Probably, every person, looking at the aquarium, experiences some strange feelings. It is both peace and relaxation. Has anyone been fishing? You must remember these sensations, this excitement, sports interest. Also, many people have always been interested in knowing what fish swim with, how do they do it? Therefore, in order to understand how fish swim, it is necessary to understand their anatomy in more detail.

Inside the fish is a swim bladder, which is a film organ. This organ is connected to the intestines of the fish. To move in the water, the fish regulates the amount of gas in its swim bladder.

The density of the body of the fish is equal to the density of water, so the fish is additionally kept in a vertical floating position due to this feature of its body. Also, each representative of this series of wildlife in the water depths regulates its movement due to fins.

Fish adaptations

stay in vertical position the dorsal and anal fins help the fish, while the pectoral fins propel the fish forward. The tail also explains why fish swim. It functions like:

• The main "engine" of the fish.

The muscles that are located along the body of the fish also help it move in the water. When a fish wiggles its whole body, it tenses and relaxes the muscles on one side and then on the other. This is how the swimming movement occurs, which resembles the movement of a snake.

Thus, a whole system and mechanism of organs operates in a fish so that it can swim. There are some other structural features of the fish body that help it move faster and easier:

• The body of each fish has a smooth and smooth outline, which reduces water resistance when moving.
• The skin of the fish is covered with a special mucus, which adds gliding and smoothness in movement.

Fast-swimming fish have the same properties as regular fish, but their muscles are stronger and their fins are larger and more agile. Therefore, the fish can develop speed, which helps to hunt smaller fish and quickly get away from predators.

Constantly on the move

Sharks and sailboats do not have swim bladders, so they have to stay in the water only due to their pectoral fins. They perform the same functions as the wings of an airplane. In order not to drown, the fish have to constantly be in a state of movement.

Bottom views

Bottom fish species very rarely emerge into the water column, because there they are immediately noticeable and attractive to predators. These fish have a flattened back, because they do not have to constantly swim. These species are represented by gobies, flounder, stingrays and stargazers. Completely flat fish, such as stingrays, are the type of aquatic inhabitants that have turned their fins into the sides of the body. Therefore, they manage to swim thanks to the waves that run through their flat outlines of the body.

But fish that are in constant motion, among the expanses of water, have a flattened body and head on the sides. Such fish move forward by bending their body like a spring. All their efforts are a movement, a contraction of all the lateral muscles of the body, which is focused on each stroke of the tail. So fish swim near the surface of the water, looking for small plankton, or swim away from predators, or they can simply calmly cut through the water column.

Atypical swimming

If the fish swims belly up, there may be several factors involved:

• binge eating;
• disease of various kinds;
• death.

There are also special types of swimming, among the representatives of fish: sea needles and seahorses have turned their tail fins into a regular tail. Therefore, they carry out movement due to their dorsal fins. The world of fish is very diverse, there are its representatives who not only swim, but also walk along the bottom, like, for example, gurnards and dogs.

Take a closer look at the movements of the fish in the water, and you will see which part of the body takes the main part in this (Fig. 8). The fish rushes forward, quickly moving its tail to the right and left, which ends in a wide caudal fin. The body of the fish also takes part in this movement, but it is mainly carried out by the tail section of the body.

Therefore, the tail of the fish is very muscular and massive, almost imperceptibly merges with the body (compare in this respect with terrestrial mammals like a cat or dog), for example, in a perch, the body, inside which all the insides are enclosed, ends only a little further than half the total length of its body, and everything else is already his tail.

In addition to the caudal fin, the fish has two more unpaired fins - the dorsal fin on top (in perch, pikeperch and some other fish it consists of two separate protrusions located one after the other) and the bottom caudal, or anal, which is called so because it sits on the underside of the tail, just behind the anus.

These fins prevent the rotation of the body around the longitudinal axis (Fig. 9) and, like the keel on a ship, help the fish maintain a normal position in the water; in some fish, the dorsal fin also serves as a reliable defense tool. It can have such a value if the fin rays supporting it are hard prickly needles that prevent a larger predator from swallowing fish (ruff, perch).

Then we see more paired fins in the fish - a pair of pectoral and a pair of abdominal ones.

The pectoral fins sit higher, almost on the sides of the body, while the pelvic fins are closer to each other and are located on the ventral side.

The location of the fins various fish unequally. Usually, the ventral fins are behind the pectorals, as we see it, for example, in pike (gastro-finned fish; see Fig. 52), in other fish, the ventral fins have moved to the front of the body and are located between the two pectorals (breast-finned fish, Fig. 10) and, finally, in burbot and some marine fish, such as cod, haddock (Fig. 80, 81) and navaga, the ventral fins sit in front of the pectoral, as if on the throat of a fish (throat-finned fish).

Paired fins do not have strong musculature (check this on dried wobble). Therefore, they cannot affect the speed of movement, and the fish row them only during the slowest movement in a calm standing water(carp, crucian, goldfish).

Their main purpose is to maintain the balance of the body. A dead or weakened fish topples with its belly up, since the back of the fish is heavier than its ventral side (why - we will see at the autopsy). This means that a living fish has to make some effort all the time so as not to tip over on its back or fall on its side; this is achieved by the work of paired fins.

You can verify this by a simple experiment, depriving the fish of the opportunity to use their paired fins and tying them to the body with woolen threads.

In fish with tied pectoral fins, the heavier head end pulls and falls down; fish whose pectoral or ventral fins are cut off or tied on one side lie on their side, and the fish, in which all paired fins are tied with threads, tip over belly up as if dead.

(Here, however, there are exceptions: in those species of fish in which the swim bladder is located closer to the dorsal side, the belly may be heavier than the back, and the fish will not roll over.)

In addition, paired fins help the fish make turns: wanting to turn to the right, the fish grabs the left fin, and presses the right fin against the body, and vice versa.

Let us return once again to clarify the role of the dorsal and caudal fins. Sometimes, not only in the answers of the students, but also in the explanations of the teacher, the matter appears as if it is they who give the body a normal position - with the back up.

In fact, as we have seen, this role is played by paired fins, while the dorsal and caudal fins, when moving the fish, prevent its spindle-shaped body from spinning around the longitudinal axis and thereby maintain the normal position that the paired fins gave to the body (in a weakened fish swimming on its side or belly up, the same unpaired fins support the abnormal position already taken by the body).

ABOUT general information about fish.

going on fishing, every angler asks himself a series of questions: where to go? what tackle to take? which nozzle to use? Additional questions arise on the pond: where to fish - at depth or near the shore? in calm or current? from the bottom, on top or in half water? etc.

All of these questions are significant. After all, the success of fishing depends on their correct decision. But finding such a solution is not always easy. The study of the literature can provide only partial help, since the behavior of fish in different water bodies depends on changing environmental conditions.

The decisive moment is the direct study of the reservoir and the fish living in it. In this case, conversations with local fishermen can be used, but the main thing, of course, is personal observations.

That is why the angler must have a general idea of ​​how the environment affects the behavior of fish, their food; he needs to understand questions of general biology and have elementary information about the structure and work of individual organs of fish.

This chapter highlights some issues of general fish biology that are directly related to sport fishing. The presentation is based on data from special ichthyological literature, as well as personal observations of the author.

The structure of the body of fish and their movement.

Modern biological science teaches what certain organisms are inherent in a certain environment. The study of fish biology clearly confirms this position. The organism of fish, starting from the shape of the body and ending with the respiratory apparatus and sensory organs, is adapted to the conditions of life in the water.

Fish need to move in order to find food and escape from enemies. However, water provides significant resistance to their movement. Therefore, in the process of evolution, most fish acquired a streamlined body shape, which makes it easier to overcome the resistance of the aquatic environment.

The most perfect streamlined shape of the body are anadromous fish that make long migrations, such as salmon. Almost the same valky or spindle-shaped body, powerful tail and medium-sized scales in fish that constantly live in the rapids (trout, minnow, osman, barbel, etc.). Sometimes some fish (roach, ide) living in the upper reaches of the river on fast current, have a more valky body than fish of the same species inhabiting the mouth, where the current is slower. Wide, high-bodied fish live in calm waters, since here they do not have to fight the current; in addition, this body shape helps them better avoid predators that are less willing to grab wide fish.

The forms of the body are also different in fish that live at the bottom and in the upper layers of the water. For example, in bottom fish (flounder, catfish, burbot, goby) the body is flattened, allowing them to rest on the ground with a large surface.

Sometimes fish adapt to passive movement. The leaf-like shape of eel larvae facilitates their transfer by current from eel spawning sites located off the coast of Central America to permanent habitats in European water bodies.

In cases where the fish almost do not move, part of their body, together with the tail, turns into an attachment organ (seahorse).

The nature of nutrition also has a certain influence on the shape of the body; for example, at predatory fish catching prey, the body is usually more agile than that of fish feeding on sedentary food.

The mechanism of fish movement remained unclear for a long time. It was assumed that the fins play the main role here. Latest research physicists and ichthyologists proved that forward movement fish is carried out mainly by wavy bends of the body. The caudal fin provides some assistance in moving forward. The role of other fins is reduced mainly to coordinating and guiding functions - the dorsal and anal fins serve as a keel, the pectoral and ventral fins make it easier for the fish to move vertically and help turn in a horizontal plane.

Breath.

Most fish breathe oxygen dissolved in water. The main respiratory organ is the gills. The shape and size of the surface of the gills, the structure of the gill slits, and the mechanism of respiratory movements depend on the way of life of the fish. In fish swimming at half-water, the gill slits are large, and the gill filaments are constantly washed by fresh, oxygen-rich water. In bottom fish - eel, flounder - gill slits are small (otherwise they can become clogged with silt) with devices for forced circulation of water.

Fish that live in oxygen-poor water have additional respiratory organs. Carp and some other fish, when there is a lack of oxygen in the water, swallow atmospheric air and use it to enrich the water with oxygen.

Tench, catfish and eel have additional cutaneous respiration. In the respiratory functions of the perch, the swim bladder is involved, and in the loach, the intestines. Some warm-water fish are endowed with organs that allow them to breathe directly from atmospheric air. In some fish, this is a special labyrinth apparatus, in others it is a swim bladder that has turned into a respiratory organ.

According to the structure respiratory organs fish have different attitudes to the amount of oxygen dissolved in water. Some fish need a very high content of it in the water - salmon, whitefish, trout, pike perch; others are less demanding - roach, perch, pike; still others are satisfied with a completely negligible amount of oxygen - crucian carp, tench. There is, as it were, a threshold for the oxygen content in the water, defined for each species of fish, below which individuals of a given species become lethargic, hardly move, feed poorly, and eventually die.

Oxygen enters the water from the atmosphere and is released by aquatic plants, and the latter, on the one hand, release it under the action of light, and on the other, they absorb it in the dark and spend it during decay. Therefore, "the positive role of plants in the oxygen regime is noticeable only during their growth, i.e., in summer, and, moreover, during the day.

From atmospheric air, water is enriched with oxygen around the clock. The intensity of oxygen dissolution depends on the temperature of the water, the size of the water surface in contact with air, and the mixing of various layers of water. The lower the temperature, the larger the water surface and the more intense the mixing, the better oxygen dissolves in water. Therefore, in the summer, a decrease in temperature and strong winds contribute to the improvement of the well-being of fish, especially in water bodies with insufficient oxygen content. After the rain, the activity of the fish also intensifies and the bite revives. Oxygenated raindrops increase the total oxygen content in the reservoir.

Oxygen slowly penetrates from one water layer to another, and there is always more oxygen in the surface layers than near the bottom. This is one of the reasons for the poor development of life and the absence of accumulation of fish in the summer at depths, especially in stagnant water bodies.

In lakes there are areas with higher and lower oxygen concentrations. For example, the wind blowing from the shore drives away the oxygen-rich upper layers of water, and in their place comes low-oxygenated deep water. Thus, a zone that is poorer in oxygen content is created near the calm coast, and the fish, other things being equal, prefer to stay near the surf coast. A typical example is the behavior of the oxygen-loving grayling in Lake Ladoga, which approaches the shore mainly when there is a steady wind blowing from the lake.

The oxygen regime deteriorates sharply in stagnant water bodies in winter, when the ice cover prevents air from reaching the water. This is especially noticeable in shallow, heavily overgrown water bodies with a muddy or peaty bottom, where the oxygen supply is spent on the oxidation of various organic residues. In winter, zones with unequal oxygen content are found in lakes even more often than in summer.

Areas with a rocky or sandy bottom, at the exit of spring waters, at the confluence of streams and rivers are richer in oxygen. These places are usually chosen by fish for winter parking. In some lakes, especially during severe winters, the oxygen content in the water drops so much that mass death fish - the so-called zamora.

In rivers, especially fast-flowing ones, there is no sharp natural lack of oxygen either in summer or in winter. However, in rivers clogged with timber floating waste and polluted with industrial wastewater, this deficiency is so great that oxygen-demanding fish completely disappear.

Movement of fish, amphibians and reptiles

Vertebrates are a perfect group of animals that have mastered all three environments: land, water and air. We now turn to the consideration of the methods of movement of this group of animals.

Without exception, all fish live in water and have learned to move well in it. The streamlined body of most fish is torpedo-shaped; the absence of protruding parts and the lubrication of the scales minimize water resistance during movement. The movement of the body forward occurs due to the lateral movements of the tail. The caudal fin curves and repels the water; the longitudinal component of the water resistance force pushes the fish forward. In fish with a sufficiently long body, not only the tail, but also the back of the body helps to swim forward. Finally, in long eels, parts of the body bend in different directions. The curves are created by contraction of the myotomes, blocks of muscles located on either side of the spine.

Sharks that do not have a swim bladder must always be in motion or they will sink to the bottom. Their pectoral and pelvic fins, when moving, create additional lifting force, under the influence of which the fish can rise or fall in the water column. The deviation of the fish from the equilibrium position is corrected vertically by the pectoral and ventral fins, and horizontally by the dorsal fins. The bank angle is stabilized by all fins at once. Nerve impulses aimed at stabilization come from the semicircular canals to the brain, and from there are delivered to the fins.

swim bladder bony fish provides neutral buoyancy; the density of the fish is equal to the density of the surrounding water, and it does not need to expend energy to maintain the body in the water. In this regard, the pectoral and pelvic fins have become smaller and serve to provide stability or for braking (in the latter case, they straighten at right angles to the body). The independence of the pectoral fins allows the fish to make a quick turn relative to one of them. The symmetrical caudal fin pushes the body forward.

The swim bladder is filled with air, but the percentage composition of gases may differ from atmospheric. Meet open and closed swim bladders. The first are connected to the esophagus; regulation of the amount of air is carried out through the mouth. The latter are not connected with the esophagus; air enters the bladder as needed and is absorbed from it through the circulatory system.

Some fish have learned to crawl on land (ancient lobe-finned fish) or fly (for example, flying fish). However, this flight is “fake”: a flying fish jumps out of the water and, due to its speed, “flies” up to 200 m. At the same time, its fins create a lifting force that helps the fish stay in the air for some time. However, neither air nor land became a common habitat for fish.

After the appearance of lobe-finned fish on land, the fins were transformed into real limbs. In ancient amphibians, they were attached to the body from the side, which made it possible for them to crawl without leaving the ground. In more progressive vertebrates, a tendency was found to shift the limbs downward. The weight of the body was distributed evenly between the limbs, and the animal spent much less energy on maintaining its body.

The frog's paired legs are actually jointed levers that lift the body above the ground and ensure its movement. When moving slowly along the ground, the limbs located diagonally from each other are simultaneously extended forward; a pair of limbs on the other diagonal is bent. These limbs pull the body of the frog forward, after which the other pair of limbs unbends.

When jumping, all joints of the hind limbs are extended simultaneously. The repulsive force is several times greater than the weight of the frog and is quite sufficient for the frog to jump forward and upward. During landing, the short forelegs provide cushioning and soften the impact.

Many forms of amphibians and reptiles can swim well, and for the extinct ichthyosaurs and plesiosaurs, water was a natural habitat. Another ancient form of reptile, pterosaurs, were able to fly using flapping flight and sometimes soaring on membranous wings in ascending air currents.

There are quite a variety of ways to move snakes. Usually they crawl along the surface at a speed of several kilometers per hour, bending S-shaped in a horizontal plane. Forward movement is ensured by repulsion by the back surface of the bends from the unevenness of the soil. crawl over smooth surface snakes cannot do this, but this method is well suited for swimming. The ability to hold your breath for a long time greatly facilitates movement in the water.

Large snakes crawl like caterpillars due to undulating contractions subcutaneous muscles. The shields on the belly of the animal are repelled by the uneven surface of the soil, and the snake crawls in a straight line. On loose sands, snakes use a "lateral move". Either the front or the back parts of the body are thrown forward in turn, the snake, as it were, jumps on the sand, keeping sideways to the direction of movement. In conclusion, we note that most snakes climb trees quite well.

Nature acted very wisely when it endowed fish with special devices that help the inhabitants of reservoirs overcome the resistance of water while moving in its thickness. Of course, decorative aquarium fish also have them.

Over the hundreds of millions of years that fish have existed on our planet, it can be said with confidence that they, like no other, as a result of their long evolution, have acquired many tricks and "secrets" that allow these amazing representatives of the underwater fauna to use their natural habitat. One of these secrets is precisely the ability to move in water for a long time and with high speed without feeling tired and without wasting the accumulated energy.

Fish locomotion, speed and endurance

Fish are characterized by such modes of movement as swimming, crawling, flying. We are interested in the first method, because it is inherent in the overwhelming species of fish. However, these species can also fly (for example, if they jump out of the aquarium in a panic from a predator chasing them) and crawl when, having plopped down on the floor, they continue to move on land.

We are still interested in the swimming speed of fish and their endurance. For swimming fish, regardless of their habitat (Lake Titicaca or a home aquarium), four types of speed are characteristic - throwing, maximum, cruising, intermediate.

• with a throwing speed, the fish rush to the prey and escape from the detected obvious close threat. Ichthyologists have established that fish cannot swim at such a speed for a long time - only some fractions of a second. After being thrown, they reduce their movement speed to maximum,
• on the top speed fish "run away" from the mouth of a predator. They are able to keep it, depending on their size and structure, from 20 seconds (decorative aquarium fish) up to several minutes (larger in size and muscle development, the inhabitants natural reservoirs: rivers, seas, oceans),
• tired, the fish move to cruising speed, which they are able to maintain for quite a long time,
• at an intermediate speed (or normal), the fish cannot swim constantly, because its behavior in the water is constantly changing: either it saw a piece of food and made a throw after it, or it saw the danger from a large neighbor in the aquarium, or something else forced fish "switch" to a different speed.

Pisces, like us humans, have one pattern: the faster we move, the sooner we get tired. As ichthyologists have established, small fish are much more enduring and their muscles are better adapted to the frequent “switching” of speeds.

What contributes to the fact that the fish move quickly and do not get tired:

• the streamlined shape of the body helps the fish to gain great speed. If the inhabitants of the aquarium are properly selected and nothing threatens the miniature fish, if they ever need to resort to throws and maximum speed, it is extremely rare, since the owner of the aquarium makes sure that there is enough food for everyone. One way or another, in the pursuit of food, those fish are ahead of their rivals, the body of which has an elongated streamlined shape, better resisting water resistance. In this regard, there is nothing surprising in the fact that in nature the sailboat living in the western waters of the Pacific and the tropical waters of the Indian Ocean is recognized as the record holder among fish in speed. The fish owes its name to the dorsal fin in the form of a sail. Scientists have found that this fish is capable of a short time develop speed up to 110 km / h. Of land animals, such speed is too tough even for a swift-footed cheetah. The sailfish owes such agility, first of all, to the structure of its body;
• The mucous substance secreted by the skin of fish reduces the force of water resistance. The release of such a mucous lubricant is typical for most types of fish (marine, freshwater, commercial, ornamental). The more mucus a fish produces, the faster it swims. Such natural lubrication smooths out all the irregularities on the body of the fish and reduces the friction of the body of the fish on the water;
• fins and tail contribute to the conservation of strength in fish and save energy,
• thanks to the gills, the flow of oxygen to the vessels increases. They, in turn, supply the gills of fish with blood, which enhances the supply of oxygen to muscle tissue cells of underwater inhabitants.

All these anatomical, biological and physiological features of fish are necessary for them to save energy during relentless constant movement in the water.