble.
