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 fish’s tail is very muscular and massive, almost imperceptibly merging with the body (compare in this regard with terrestrial mammals like a cat or dog), for example, in a perch the body, which contains all the insides, 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 - on top of the dorsal (in perch, pike perch and some other fish it consists of two separate protrusions located one behind the other) and below the subcaudal, or anal, which is so called because it sits on the underside of the tail, just behind the anus.
These fins prevent the body from rotating around the longitudinal axis (Fig. 9) and, like a 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 weapon of defense. It can have this significance if the fin rays supporting it are hard, prickly needles that prevent a larger predator from swallowing the fish (ruff, perch).
Then we see the fish have more paired fins - 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 together and located on the ventral side.
The location of the fins varies among different fish. Usually the pelvic fins are located behind the pectoral fins, as we see, for example, in pike (gastrofinned fish; see Fig. 52), in other fish the pelvic fins have moved to the front of the body and are located between the two pectoral fins (pectoral finned fish, Fig. 10) , and finally, in burbot and some marine fish, such as cod, haddock (Fig. 80, 81) and navaga, the pelvic fins sit in front of the pectoral fins, as if on the throat of the fish (throat-finned fish).
The paired fins do not have strong muscles (check this on a dried roach). Therefore, they cannot influence the speed of movement, and fish row with them only when moving very slowly in calm, standing water (carp, crucian carp, goldfish).
Their main purpose is to maintain body balance. A dead or weakened fish turns over with its belly up, since the back of the fish turns out to be heavier than its ventral side (we will see why during 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 to its side; this is achieved by the work of paired fins.
You can verify this through a simple experiment by depriving the fish of the opportunity to use its paired fins and tying them to the body with woolen threads.
In fish with tied pectoral fins, the heavier head end is pulled and lowered; fish whose pectoral or ventral fins are cut off or tied on one side lie on their sides, and a fish in which all paired fins are tied with threads turns upside down, 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 turn over.)
In addition, paired fins help the fish make turns: when wanting to turn to the right, the fish paddles with the left fin, and presses the right one to the body, and vice versa.
Let us return once again to clarify the role of the dorsal and subcaudal fins. Sometimes, not only in the students' answers, but also in the teacher's explanations, it seems as if they are the ones who give the body a normal position - back up.
In fact, as we have seen, paired fins perform this role, while the dorsal and subcaudal fins, when the fish moves, prevent its fusiform body from spinning around the longitudinal axis and thereby maintain the normal position that the paired fins gave the body (in a weakened fish swimming on its side or belly up, the same unpaired fins support the abnormal position already assumed by the body).
ABOUT general information about fish.
When going fishing, every angler asks himself a number of questions: where to go? what tackle should I take? Which attachment should I use? On a reservoir, additional questions arise: where to fish - at depth or near the shore? in still water or on the current? from the bottom, on top or in mid-water? etc.
All these questions are significant. After all, the success of fishing depends on their correct decision. But finding such a solution is not always easy. Studying the literature can only provide partial help, since the behavior of fish in different bodies of water depends on changing environmental conditions
The decisive point 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 fisherman must have a general understanding of how the environment influences the behavior of fish and their nutrition; he needs to understand issues of general biology and have basic information about the structure and functioning of individual organs of fish.
This chapter covers 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 body structure 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 body of fish, from the shape of the body to the respiratory apparatus and sensory organs, is adapted to living conditions in water.Fish need to move 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, making it easier to overcome the resistance of the aquatic environment.
The most perfect streamlined body shape is found in migratory fish that make long migrations, such as salmon. Almost the same ridged or spindle-shaped body, powerful tail and medium-sized scales are found in fish that constantly live in the rapids (trout, minnow, osman, barbel, etc.). Sometimes some fish (roach, ide) that live in the upper reaches of a river in a fast current have a more ridged body than fish of the same species that inhabit the mouth, where the current is slower. Wide, tall-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 who are less willing to grab wide fish.
The body shapes of fish that live at the bottom and in the upper layers of water are also different. For example, bottom fish (flounder, catfish, burbot, goby) have a flattened body, allowing them to rest on the ground with a large surface.
Sometimes fish adapt to passive movement. The leaf-shaped shape of eel larvae facilitates their transfer by currents from eel spawning sites located off the coast of Central America to permanent habitats in European water bodies.
In cases where fish hardly move, part of their body, together with the tail, turns into an attachment organ (seahorse).
The nature of nutrition also has a known influence on body shape; for example, in predatory fish that catch up with prey, the body is usually more slender than in fish that feed 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. Recent studies by physicists and ichthyologists have proven that the forward movement of fish is carried out mainly by wave-like 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 abdominal fins make it easier for the fish to move vertically and help to turn in the 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 lifestyle of the fish. Fish that swim in mid-water have large gill slits, and the gill filaments are constantly washed by fresh water rich in oxygen. In bottom fish - eel, flounder - the gill slits are small (otherwise they may become clogged with silt) with devices for forced circulation of water.
Fish that live in oxygen-poor water have additional respiratory organs. When there is a lack of oxygen in the water, crucian carp and some other fish swallow atmospheric air and use it to enrich the water with oxygen.
Tench, catfish and eel have additional cutaneous respiration. The swim bladder is involved in the respiratory functions of the perch, while the intestines of the loach are involved. Some warm-water fish are endowed with organs that allow them to breathe directly with atmospheric air. In some fish it is a special labyrinth apparatus, in others it is a swim bladder that has turned into a respiratory organ.
In accordance with the structure of the respiratory organs, fish have different attitudes towards the amount of oxygen dissolved in water. Some fish need a very high content of it in water - salmon, whitefish, trout, pike perch; others are less demanding - roach, perch, pike; Still others are satisfied with a completely insignificant amount of oxygen - crucian carp, tench. There is, as it were, a certain threshold for the oxygen content in water for each species of fish, below which individuals of a given species become lethargic, almost do not move, feed poorly and ultimately die.
Oxygen enters water from the atmosphere and is released by aquatic plants, the latter, on the one hand, releasing it under the influence of light, and on the other, absorbing it in the dark and expending it during decay. Therefore, “the positive role of plants in the oxygen regime is noticeable only during the period of their growth, that is, in the summer, and, moreover, during the day.
From the 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 the air, and the mixing of the different layers of water. The lower the temperature, the larger the water surface and the more intense the mixing, the better oxygen dissolves in water. Consequently, in summer, lower temperatures and strong winds help improve the well-being of fish, especially in reservoirs with insufficient oxygen. After rain, fish activity also increases and the bite becomes more active. Oxygen-saturated raindrops increase the total oxygen content in the reservoir.
Oxygen slowly penetrates from one water layer to another, and there is always more of it in the surface layers than near the bottom. This is one of the reasons for the weak development of life and the lack of accumulation of fish in the summer at depths, especially in stagnant reservoirs.
Lakes have 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 deep water that is poorly saturated with oxygen. Thus, near the quiet shore, a zone poorer in oxygen content is created, and the fish, all other things being equal, prefers to stay near the surf shore. 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 reservoirs in winter, when ice cover prevents air from accessing the water. This is especially noticeable in shallow, heavily overgrown reservoirs 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 outlet of spring waters, at the confluence of streams and rivers, are richer in oxygen. These places are usually chosen by fish for winter stopovers. In some lakes, especially in severe winters, the oxygen content in the water drops so much that mass death of fish occurs - the so-called kills.
In rivers, especially fast-flowing ones, there is no sharp natural lack of oxygen observed either in summer or winter. However, in rivers clogged with timber rafting waste and polluted by industrial wastewater, this deficiency can be so great that oxygen-demanding fish completely disappear.
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 high 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 a straight 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.
The world of oceans, seas, rivers and lakes is filled with many inhabitants. Fishes belong to the majority of inhabitants of the deep waters, but even in their huge family there are countless species. Almost all of them have common structural features, thanks to which they swim, or rather, move very quickly in their native element.
Muscles and fins of fish: engine, steering wheel and brakes
The bulk of a fish's body mass is made up of muscles. They connect to the spine and fins, ensuring their mobility through contractions. Thanks to their developed muscles, fish can masterfully control their own body, causing wave-like movements of the entire body or tail.
The fins are also connected to muscle fibers and, if necessary, can fold and unfold, changing the direction and speed of movement in the water. The main engine of fish is the caudal fin, a perfect oar created by nature, thanks to which sea animals move forward.
Paired pectoral and pelvic fins allow the fish to move up and down, while the dorsal and caudal fins enable them to stay upright and avoid turning around their own axis.
The subcaudal fins also serve as a brake for fish, and with the help of the ventral fins they can also rise to the surface. Fins can have different functional features that change depending on the situation and fish species.
In the marine family there are many exceptions to the general rules of movement. They are due to the diversity of animals and their role in the underwater world. It is for this reason that they are so interesting to watch.
Fish swimming methods
A classic is the swimming of marine species: sharks, herring, marlin and mackerel. Their bodies move rapidly, moving evenly from side to side. Trout make quick maneuvers during hunting, long swims upstream, and also when escaping from predators.
Tuna makes long sea crossings, thanks to slightly noticeable movements of the body, using its sickle-shaped tail as a rudder. And eels use only muscles and a tenacious tail to move; their fins have practically died out as unnecessary.
The seahorse moves in the water in an interesting way. Its dorsal fin oscillates with amazing speed. This fin is the only means for them to carry out sea walks and search for food.
Watching fish swim, you can see how diverse and beautiful the underwater world is, with what imagination and prudence it was created by nature and given to man. Protecting this oasis and studying its features is a big and difficult task for many years to come.
To get food and escape from enemies, fish must move in 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.