The adaptability of fish to the habitat. Adaptation of fish to life in water in the external and internal structure, reproduction
The most important property of all organisms on earth is their amazing ability to adapt to environmental conditions. Without it, they could not exist in constantly changing living conditions, the change of which is sometimes quite abrupt. Fish are extremely interesting in this respect, because the adaptability to the environment of some species over an infinitely long period of time led to the appearance of the first terrestrial vertebrates. Many examples of their fitness can be seen in the aquarium.
Many millions of years ago, in the Devonian seas of the Paleozoic era, there lived amazing, long extinct (with few exceptions) cross-finned fish (Crossopterygii), to which amphibians, reptiles, birds and mammals owe their origin. The marshes in which these fish lived began to gradually dry up. Therefore, over time, they also added pulmonary respiration to the gill respiration they had until now. And the fish more and more readjusted themselves to breathe oxygen in the air. Quite often it happened that they were forced to crawl from dried up reservoirs to places where there was still at least a little water left. As a result, five-toed limbs developed from their dense fleshy fins over many millions of years.
In the end, some of them adapted to life on land, although they had not yet moved very far from the water in which their larvae developed. This is how the first ancient amphibians arose. Their origin from cross-finned fish is proved by the finds of fossil remains, which convincingly show the path of evolution of fish to terrestrial vertebrates and thus to humans.
This is the most convincing material evidence of the adaptability of organisms to changing environmental conditions that can only be imagined. Of course, this transformation continued for millions of years. In the aquarium we can observe many other kinds of adaptability, less significant than the ones just described, but faster and therefore more visual.
Fish are quantitatively the richest class of vertebrates. To date, more than 8000 species of fish have been described, many of which are known in aquariums. In our reservoirs, rivers, lakes, there are about sixty species of fish, most of which are economically valuable. About 300 species of freshwater fish live on the territory of Russia. Many of them are suitable for aquariums and can serve as a decoration either for their entire life, or, at least, while the fish are young. On our common fish, we can most easily observe how they adapt to changes in the environment.
If we place a young carp about 10 cm long in a 50x40 cm aquarium and a carp of the same size in a second aquarium 100 x 60 cm in size, then after a few months we can state that the carp in the larger aquarium has outperformed the growth of the other carp from the small aquarium. ... Both received the same amount of the same food and, however, did not grow equally. In the future, both fish will stop growing altogether.
Why is this happening?
Reason - pronounced adaptability to external environmental conditions... Although the appearance of the fish does not change in a smaller aquarium, its growth slows down significantly. The larger the aquarium that contains the fish, the larger it will become. Increased water pressure - either to a greater or lesser extent, mechanically, through latent stimulation of the senses - causes internal, physiological changes; they are expressed in a constant slowdown in growth, which finally stops altogether. Thus, in five aquariums of different sizes, we can have carps of the same age, but completely different in size.
If a fish, which has been kept in a small vessel for a long time and which has therefore decayed, is placed in a large pool or pond, then it will begin to catch up in its growth. If it does not catch up with everything, however, it can significantly increase in size and weight even in a short time.
Under the influence of different environmental conditions, fish are able to significantly change their appearance. This is how fishermen know that between fish of the same species, for example, between pikes or trout caught in rivers, dams and lakes, there is usually a large enough difference. The older the fish, the usually more striking these external morphological differences, which are caused by prolonged stay in different environments. A rapidly flowing stream of water in a riverbed or the quiet depths of a lake and a dam in the same degree, but in different ways, affect the shape of the body, always adapted to the environment in which this fish lives.
But human intervention can change the appearance of a fish so much that an uninitiated person sometimes hardly thinks that it is a fish of the same species. Take, for example, the well-known veil-tails. Skillful and patient Chinese, through a long and careful selection, bred a completely different fish from the goldfish, which in the shape of the body and tail differed significantly from the original form. The veil tail has a rather long, often hanging, thin and split in two caudal fin, similar to the most delicate veil. Its body is rounded. Many types of veil-tails have bulging and even upward-facing eyes. Some forms of veil-tails have strange outgrowths on the head in the form of small combs or caps. A very interesting phenomenon is the adaptive ability to change color. In the skin of fish, like in amphibians and reptiles, in the pigment cells, the so-called chromotophores, there are innumerable pigment grains. In the skin of fish from chromotophores, mainly black-brown melanophores predominate. Fish scales contain silvery guanine, which causes this very shine, which gives the aquatic world such a magical beauty. Due to the compression and stretching of the chromotophore, a change in the color of the entire animal or any part of its body can occur. These changes occur involuntarily with various excitements (fright, fight, spawning) or as a result of adaptation to a given situation. In the latter case, the perception of the situation acts as a reflexive change in color. Anyone who had the opportunity to see flounders lying on the sand with the left or right side of their flat body in a marine aquarium could observe how this amazing fish quickly changes its color as soon as it gets on a new substrate. The fish constantly "strives" to merge with the environment so that neither its enemies nor its victims notice it. Fish can adapt to water with different amounts of oxygen, to different water temperatures and, finally, to a lack of water. Excellent examples of such adaptability exist not only in preserved little altered ancient forms, such as, for example, in lungfish, but also in modern fish species.
First of all, about the adaptive ability of lungs. There are 3 families of these fish living in the world, which resemble giant lung salamanders: in Africa, South America and Australia. They live in small rivers and swamps, which dry up during drought, and at normal water levels are very silty and muddy. If there is little water and it contains a sufficiently large amount of oxygen, the fish breathe normally, that is, with gills, only then swallowing air, since, in addition to the gills themselves, they also have special pulmonary sacs. If the amount of oxygen in the water decreases or the water dries up, they breathe only with the help of lung sacs, crawl out of the swamp, burrow into silt and fall into summer hibernation, which lasts until the first relatively large rains.
Some fish, like our brook trout, require a relatively large amount of oxygen for a normal life. Therefore, they can only live in running water, the colder and faster the water flows, the better. But it was experimentally found that forms that were grown in an aquarium from an early age do not require running water; they should only have colder or slightly blown water. They adapted to a less favorable environment due to the fact that the surface of their gills increased, which made it possible to receive more oxygen.
Aquarium lovers are well aware of labyrinth fish. They are so named because of the extra organ through which they can swallow oxygen in the air. It is an essential adaptation to life in puddles, rice paddies and other places with poor, decaying water. In an aquarium with crystal clear water, these fish will take in air less often than in an aquarium with cloudy water.
Convincing evidence of how living organisms can adapt to the environment in which they live are viviparous fish, very often found in aquariums. There are many types of them, small and medium in size, variegated and less colorful. All of them have a common feature - they give birth to relatively developed fry that no longer have a yolk sac and soon after birth live independently and hunt for small prey.
Already the act of mating of these fish differs significantly from spawning, because males fertilize mature eggs directly in the body of females. The latter, after a few weeks, discard the fry, which immediately swim away.
These fish live in Central and South America, often in shallow bodies of water and puddles, where after the end of the rains the water level drops and the water almost or completely dries up. In such conditions, the laid eggs would die. The fish have already adapted to this so that they can be thrown out of the drying puddles with strong jumps. Jumping, in relation to the very size of their body, is greater than that of a salmon. Thus, they jump until they fall into the nearest body of water. Here the fertilized female gives birth to fry. At the same time, only that part of the offspring that was born in the most favorable and deep water bodies is preserved.
Stranger fish live in the estuaries of tropical Africa. Their adaptation has stepped so far forward that they not only crawl out of the water, but can also climb the roots of coastal trees. These are, for example, mud jumpers from the goby family (Gobiidae). Their eyes, resembling those of a frog, but even more prominent, are located on the top of the head, which gives them the opportunity to navigate well on land, where they watch for prey. In case of danger, these fish rush to the water, bending and stretching the body like caterpillars. Fish adapt to their habitat mainly by their individual body shape. This, on the one hand, is a protective device, on the other hand, it is due to the way of life of various species of fish. So, for example, carp and crucian carps, feeding mainly on the bottom of motionless or sedentary food, while not developing a high speed of movement, have a short and thick body. Fish that burrow into the ground have a long and narrow body, predatory fish have either a body strongly compressed from the sides, like a perch, or torpedo-like, like a pike, pike perch or trout. This body shape, which does not represent strong water resistance, allows the fish to instantly attack prey. The overwhelming majority of fish have a streamlined body, well dissecting water.
Some fish have adapted due to their way of life to very special conditions so much that they even have little resemblance to fish at all. So, for example, seahorses have a prehensile tail instead of a tail fin, with the help of which they are fixed on algae and corals. They move forward not in the usual way, but thanks to the undulating movement of the dorsal fin. Seahorses are so similar to their environment that predators hardly notice them. They have excellent protective coloration, green or brown, and most species have long, fluttering processes on their bodies, very similar to algae.
In tropical and subtropical seas, there are fish that, fleeing from pursuers, jump out of the water and, thanks to the wide, membranous pectoral fins, glide many meters above the surface. These are the very flying fish. To facilitate flight, they have an unusually large air bubble in the body cavity, which reduces the relative weight of the fish.
Tiny sprayers from the rivers of southwestern Asia and Australia are perfectly adapted to hunting flies and other flying insects, landing on plants and various objects protruding from the water. The sprinkler sticks to the surface of the water and, noticing prey, sprays from the mouth with a thin stream of water, knocking the insect to the surface of the water.
Several fish species from various systematically distant groups have developed the ability to spawn far from their habitat over time. These include, for example, salmon fish. Before the ice age, they inhabited the fresh waters of the northern seas basin - their original place of residence. Already after the glaciers melted, modern salmon species appeared. Some of them have adapted to life in the salt water of the sea. These fish, for example, the well-known common salmon, go to the rivers for spawning, into fresh water, from where they later return back to the sea. Salmon were caught in the same rivers where they were first seen during migration. This is an interesting analogy with the spring and fall migrations of birds following very specific flight paths. The eel behaves even more interestingly. This slippery, serpentine fish breeds in the depths of the Atlantic Ocean, probably as deep as 6,000 meters. In this cold, deep-sea desert, which is only occasionally illuminated by phosphorescent organisms, tiny, transparent, leaf-shaped eel larvae hatch from innumerable eggs; they live in the sea for three years before they develop into true little eels. And then countless juvenile eels begin their journey into fresh river water, where they live for an average of ten years. By this time, they grow up and accumulate fat reserves in order to again set off on a long journey into the depths of the Atlantic, from where they never return.
The eel is excellently adapted to life at the bottom of the reservoir. The structure of the body gives him a good opportunity to penetrate into the very thickness of the silt, and if there is a lack of food, crawl on dry land into a nearby reservoir. Another interesting thing is the change in its color and the shape of the eyes when moving to sea water. Blackheads that are dark at first acquire a silvery sheen on the way, and their eyes become significantly larger. An enlargement of the eyes is observed when approaching the mouths of rivers, where the water is more brackish. This phenomenon can be caused in adult eels in the aquarium by dissolving a little salt in the water.
Why do the eyes of eels enlarge when traveling to the ocean? This device makes it possible to capture every, even the smallest beam or reflection of light in the dark depths of the ocean.
Some fish are found in waters poor in plankton (crustaceans moving in the water column, for example daphnia, some mosquito larvae, etc.), or where there are few small living organisms at the bottom. In this case, the fish adapt to feeding on insects falling to the surface of the water, most often flies. A small fish, about 1 cm in length, Anableps tetrophthalmus from South America has adapted to catching flies from the surface of the water. In order to be able to freely move directly at the very surface of the water, it has a straight back, strongly elongated with one, like a pike, a fin very shifted back, and its eye is divided into two almost independent parts, upper and lower. The lower part is an ordinary fish eye, and the fish looks under water with it. The upper part protrudes quite significantly forward and rises above the very surface of the water. With its help, the fish, examining the smooth surface of the water, discovers fallen insects. Only some examples of the inexhaustible variety of types of adaptation of fish to the environment in which they live are given. Just like these inhabitants of the aquatic kingdom, other living organisms are able to adapt to varying degrees in order to survive in the interspecies struggle on our planet.
Fish are the oldest vertebrate chordates that inhabit exclusively aquatic habitats - both salty and fresh water bodies. Compared to air, water is a denser habitat.
In the external and internal structure, fish have adaptations for life in water:
1. The shape of the body is streamlined. The wedge-shaped head merges smoothly into the body, and the body into the tail.
2. The body is covered with scales. Each scale is immersed in the skin with its front end, and with its rear end it lies on the scale of the next row, like a tile. Thus, the scales are a protective cover that does not interfere with the movement of the fish. On the outside, the scales are covered with mucus, which reduces friction during movement and protects against fungal and bacterial diseases.
3. Fish have fins. Paired fins (pectoral and pelvic) and unpaired fins (dorsal, anal, caudal) provide stability and movement in the water.
4. A special outgrowth of the esophagus - the swim bladder - helps fish to stay in the water column. It is filled with air. By changing the volume of the swim bladder, the fish change their specific gravity (buoyancy), i.e. become lighter or heavier than water. As a result, they can be at different depths for a long time.
5. The respiratory organs in fish are the gills, which absorb oxygen from the water.
6. The senses are adapted to life in water. The eyes have a flat cornea and a ball-shaped lens - this allows the fish to see only closely spaced objects. The olfactory organs open outward with the nostrils. The sense of smell in fish is well developed, especially in predators. The organ of hearing consists only of the inner ear. Fish have a specific sense organ - the lateral line.
It has the appearance of tubules stretching along the entire body of the fish. Sensitive cells are located at the bottom of the tubules. The fish perceive all the movements of the water with the side line. Thanks to this, they react to the movement of objects around them, to a variety of obstacles, to the speed and direction of currents.
Thus, due to the peculiarities of the external and internal structure, fish are perfectly adapted to life in the water.
What factors contribute to the onset of diabetes? Expand measures to prevent this disease.
Diseases do not develop on their own. For their appearance, a combination of predisposing factors, the so-called risk factors, is required. Knowledge of the factors involved in the development of diabetes helps to recognize the disease in a timely manner, and in some cases even prevent it.
Risk factors for diabetes mellitus are divided into two groups: absolute and relative.
The group of absolute risk of diabetes mellitus includes factors associated with heredity. This is a genetic predisposition to diabetes, but it does not give a 100% prognosis and a guaranteed undesirable outcome of the development of events. For the development of the disease, a certain influence of circumstances, the environment, manifested in relative risk factors, is necessary.
Relative factors in the development of diabetes mellitus include obesity, metabolic disorders, and a number of concomitant diseases and conditions: atherosclerosis, coronary heart disease, hypertension, chronic pancreatitis, stress, neuropathies, strokes, heart attacks, varicose veins, vascular damage, edema, tumors , endocrine diseases, long-term use of glucocorticosteroids, old age, pregnancy with a fetus weighing more than 4 kg and many, many other diseases.
Diabetes - it is a condition characterized by an increase in blood sugar levels. The modern classification of diabetes mellitus, adopted by the World Health Organization (WHO), distinguishes several of its types: 1st, in which the production of insulin by b-cells of the pancreas is reduced; and the second type is the most common, in which the sensitivity of body tissues to insulin decreases, even with its normal production.
Symptoms: thirst, frequent urination, weakness, complaints of itching of the skin, weight change.
In the cold and dark depths of the oceans, the water pressure is so great that no land animal could withstand it. Despite this, there are creatures that have been able to adapt to such conditions.
A variety of biotopes can be found in the sea. In marine depths in the tropical zone, the water temperature reaches 1.5-5 ° C, in the polar regions it can drop below zero.
A wide variety of life forms are presented below the surface at a depth, where sunlight is still able to receive it provides the possibility of photosynthesis, and, therefore, gives life to plants, which are the initial element of the trophic chain in the sea.
There are incomparably more animals in tropical seas than in arctic waters. The deeper the species diversity becomes poorer, less light, colder water, and higher pressure. At a depth of two hundred to a thousand meters, there are about 1000 species of fish, and at a depth of one thousand to four thousand meters, there are already only one hundred and fifty species.
The belt of waters from three hundred to a thousand meters deep, where semi-darkness reigns, is called the mesopelagiallu. At a depth of more than a thousand meters, darkness is already falling, the waves of the water here are very weak, and the pressure reaches 1 ton of 265 kilograms per square centimeter. Deep-sea shrimps of the genus MoIOBiotiz, cuttlefish, sharks and other fish, as well as numerous invertebrates live at such a depth.
OR YOU KNOW THAT ...
The dive record belongs to the cartilaginous fish Basogigas, which was sighted at a depth of 7965 meters.
Most deep-sea invertebrates are black in color, while most deep-sea fish are brown or black. Thanks to this protective coloration, they absorb the bluish-green light of the deep waters.
Many deep sea fish have air-filled swim bladders. And until now, researchers do not understand how these animals withstand the enormous pressure of water.
Males of some species of deep-sea anglerfish attach with their mouths to the belly of larger females and grow to them. As a result, the man remains attached to the female for the rest of his life, feeds at her expense, and even the circulatory system becomes common. And the female, thanks to this, does not have to look for a male during the spawning period.
One eye of a deep-sea squid that lives near the British Isles is significantly larger than the other. With the help of a large eye, he is guided by depth, and he uses the second eye when he rises to the surface.
Eternal twilight reigns in the depths of the sea, but numerous inhabitants of these biotopes glow in different colors in the water. The glow helps them attract mate, prey, and scare off enemies. The glow of living organisms is called bioluminescence.
BIOLUMINESIENCE
Many species of animals that inhabit the dark depths of the sea can emit their own light. This phenomenon is called the visible glow of living organisms, or bioluminescence. It is caused by the enzyme luciferase, which catalyzes the oxidation of substances produced by the light-luciferin reaction. Animals can create this so-called "cold light" in two ways. Substances necessary for bioluminescence, found in their body or in the body of luminous bacteria. In the European anglerfish, light-emitting bacteria are contained in vesicles at the end of the dorsal fin that grows in front of the mouth. Bacteria need oxygen to glow. When the fish does not intend to emit light, it closes the blood vessels that lead to the place in the body where the bacteria are located. The scalpelus speckled fish (Phyrophyllus parebrais) carries billions of bacteria in special bags under the eyes; with the help of special leather folds, the fish completely or partially covers these bags, regulating the intensity of the emitted light. To enhance the glow, many crustaceans, fish and squid have special lenses or a layer of cells that reflect light. The inhabitants of the depths use bioluminescence in different ways. Deep-sea fish glow in different colors. For example, the photophores of ribsokirok emit greenish, and photophores of the Astronest - violet-blue.
SEARCH FOR PARTNER
Inhabitants of the deep sea resort to various methods of attracting a partner in the dark. Light, smell and sound play an important role in this. In order not to lose the female, males even use special techniques. The relationship between males and females is interesting. Better studied the life of the European anglerfish. Males of this species usually find a large female without problems. With the help of their large eyes, they notice its typical light signals. Having found a female, the male firmly attaches to her and grows to her body. From that time on, he leads an attached lifestyle, even feeds through the female's circulatory system. When the female anglerfish lays eggs, the male is always ready to fertilize it. Males of other deep-sea fish, for example, gonostomids, are also smaller than females, in some of them the sense of smell is well developed. Researchers believe that in this case, the female leaves behind a scent trail that the male finds. Sometimes males of the European anglerfish are also found by the smell of females. In water, sounds are carried over a long distance. That is why males of three-headed and toad-like fins move their fins in a special way and make a sound that should attract the attention of the female. Toad fish give out beeps, which are transmitted as "boop".
At this depth, there is no light, and no plants grow here. Animals that live in the depths of the sea can only hunt the same deep-sea inhabitants or feed on carrion and organic debris that decays. Many of them, such as sea cucumbers, starfish and bivalve molluscs, feed on microorganisms, which they filter out of the water. Cuttlefish usually prey on crustaceans.
Many species of deep-sea fish eat each other or hunt small prey for themselves. Fish that feed on molluscs and crustaceans must have strong teeth to crush the shells that protect the soft bodies of their prey. Many fish have a lure located directly in front of the mouth, it glows and attracts prey. By the way, if you are interested in an online store for animals. please contact.
The temperature of the water largely determines the intensity of the metabolic process in fish. Temperature changes in many; cases are a natural irritant that determines the onset of spawning, migration, etc. Other physical and chemical properties of water, such as salinity, saturation; oxygen, viscosity are also of great importance.
DENSITY, VISCOSITY, PRESSURE AND MOTION OF WATER.
FISH MOVEMENT METHODS
Fish live in an environment that is much denser and more viscous than air; this is associated with a number of features in their structure, functions, their organs and behavior.
Fish are adapted to move in stagnant and flowing water. Water movements, both translational and oscillatory, play a very significant role in the life of fish. Fish are adapted to move in water in different ways and at different speeds. Associated with this are the shape of the body, the structure of the fins, and some other features in the structure of fish.
By the shape of the body, fish can be divided into several types (Fig. 2):. ¦
- Torpedo - the best swimmers, inhabitants of the water column, This group includes mackerel, mullet, herring shark, salmon, etc.
- Stenose - close to the previous one, but the body is more elongated and the unpaired fins are pushed back. Good swimmers, inhabitants of the water column - garfish, іtsuka.
- Flattened from side to side - this type varies the most. Usually it is subdivided into: a) bream-like, b) moon-fish type and c) flounder type. In terms of habitat, fish "belonging to this type are also very diverse - from inhabitants of the water column (moon-fish) to bottom (bream) or bottom (flounder).:
- ; Let it be seen - the body. , strongly elongated and flattened fc laterally. Bad swimmer herring king - kegalecus. Trachypterus, etc. ... ... , '(
- They are spherical and - the body is almost spherical, the caudal fin is usually poorly developed - box bodies, some pinagoras, etc.,
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Rice. 2. Various types of fish body shape:
/ - arrow-shaped (garfish); 2 - torpedo (mackerel); 3 - laterally flattened, bream-like (common bream); 4 - type of fish-moon (moon-fish);
5 - type of flounder (river flounder); 6 - serpentine (eel); 7 - ribbon-like (herring king); 8 - spherical (box body) 9 - flat (slope)
- Flat - flattened dorsoventrally different slopes, anglerfish.
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Rice. 3. Modes of movement: at the top - eel; below - cod. A wave is seen going through the body of the fish (from Gray, 1933)
Atnia calva L. Flounders swim, making oscillatory movements with both dorsal and anal fins. In the skate, swimming is provided by the oscillatory movements of the greatly enlarged pectoral fins (Fig. 4).
Rice. 4. The movement of fish using fins: anal (electric eel) or pectoral (ray) (from Norman, 195 8)
The caudal fin mainly paralyzes the braking movement of the end of the body and weakens reverse currents. By the nature of the action, it is customary to divide the tails of fish into: 1) isobaths and isobaths, where the upper and lower lobes are of equal size; a similar type of tail is found in mackerel, tuna and many others; 2) e and Ibatic, in which the upper lobe is better developed than the lower; this tail makes it easier to move up; this kind of tail is typical for sharks and sturgeons; 3) hypobatic, when the lower tail lobe is more developed than the upper one and promotes downward movement; a hypobatic tail is found in flying fish, bream, and some others (Fig. 5).
Rice. 5. Different types of fish tails (from left to right): epibatic, isobatic, hypobatic
The main function of the rudders is performed in fish by the pectorals, as well as by the abdominal dyats. With the help of them, the rotation of the fish in the horizontal plane is partly carried out. The role of unpaired fins (dorsal and anal), if they do not have the function of translational movement, is reduced to helping the fish turn up and down and only partly to the role of stabilizing keels (Vasnetsov, 1941).
The ability to bend the body more or less is naturally associated with. its structure. Fish with a large number of vertebrae can bend the body more strongly than fish with a small number of vertebrae. The number of vertebrae in fish ranges from 16 in the moon-fish, to 400 in the belt-fish. Also fish with small scales can bend their body to a greater extent than large-scale fish.
To overcome water resistance, it is extremely important to minimize body friction against water. This is achieved by smoothening the surface as much as possible and lubricating it with appropriate friction-reducing agents. In all fish, as a rule, the skin has a large number of goblet glands, which secrete mucus that lubricates the surface of the body. The best swimmer Among the fish have a torpedo-shaped body.
The speeds of movement of fish are also related to the biological state of the fish, in particular, the maturity of the gonads. They also depend on the temperature of the water. Finally, the speed of movement of the fish can vary depending on whether the fish are moving in a school or alone. Some sharks, swordfish,
tuna. Blue shark - Carcharinus gtaucus L. - moves at a speed of about 10 m / s, tuna - Thunnus tynnus L. - at a speed of 20 m / s, salmon - Salmo salar L. - 5 m / s. The absolute speed of movement of a fish depends on its size. 'Therefore, to compare the speed of movement of different-sized fish, the speed coefficient is usually used, which is the quotient of dividing the absolute speed of movement
fish at the square root of its length
Very fast moving fish (sharks, tuna) have a speed coefficient of about 70. Fast moving fish (salmon,
Rice. 6. Scheme of movement of a flying fish during takeoff. Side and top view (from Shuleikin, 1953),
mackerel) have a coefficient of 30-60; moderately fast ("herring, cod, mullet) - from 20 to 30; not fast (for example, bream) - QX 10 to 20; slow. (sculpin, scoriens) - from 5 to 10 and very slow (moon-fish, ba ) - less than 5.
/ Good swimmers in flowing water are somewhat different in / shape / body from good swimmers in standing water, in particular / in cervians, the caudal stem is usually / much higher, and "shorter than in the latter. As an example, you can compare the shape of the caudal stem of trout, adapted to live in water with a fast current, and mackerel - an inhabitant of slow-moving and stagnant sea waters.
Swimming quickly., Overcoming rapids and rifts, the fish get tired. They cannot swim for a long time without rest. Under high stress in fish, lactic acid accumulates in the blood, which then disappears during rest. Sometimes fish, for example, when passing through fish passages, get so tired that, having passed them, they even die (Bisk, 1958, etc.). In connection with. therefore, when designing fish passages, it is necessary to provide in them appropriate places for fish rest.
Among the fish there are representatives who have adapted to a kind of flight through the air. The best thing is
the property is developed in flying fish - Exocoetidae; in fact, this is not a real flight, but soaring like a glider. In these fish, the pectoral fins are extremely strongly developed and perform the same function as the wings of an airplane or glider (Fig. 6). The main engine that gives the initial speed during flight is the tail and, first of all, its lower blade. Having jumped out to the surface of the water, the flying fish slides along the water surface for some time, leaving behind itself ring waves diverging to the sides. While the body of a flying fish is in the air, and only its tail remains in the water, it still continues to increase the speed of movement, the growth of which stops only after the body of the fish is completely detached from the surface of the water. A flying fish can stay in the air for about 10 seconds and fly a distance of over 100 f.
Flight in flying fish has developed; - as a protective device that allows the fish to escape from the pursuing predators - tuna, coriphene, swordfish, etc. Among the haracin fish there are representatives (genera Gasteropelecus, Carnegiella, Thoracocharax), adapted to active flapping flight (fig. 7). These are small fish up to 9-10 cm in length, inhabiting the fresh waters of South America. They can jump out of the water and fly by flapping elongated pectoral fins up to 3-5 m.Although in flying haradinids, the size of the pectoral fins is smaller than in flying fish of the Exocoetidae family, the pectoral muscles that set the pectoral fins in motion are much more developed. These muscles in haracin fishes, which have adapted to flapping flight, attach to the very strongly developed bones of the shoulder girdle, which form a kind of resemblance to the thoracic keel of birds. The weight of the muscles of the pectoral fins in flying haracinids reaches 25% of the body weight, while in flightless representatives of the closely related genus Tetragonopterus - only: 0.7%,
The density and viscosity of water, as you know, depends, first of all, on the content of salts and temperature in the water. With an increase in the amount of salts dissolved in water, its density increases. On the contrary, as the temperature rises (above + 4 ° C), the density and viscosity decrease, and the viscosity is much stronger than the density.
Living matter is usually heavier than water. Its specific gravity is 1.02-1.06. The specific gravity of fish of different species varies, according to A.P. Andriyashev (1944), for fish of the Black Sea from 1.01 to 1.09. Consequently, a fish, in order to stay in the water column, “must have some kind of special adaptations, which, as we will see below, can be quite diverse.
The main organ by which fish can regulate
The swim bladder is responsible for its specific gravity, and, consequently, its confinement to certain layers of water. Few fish living in the water column do not have a swim bladder. There is no swim bladder in sharks and some mackerel. These fish regulate their position in a particular layer of water only with the help of the movement of their fins.
Rice. 7. Characin fish Gasteropelecus, adapted to flapping flight:
1 - general view; 2 - a diagram of the structure of the shoulder girdle and the location of the fin:
a - cleithrum; b -, hupercoracoideum; c - hypocoracoibeum; r - pte * rigiophores; d - fin rays (from Sterba, 1959 and Grasse, 1958)
In fish with a swim bladder, such as, for example, horse mackerel - Trachurus, wrasses - Crenilabrus and Ctenolabrus, southern haddock - Odontogadus merlangus euxinus (Nordm.), Etc., the specific gravity is slightly less than in fish without a swim bladder. , namely; 1.012-1.021. In fish without a swim bladder [sea ruff-Scorpaena porcus L., stargazer-Uranoscopus scaber L., goby-Neogobius melano- stomus (Pall.) And N. "fluviatilis (Pall.), Etc.], the specific gravity ranges from 1, 06 to 1.09.
It is interesting to note the relationship between the specific gravity of fish and its mobility. Of the fish that do not have a swim bladder, more mobile fish have a lower specific gravity, such as, for example, the sultanka - Mullus barbatus (L.) - (on average 1.061), and the largest - bottom, burrowing, such as the stargazer, the specific gravity which averages 1.085. A similar pattern is observed in fish with a swim bladder. Naturally, the specific gravity of fish depends not only on the presence or absence of a swim bladder, but also on the fat content of the fish, the development of bone formations (the presence of a shell) of the IT. etc.
The specific gravity of fish changes as it grows, as well as throughout the year due to changes in its fatness and fat content. So, in the Pacific herring - Clupea harengus pallasi Val. - the specific gravity varies from 1.045 in November to 1.053 in February (Tester, 1940).
In most of the more ancient groups of fish (among teleosts - in almost all herring and cyprinids, as well as in liverworms, mnogopers, bony and cartilaginous ganoids), the swim bladder is connected to the intestine using a special duct - ductus pneumaticus. In the rest of the fish - perch-like, cod-like and other * teleosts, in the adult state, the connection between the swim bladder and the intestine is not preserved.
In some herring and anchovies, for example, ocean herring - Clupea harengus L., sprat - Sprattus sprattus (L.), anchovy - Engraulis encrasicholus (L.), the swim bladder has two holes. In addition to ductus pneumaticus, in the posterior part of the bladder there is also an external opening that opens directly behind the anal one (Svetovidov, 1950). This hole allows the fish to remove excess gas from the swim bladder in a short time during a quick dive or ascent from a depth to the surface. At the same time, in fish sinking to a depth, excess gas appears in the bubble under the influence of the water pressure on its body that increases as the fish sinks. In the case of a rise with a sharp decrease in the external pressure, the gas in the bubble tends to occupy the largest possible volume, and in connection with this, the fish is also often forced to remove it.
A flock of herring floating to the surface can often be detected by numerous air bubbles rising from the depths. In the Adriatic Sea off the coast of Albania (Vlora Bay, etc.), when catching sardines for light, Albanian fishermen unmistakably predict the imminent appearance of this fish from the depths by the appearance of gas bubbles emitted by it. Fishermen just say: "The foam has appeared, and now there will be a sardinka" (message from GD Polyakov).
The filling of the swim bladder with gas occurs in open-bubble fish and, apparently, in most fish with a closed bladder, not immediately after leaving the egg. While the hatched free embryos go through the resting stage, suspended from the stems of plants or lying on the bottom, they have no gas in the swim bladder. The filling of the swim bladder occurs due to the ingestion of gas from the outside. In many fish, the duct connecting the intestine with the bladder is absent in the adult state, but in their larvae it is, and it is through it that their swim bladder is filled with gas. This observation is confirmed by the following experiment. The larvae hatched from the eggs of perch fish in such a vessel, the surface of the water in which was separated from the bottom by a thin mesh impermeable to the larvae. Under natural conditions, the filling of the bubble with gas occurs in perch fish on the second or third day after leaving the eggs. In the experimental vessel, the fish were kept up to five to eight days of age, after which the barrier separating them from the water surface was removed. However, by this time, the connection between the swim bladder and the intestine was interrupted, and the bladder remained unfilled with gas. Thus, the initial filling of the swimbladder with gas occurs in the same way in both open-bladder and most fish with a closed swimbladder.
In zander, gas in the swim bladder appears when the fish reaches approximately 7.5 mm in length. If by this time the swim bladder remains not filled with gas, then the larvae with an already closed bladder, even having the opportunity to swallow gas bubbles, overwhelm their intestines, but the gas no longer enters the bladder and leaves them through the anus (Kryzhanovsky, Disler and Smirnova, 1953).
From the vascular system (for unknown reasons), gas cannot begin to evolve into the swim bladder until at least a little gas enters it from the outside.
Further regulation of the amount and composition of gas in the swim bladder in different fish is carried out in different ways. In fish with a closed swim bladder, after the initial filling with gas from the outside, further changes in the amount and composition of the gas occur through its release and absorption by the blood. Such fish have a bladder on the inner wall. red body - formation extremely densely penetrated by blood capillaries. So, in two red bodies located in the swim bladder of an eel, there are 88,000 venous and 116,000 arterial capillaries with a total length of 352 and 464 m That is, no more than a drop of average size. The red body varies in different fish from a small spot to a powerful gas-secreting gland, consisting of a cylindrical glandular epithelium. Sometimes the red body is also found in fish with ductus pneumaticus, but in such cases it is usually less developed than in fish with a closed bladder.
In terms of the composition of the gas in the swim bladder, both different species of fish and different individuals of the same species differ. So, tench usually contains about 8% oxygen, perch - 19-25%, pike * - about 19%, roach - 5-6%. Since mainly oxygen and carbon dioxide can penetrate from the circulatory system into the swim bladder, it is these gases that usually predominate in the filled bladder; nitrogen in this case is a very small percentage. In contrast, when gas is removed from the swim bladder through the circulatory system, the percentage of nitrogen in the bladder rises sharply. Typically, marine fish have more oxygen in their swim bladder than freshwater fish. Apparently, this is mainly due to the predominance of forms with a closed swim bladder among marine fish. The oxygen content in the swim bladder is especially high in secondary deep-sea fish.
І
The gas pressure in the swim bladder in fish is usually transmitted in one way or another to the auditory labyrinth (Fig. 8).
Rice. 8. Diagram of the connection of the swimbladder with the organ of hearing in fish (from Kyle and Ehrenbaum, 1926; Wunder, 1936 and Svetovidova, 1937):
1 - ocean herring Clupea harengus L. (herring); 2 carp Cyprinus carpio L. (carps); 3 * - in Physiculus japonicus Hilgu (cod-like)
So, in herring, cod and some other fish, the anterior part of the swim bladder has paired outgrowths, which reach the holes of the auditory capsules tightened by the membrane (in cod), or even enter them (in herring). In carps, the pressure of the swim bladder is transmitted to the labyrinth using the so-called Weberian apparatus - a row of bones connecting the swim bladder with the labyrinth.
The swim bladder serves not only to change the specific gravity of the fish, but it also plays the role of an organ that determines the magnitude of the external pressure. A number of fish, for example,
in most loaches - Cobitidae, leading a bottom lifestyle, the swim bladder is greatly reduced, and its function as an organ that perceives pressure changes is the main one. Fish can perceive even small changes in pressure; their behavior changes with changes in atmospheric pressure, for example, before a thunderstorm. In Japan, some fish are specially kept for this purpose in aquariums and the change in their behavior is judged on the upcoming change in the weather.
With the exception of some herring fish, the swim bladder-possessing pbt; s cannot quickly move from the surface layers to the depths and vice versa. In this regard, in most species that make rapid vertical movements (tuna, common mackerel, sharks), the swim bladder is either completely absent or reduced, and retention in the water column is carried out due to muscular movements.
The swim bladder is also reduced in many bottom fish, for example, in many gobies - Gobiidae, blend dogs - Blenniidae, loaches - Cobitidae and some others. Bladder reduction in bottom-dwelling fish is naturally associated with the need to "provide a greater specific body weight. In some closely related fish species, the swim bladder is developed to varying degrees. For example, among gobies, some leading a pelagic lifestyle (Aphya), it is present; in others, such as, for example, in Gobius niger Nordm., it is preserved only in pelagic larvae; in gobies whose larvae also lead a benthic lifestyle, for example, in Neogobius melanostomus (Pall.), the swim bladder is also reduced in larvae and in adults.
In deep-sea fish, due to life at great depths, the swim bladder often loses its connection with the intestines, since at tremendous pressures the gas would be squeezed out of the bladder. This is characteristic even of representatives of those groups, for example, Opistoproctus and Argentina from the herring order, in which species living near the surface have ductus pneumaticus. In other deep-sea fish, the swim bladder can be reduced altogether, as, for example, in some Stomiatoidei.
Adaptation to life at great depths causes other serious changes in fish that are not directly caused by water pressure. These peculiar adaptations are associated "with the lack of natural light at depths ^ (see p. 48), the peculiarities of nutrition (see p. 279), reproduction (see p. 103), etc.
By its origin, deep-sea fish are heterogeneous; they come from various orders, often far apart from each other. At the same time, the time of transition to deep
... Rice. 9. Deep sea fish:
1 - Cryptopsarus couesii (Q111.); (feet); 2-Nemichthys avocetta Jord et Gilb (acne-like); .3 - Ckauliodus sloani Bloch et Schn, (herring): 4 - Jpnops murrayi Gunth. (glowing anchovies); 5 - Gasrostomus batrdl Gill Reder. (acne-like); 6 -x4rgyropelecus ol / ersil (Cuv.) (Glowing anchovies); 7 - Pseudoliparis amblystomopsis Andr. (perches); 8 - Caelorhynchus carminatus (Good) (long-tailed); 9 - Ceratoscopelus maderensis (Lowe) (glowing anchovies)
aquatic life in different groups of these species is very different. We can divide all deep-sea fish into two groups: ancient or true deep-water and secondary deep-water. The first group includes species belonging to such families, and sometimes to suborders and orders, all representatives of which have adapted to Habitat in the depths. Adaptations to the deep-sea lifestyle in these "fish are very significant. Due to the fact that the living conditions in the water column at depths are almost the same throughout the world's oceans, fish belonging to the group of ancient deep-sea fish are often very widespread. (Andriyashev, 1953) This group includes anglers ¦-Ceratioidei, luminous anchovies - Scopeliformes, large-moths - Saccopharyngiformes, etc. (Fig. 9).
The second group - secondary deep-water fish, includes forms, the deep-water of which is historically later. Typically, the families to which the species in this group belong are mainly fish. distributed within the continental stage or in the pelagic zone. Adaptations to life at depths in secondary deep-sea fish are less specific than in representatives of the first group, and the area of distribution is much narrower; widespread among them are not. Secondary deep-sea fish usually belong to historically younger groups, mainly perch-like fish - Pegsiogteae. We find deep-sea representatives in the families Cottidae, Liparidae, Zoarcidae, Blenniidae, etc.
While in adult fish a decrease in specific gravity is provided mainly due to the swim bladder, in eggs and larvae of fish this is achieved in other ways (Fig. 10). In pelagic, that is, eggs developing in the water column in a floating state, a decrease in the specific gravity is achieved due to one or several fat droplets (many flounders), or due to the "flooding of the yolk sac (red mullet - Mullus), or by filling a large round yolk - perivtelline cavity [grass carp - Ctenopharyngodon idella (Val.)], or swelling of the shell [octopus gudgeon - Goblobotia pappenheimi (Kroy.)].
The percentage of water contained in pelagic eggs is much higher than that of bottom eggs. So, in the pelagic eggs of Mullus, water accounts for 94.7% of the live weight, in the bottom eggs of atherina lt; - Athedna hepsetus ¦ L. - water contains 72.7%, and in the goby - Neogobius melanostomus (Pall.) - only 62 ,5%.
Peculiar adaptations are also developed in the larvae of fish leading a pelagic lifestyle.
As you know, the larger the area of a body in relation to its volume and weight, the more resistance it has during immersion and, accordingly, the easier it is to stay in one or another layer of water. Adaptations of this kind in the form of various spines and outgrowths that increase the surface of the body and contribute to keeping it in the water column are broken in many pelagic animals, including
Rice. 10. Pelagic fish eggs (not scaled):
1 - anchovy Engraulus encrasichlus L .; 2 - Black Sea herring Caspialosa kessleri pontica (Eich); 3 - Erythroculter erythrop "erus (Bas.) (Carp); 4 - red mullet Mullus barbatus ponticus Essipov (perches); 5 - Chinese perch Siniperca chuatsi Bas. (Perches); 6 - Bothus (Rhomball) maeoticus flounders (Rhomball) maeoticus ; 7 snakehead Ophicephalus argus warpachowskii Berg (snakeheads) (after Kryzhanovsky, Smirnov and Soin, 1951 and Smirnov, 1953) *
in fish larvae (Fig. 11). For example, the pelagic larva of the bottom fish of the monkfish - Lophius piscatorius L. - has long outgrowths of the dorsal and pelvic fins, which help it to soar in the water column; similar changes in fins are observed in the Trachypterus larva. The larvae of the moon fish -. Mota mola L. - have huge thorns on the body and somewhat resemble the enlarged planktonic alga Ceratium.
In some pelagic fish larvae, an increase in their surface occurs through a strong flattening of the body, as, for example, in the larvae of the river eel, the body of which is much higher and flat than in adult individuals.
In the larvae of some fish, for example, red mullet, even after the embryo leaves the shell, a powerfully developed fat drop retains the role of a hydrostatic organ for a long time.
In other pelagic larvae, the role of the hydrostatic organ is played by the dorsal fin fold, which expands into a huge swollen cavity filled with fluid. This is observed, for example, in the larvae of the sea carp - Diplodus (Sargus) annularis L.
Life in flowing water in fish is associated with the development of a number of special devices. We observe an especially fast current in rivers, where sometimes the speed of water movement reaches the speed of a falling body. In rivers originating from the mountains, the speed of water movement is the main factor determining the distribution of animals, including fish, along the course of the stream.
Adaptation to life in the river on the current for different representatives of the ichthyofauna goes in different ways. According to the nature of the habitat in the fast stream and the associated adaptation, the Hindu researcher Hora (1930) divides all the fish inhabiting the fast streams into four groups:
^ 1. Small species living in stagnant places: in barrels, under waterfalls, in backwaters, etc. These fish are the least adapted to life in a fast stream by their structure. Representatives of this group are the fast-growing - Alburnoides bipunctatus (Bloch.), The lady's stocking - Danio rerio (Ham.), Etc.
2. Good swimmers with a strong roll body, can easily overcome fast currents. This includes many river species: salmon - Salmo salar L., marinkas - Schizothorax,
Rice. 12. Suction cups for attachment to the ground of river fish: somica - Glyptothorax (left) and, Garra from carps (right) (from Noga, 1933 and Annandab, 1919)
^ some as Asian (Barbus brachycephalus Kpssl., Barbus "tor, Ham.) and African (Barbus radcliffi Blgr.) species of barbel and many others.
^ .3. Small bottom fish, usually living between the stones of the stream bottom and swimming from stone to stone. These fish, as a rule, have a spindle-shaped, slightly elongated shape.
These include many loaches - Nemachil "us, gudgeon" - Gobio and others.
4. Forms with special attachment organs (suckers; thorns), with the help of which they are attached to bottom objects (Fig. 12). Usually, fish belonging to this group have a flattened dorsoventrally body shape. A suction cup is formed either on the lip (Garra et al.) Or between
Rice. 13. Cross-section of various fishes of fast-flowing waters (upper row) and slow-flowing or standing waters (lower row). Left nappavo vveohu - th-.-
pectoral fins (Glyp-tothorax), or by fusion of the pelvic fins. This group includes Discognathichthys, many species of the Sisoridae family, and a kind of tropical family Homalopteridae, etc.
As the current slows down when moving from the upper to the lower reaches of the river, fish, unsuitable for overcoming high current velocities, rails, minnows, char, rockfishes begin to appear in the channel; down- In the fish that live in the waters
zu - mite, crucian carp, carp, roach, red - with a slow current, body
nope. Fish are taken of the same height more flattened, AND THEY are usually
’Not so good swimmers,
as inhabitants of fast rivers (Fig. 13). A gradual change in the shape of the fish body from the upper to the lower reaches of the river, associated with a gradual change in the speed of the current, is natural. In those places of the river where the current slows down, there are fish that are not adapted to life in a fast stream, in places with an extremely rapid movement of water, only forms adapted to overcoming the current are preserved; typical inhabitants of a fast stream - rheophiles, Van dem Born, taking advantage of the distribution of fish along the stream, divides the rivers of Western Europe into separate sections;
- the section of the trout — the mountainous part of the stream with a fast current and stony ground, is characterized by fishes with a lumpy body (trout, char, minnow, sculpin);
- barbel section - flat current, where the flow rate is still significant; there are already fish with a higher body, such as a barbel, a dace, etc.;?,
- the section of the bream is a slow flow, the ground is partly silt, and "partly sand, underwater vegetation appears in the channel, fish with a body flattened from the sides predominate, such as bream, roach, rudd, etc. v
usually occurs very gradually, but in general, the areas outlined by Borne are distinguished in most rivers with mountain food * rather clearly, and the patterns established by him for the rivers of Europe are preserved both in the rivers of America, Asia and Africa.
(^ (^ 4gt; Orms of the same species, living in flowing and stagnant water, differ in their adaptability to the current, For example, grayling - Thymallus arcticus (Pall.) - from Lake Baikal has a higher body and a longer tail stem, while representatives of the same species from the Angara are shorter and with short tails, which is characteristic of good swimmers. In addition, usually in mountain rivers, adults, larger and stronger individuals, stay upstream than young.If you move upstream of the river, then the average size of individuals of the same species, for example, comb-tailed and Tibetan loaches all increase, and the largest individuals are observed near the upper boundary of the species distribution (Turdakov, 1939).
UB River currents affect the fish organism not only mechanically, but also indirectly, through other factors. As a rule, reservoirs with a fast flow are characterized by * oversaturation of oxygen. Therefore, rheophilic fish are simultaneously oxyphilic, that is, oxygen-loving; and, conversely, fish inhabiting slowly flowing or stagnant waters are usually adapted to different oxygen conditions; the regime and better tolerate oxygen deficiency. ... -
The current, influencing the character of the stream's bottom, and thus the character of bottom life, naturally also influences the feeding of fish. So, in the upper reaches of rivers, where the soil forms motionless blocks. usually rich periphyton * can develop, which serves as the main food for many fish in this section of the river. Because of this, the fish of the upper reaches are characterized, as a rule, by a very long intestinal tract / adapted for the digestion of plant food, as well as the development of a horny cap on the lower lip. As you move down the river, the soils become shallower and, under the influence of the current, acquire mobility. Naturally, the rich bottom fauna cannot develop on moving soils, and the fish switch to feeding on fish or on food falling from the land. As the current slows down, siltation of the soil gradually begins, the development of bottom fauna, and herbivorous fish species with a long intestinal tract again appear in the channel.
33
The flow in the rivers influences not only the structure of the fish organism. First of all, the nature of reproduction of river fish changes. Many inhabitants of fast-flowing rivers
3 G. V. Nikolsky
have sticky caviar. Some species lay eggs by burying them in the sand. American catfish from the genus Plecostomus lay eggs in special caves, other genera (see reproduction) hatch eggs on their ventral side. The structure of the external genital organs also changes, some species develop less prolonged sperm motility, etc.
Thus, we see that the forms of adaptation of fish to the current in rivers are very diverse. In some cases, unexpected displacements of large masses of water, for example, silt silt, breakthroughs of dams in mountain lakes, can lead to mass death of ichthyofauna, as, for example, took place in Chitral (India) in 1929. The speed of the current sometimes serves as an isolating factor, "leading to the separation of the fauna of individual water bodies and contributing to its isolation. For example, the rapids and waterfalls between the large lakes of East Africa are not an obstacle for strong large fish, but impenetrable for small ones and lead to the isolation of faunas. thus separated sections of water bodies.:
"Naturally, the most complex and peculiar adaptations" to life on a fast current are developed in fish living in mountain rivers, where the speed of movement-water reaches the greatest value.
According to modern views, the fauna of mountain rivers in the temperate low latitudes of the northern hemisphere are relics of the Ice Age. (By the term "relict", we mean those animals and plants, the area of distribution of which is cut off in time or space from the main area of distribution of this faunistic or floristic complex.) "The fauna of mountain streams of tropical and, partially / temperate latitudes origin, but developed as a result of the gradual resettlement of “.organisms in. high-mountain reservoirs from the plains. - ¦¦: \
: For a number of groups, the ways of adaptation: to: life. In mountain streams can be traced quite clearly and can be restored (Fig. 14). --.that;
Both in rivers and in stagnant bodies of water, currents have a very strong effect on fish. But while in rivers the main "adaptations are developed to the direct mechanical: the effect of moving molasses, the influence of currents in; seas and lakes affects more indirectly - through changes caused by the current - in the distribution of other environmental factors (temperature, salinity, etc.). It is natural, of course, that adaptations to the direct mechanical effect of water movement are also developed in fish in stagnant water bodies. The mechanical effect of currents is primarily expressed in the transfer of fish, their larvae and eggs sometimes "Over great distances. So, for example, the larvae of agricultural
di - Clupea harengus L., hatched off the coast of northern Norway, are carried by the current far to the northeast. The distance from Lofoten, the herring spawning site, and to the Kola meridian, herring fry cover in about three months. The pelagic eggs of many fish are also over- -
Іurtertrnym, pavіyatym kernel.) /
/ n - Vi-
/ SshshShyim 9IURT0TI0YAL (RЯUІyІ RDR)
iyavit
Іurtotyanim
(meatsmy? гgt; im)
are carried by currents sometimes for very considerable distances. So, for example, eggs of flounders, laid off the coast of France, belong to the shores of Denmark, where fry emerge. The advancement of eel larvae from spawning grounds to the mouths of European rivers,
its part is timed to |
GlWOStlPHUH-
(sTouczm etc.)
spos ^ -
1І1IM from South to North. linea of catfish of the family "Yishin" pV
Minimum speeds are related to two main factors
cheniya nya kotooye reagents mountain streams .; On the diagram, it can be seen
the reaction to which the species has become less rheophilic
fish, apparently, of the order of 2- (dz Noga, G930).
10 cm / sec. Hamsa - - Engraulis "¦¦ ¦
encrasichalus L. - begins re- 1
aggravate the flow at a speed of 5 cm / sec, but for many species these threshold reactions have not been established. -
The organ that perceives the movement of water is the cells of the lateral line, in the simplest form in sharks it is. a series of sensory cells located in the epidermis. In the process of evolution (for example, in a chimera), these cells are immersed in a canal, which is gradually closed (in teleost fishes) and is connected by the environment only by means of tubes that pierce the scales and form a lateral line, which is far from the same in different fish. The organs of the lateral line "nervus facialis and n. Vagus innervate. In herring canals of the lateral line, only the head is present; in some other fish, the lateral line is incomplete (for example, in the top and some minnows). With the help of the lateral line organs, the fish perceives movement" and water fluctuations. Moreover, in many marine fish "the lateral line serves mainly for sensing the oscillatory movements of the water, and in river fish it allows one to orient oneself to the current (Disler, 1955, 1960).
The indirect influence of currents on fish, mainly through changes in the regime of waters, has a much greater effect than the direct one. Cold currents running from north to south allow Arctic forms to penetrate far into the temperate region. So, for example, the cold Labrador Current pushes the distribution of a number of warm-water forms far to the south, which along the coast of Europe, where the warm Gulf Stream is strongly affected, move far to the north. In the Barents Sea, the distribution of certain highly arctic species of the Zoarciaae family is confined to areas of cold water located between streams of warm currents. In the branches of this current, warmer-water fish, such as mackerel and others, are kept.
GTsdenias can radically change the chemical regime of the "reservoir and, in particular, affect its salinity, introducing more saline or fresh water. Thus, the Gulf Stream brings saltier water into the Barents Sea, and more saline-water organisms are confined to its streams. formed by fresh waters carried out by Siberian rivers, whitefish and Siberian sturgeon are largely confined in their distribution.At the junction of cold and warm currents, a zone of very high productivity is usually formed, since in such areas there is a massive dying off of invertebrates and plankton plants, giving a huge the production of organic matter, which allows a few eurythermal forms to develop in mass quantities.Examples of this kind of junction of cold and warm waters are quite common, for example, near the western coast of South America near Chile, on the Newfoundland banks, etc.
Rotational currents of water play a significant role in the life of fish. The direct mechanical effect of this factor is rarely observed. Usually, the effect of vertical circulation causes mixing of the lower and upper layers of the water, and thereby equalization of the distribution of temperature, salinity and other factors, which, in turn, creates favorable conditions for vertical migrations of fish. So, for example, in the Aral Sea, the vobla far from the coast in spring and autumn rises at night after the beggar into the surface layers in the daytime sinks into the bottom. In summer, when a pronounced stratification is established, the vobla is kept in the bottom layers all the time, -
Oscillatory movements of water also play an important role in the life of the fish. The main form of oscillatory movements of water, which is of the greatest importance in the life of fish, is excitement. Excitements have various effects on fish, both direct, mechanical and indirect, and are associated with the development of various adaptations. During strong waves in the sea, pelagic fish usually sink into deeper layers of water, where they do not feel the excitement. Excitement in coastal areas, where the force of wave impact reaches up to one and a half tons, has a particularly strong effect on fish.
living in the coastal zone, special devices are characteristic that protect them, as well as their eggs, from the influence of the surf. Most coastal fish are capable of *
per 1 m2. For fish / livestock /
hold in place in
surf time In against - Rice - 15 - Changed in a suction cup abdominal. ... l l "fins of marine fish:
BUT THEY would be on the left - Neogobius goby; on the right - the thorns are broken O stones. So, Pinagora Eumicrotremus (from Berg, 1949 and, for example, typical obi- Perm "nova, 1936)
tators of coastal waters - various gobies Gobiidae, have pelvic fins, modified into a suction cup, with the help of which fish are held on stones; a somewhat different nature of the suckers is found in the Cyclopteridae (Fig. 15).
At the Excitement not only directly mechanically affect the fish, but also have a large indirect effect on them, contributing to the mixing of water and submersion to the depth of the layer of the temperature jump. So, for example, in the last pre-war years, due to a decrease in the level of the Caspian Sea, as a result of an increase in the mixing zone, the upper boundary of the bottom layer, where the accumulation of nutrients occurs, also decreased. Thus, part of the nutrients entered the cycle of organic matter in the reservoir, causing an increase in the amount of plankton, and thus, the food base for the Caspian planktivorous fish. Thus, off the coast of North America and in the northern part of Okhotsk lor, the difference in high and low tide levels reaches more than 15 m. times a day, huge masses of water rush, they have special adaptations for life in small puddles the eggs remaining after low tide. All inhabitants of the intertidal zone (littoral) have a dorsoventrally flattened, serpentine, or valcate body shape. Tall-bodied fish, except for flounders lying on their sides, are not found in the littoral zone. So, in Murman, usually in the littoral zone there are eelpouts - Zoarces viuiparus L. and butterflies - Pholis gunnelus L. - species with an elongated body shape, as well as large-headed sculpins, mainly Myoxocephalus scorpius L.
Peculiar changes occur in tidal fish in breeding biology. Many of the fish in particular; podkamenniks, at the time of spawning, depart from the littoral zone. Some species acquire the ability of live birth, such as the eelpout, whose eggs undergo an incubation period in the mother's body. Pinagor usually lays its eggs below the low tide level, and in those cases when the caviar dries up, sprinkles it with water from the mouth, splashing its tail on it. What is the most curious adaptation to intertidal breeding in American fish? ki Leuresthes tenuis (Ayres), which spawns during syzygy tides in that part of the tidal zone that is not covered by quadrature tides, so that eggs develop outside the water in a humid atmosphere. The incubation period lasts until the next syzygy, when the fry emerge from the eggs and go into the water. Similar adaptations to breeding in the littoral zone are observed in some Galaxiiformes. Tidal currents, as well as vertical circulation, also have an indirect effect on fish, mixing bottom sediments and thus causing better assimilation of their organic matter, and thereby increasing the productivity of the reservoir.
The influence of such a form of water movement as tornadoes stands somewhat apart. Capturing huge masses of water from the sea or inland water bodies, tornadoes carry it along with all animals, including fish, over considerable distances. In India, during the monsoons, fish showers quite often occur, when usually live fish fall to the ground along with the downpour. Sometimes these rains cover quite large areas. Similar fish showers occur in various parts of the world; they are described for Norway, Spain, India and several other places. The biological significance of fish rains is undoubtedly primarily expressed in promoting the dispersal of fish, and with the help of fish rains, obstacles can be overcome, under normal conditions for. irresistible fish.
Thus / as can be seen from the above, the forms of influence on the “fish movement!
Fish, less than any other group of vertebrates, are associated with a solid substrate as a support. Many species of fish never touch the bottom in their entire life, but a significant, perhaps most of the fish are in a lean or other connection with the bottom of the reservoir. Most often, the relationship between the soil and fish is not direct, but is carried out through food objects that are triturated to a certain type of substrate. For example, the confinement of bream in the Aral Sea, at a certain time of the year, to gray muddy soils is entirely explained by the high biomass of the benthos of this soil (the benthos serves as food for the wood goblin). But in a number of cases, there is a connection between fish and the nature of the soil, caused by the adaptation of the fish to a certain type of substrate. So, for example, burrowing fish are always confined in their distribution to soft soils; fish, which are confined in their distribution to stony grounds, often have a suction cup for attaching to bottom objects, etc. Many fish have developed a number of rather complex adaptations for crawling on the ground. Some fish, sometimes forced to move on land, also have a number of features in the structure of their limbs and tail, adapted to movement on a solid substrate. Finally, the color of fish is largely determined by the color and pattern of the substrate on which the fish is located. Not only adult fish, but bottom fish - demersal eggs (see below) and the larvae are also in a very close relationship with the ground of the reservoir, on which eggs are laid or in which the larvae are kept.
There are relatively few fish that spend a significant part of their life buried in the ground. Among cyclostomes, a significant part of the time is spent in the ground, for example, the larvae of lampreys - sandworms, which may not rise to its surface for several days. The Central European spike - Cobitis taenia L. spends considerable time in the ground, just like the sandworm, it can even feed by burying itself in the ground. But most fish species are buried in the ground only during danger or during the period of drying out of the reservoir.
Almost all of these fish have a "snakelike elongated body and a number of other adaptations! Associated with burying. For example, in the Indian fish Phisoodonbphis boro Ham., Which digs passages in liquid silt, the nostrils look like tubes and are located on the ventral side of the head (Noga, 1934). This device allows the fish to successfully make its moves with a pointed head, while its nostrils are not clogged with silt.
body, similar to those movements that the fish makes when swimming. Standing at an angle to the surface of the ground with its head down, the fish, as it were, is screwed into it.
Another group of burrowing fish has a flat body, such as flounders and rays. These fish do not usually bury that deep. In them, the process of burying occurs in a slightly different way: the fish, as it were, throw the soil over themselves and usually do not completely burrow, exposing their head and part of the body outside.
Fish burrowing into the ground are mainly inhabitants of shallow inland water bodies or coastal areas of the seas. We do not observe this adaptation in fish from deep parts of the sea and inland water bodies. Of the freshwater fish that have adapted to burrowing into the ground, one can point out the African representative of lungs - Protopterus, burrowing into the ground of a reservoir and falling into a kind of summer hibernation during a drought. Of the freshwater fish of temperate latitudes, one can name the loach - Misgurnus fossilis L., usually burrowing during the drying up of water bodies, the spike -: Cobitis taenia (L.), for which burying in the ground serves mainly as a means of protection.
Examples of burrowing marine fish include the gerbil, Ammodytes, which also buries itself in the sand, mainly to escape pursuit. Some gobies - Gobiidae - hide from danger in the shallow burrows they dug. Flounders and rays are also buried in the ground mainly to be less noticeable.
Some fish, buried in the ground, can exist for quite a long time in wet silt. In addition to the above noted lungfish, common carp can often live in the silt of dried up lakes for a very long time (up to a year or more). This was noted for Western Siberia, Northern Kazakhstan, and the south of the European part of the USSR. There are cases when carps were dug from the bottom of dried up lakes with a shovel (Rybkin, 1 * 958; Shn "itnikov, 1961; Goryunova, 1962).
Many fish, although they do not bury themselves, can penetrate relatively deep into the ground in search of food. Almost all benthivorous fish dig up the soil to a greater or lesser extent. The digging of soil by them is usually carried out by a stream of water released from the mouth opening and carrying small silt particles aside. Directly growing movements in benthic-eating fish are observed less frequently.
Very often, digging up soil in fish is associated with the construction of a nest. For example, some representatives of the Cichlidae family, in particular, Geophagus brasiliense (Quoy a. Gaimard), build nests in the form of a hole where eggs are laid. To protect themselves from enemies, many fish buried eggs in the ground, where they
is developing. Caviar developing in the ground has a number of specific adaptations and develops worse outside the ground (see below, p. 168). Leuresthes tenuis (Ayres.) Can be mentioned as an example of marine fish burying eggs, and among freshwater fish - most salmon, in which both eggs and free embryos develop in the early stages, being buried in pebbles, protected in this way from numerous enemies. In fish burying eggs in the ground, the incubation period is usually very long (from 10 to 100 days or more).
In many fish, the shell of the egg, getting into the water, becomes sticky, due to which the egg attaches to the substrate.
Fish that keep on solid ground, especially in the coastal zone or in a fast current, very often have different organs of attachment to the substrate (see page 32); or - in the form of a sucker formed by a modification of the lower lip, pectoral or pelvic fins, or in the form of spines and hooks, usually developing on the ossifications of the shoulder and abdominal girdles and fins, as well as the gill cover.
As we have already indicated above, the distribution of many fish is confined to certain grounds, and often closely related species of the same genus are found on different grounds. So, for example, the goby - Icelus spatula Gilb. et Burke - is confined in its distribution to stony-pebble soils, and a closely related species - Icelus spiniger Gilb. - to sandy and silty-sandy. The reasons for the confinement of fish to a certain type of soil, as mentioned above, can be very diverse. This is either a direct adaptation to a given type of soil (soft - for burrowing forms, hard - for those who attach, etc.), or, since a certain nature of the soil is associated with a certain regime of the reservoir, in many cases there is a connection in the distribution of fish with the ground through the hydrological regime. Finally, the third form of link between fish distribution and soil is a link through the distribution of food items.
In many fish that have adapted to crawling on the ground, there have been very significant changes in the structure of the limbs. The pectoral fin serves for support on the ground, for example, in the larvae of polypterus (Fig. 18, 3), some labyrinths, such as the Anabas creeper, trigla - Trigla, jumpers - Periophftialmidae and many footed Lophiiformes, for example , anglerfish - Lophius piscatorius L. and starfish - Halientea. In connection with adaptation to movement on the ground, the forelimbs in fish undergo rather strong changes (Fig. 16). The most significant changes occurred in the Lophiiformes, in their forelimb a number of features are observed, similar to similar formations in tetrapods. In most fish, the skin skeleton is highly developed, and the primary skeleton is strongly reduced, while in tetrapods, the opposite picture is observed. Lophius occupies an intermediate position in the structure of the limbs, his primary and skin skeletons are equally developed. The two radialia in Lophius bear a resemblance to the zeugopodium of tetrapods. The musculature of the limbs of tetrapods splits into proximal and distal, which is located in two groups
Rice. 16. Pectoral fins of fish resting on the ground:
I - multi-opera (Polypteri); 2 - sea cock (trigly) (Perclformes); 3- Ogco- cephaliis (Lophiiformes)
pami, and not a solid mass, thereby making it possible for pronation and supination. The same is observed in Lophius. However, the musculature of Lophius is homologous to the musculature of other teleost fishes, and all changes towards the limb of tetrapods are the result of adaptation to a similar function. Using his limbs as his legs, Lophius moves very well along the bottom. Lophius and Polypterus have many common features in the structure of the pectoral fins, but in the latter, the muscle movement from the surface of the fin to the margins is observed to an even lesser extent than in Lophius. We observe the same or similar direction of changes and the transformation of the forelimb from the organ of swimming into the organ of support in the jumper - Periophthalmus. The jumper lives in mangroves and spends a significant part of the time on land. On the shore, it chases ground insects that it feeds on. "This fish moves on land by jumping, which it makes with the help of its tail and pectoral fins.
The trigger has a peculiar device for crawling on the ground. The first three rays of its pectoral fin are separated and acquired mobility. With the help of these rays, the triglya crawls along the ground. They also serve as the organ of touch for the fish. In connection with the special function of the first three rays, some anatomical changes also occur; in particular, the muscles that set the free rays in motion are much more developed than all the others (Fig. 17).
Rice. 17. Musculature of the pectoral fin rays of the sea cock (trigly). The enlarged muscles of the free rays are visible (from Belling, 1912).
The representative of the labyrinthine - the creeper - Anabas, moving on land, uses the pectoral fins for movement, and also sometimes the gill covers.
In the life of fish, oh! "- not only the soil, but also the solid particles suspended in the water play an important role.
The clarity of the water is very important in the life of fish (see page 45). In small inland water bodies and coastal areas of the seas, the transparency of the water is largely determined by the admixture of suspended mineral particles.
Particles suspended in water affect fish in a variety of ways. Suspensions of flowing water have the strongest effect on fish, where the solids content often reaches up to 4% by volume. Here, first of all, the direct mechanical effect of mineral particles of various sizes carried in the water affects, from a few microns to 2-3 cm in diameter. In this regard, fish of muddy rivers develop a number of adaptations, such as a sharp decrease in the size of the eyes. Lack of eyes is characteristic of shovelnose sturgeons, loaches - Nemachilus and various catfish living in muddy waters. The reduction in the size of the eyes is explained by the need to reduce the unprotected surface, which can be damaged by the suspension carried by the flow. The small eyes of loaches are also associated with the fact that et and bottom fishes are guided by food mainly with the help of the sense of touch. In the process of individual development, their eyes relatively decrease with the growth of the fish and the appearance of antennae and the associated transition to bottom feeding (Lange, 1950).
The presence of a large amount of suspended matter in the water, naturally, should make it difficult for fish to breathe. Apparently, in this regard, in fish living in turbid waters, mucus secreted by the skin has the ability to very quickly precipitate particles suspended in water. This phenomenon has been studied in most detail for the American scaly - Lepidosiren, the coagulating properties of the mucus of which help it to live in the thin silt of the Chaco reservoirs. For Phisoodonophis boro Ham. it has also been found that its mucus is highly susceptible to suspension. Adding one or two drops of mucus secreted by the skin of the fish to 500 cubic meters. cm of turbid water causes sedimentation of the suspension in 20-30 seconds. Such a rapid settling leads to the fact that even in very turbid water the fish lives, as it were, surrounded by a case of clean water. The chemical reaction of the mucus itself, secreted by the skin, when it comes into contact with cloudy water, changes. So, it was found that the pH of mucus in contact with water drops sharply, falling from 7.5 to 5.0. Naturally, the coagulating property of mucus is important as a way to prevent the gills from clogging up with suspended particles. But despite the fact that fish living in turbid waters have a number of devices to protect them from the effects of suspended particles, nevertheless, if the amount of turbidity exceeds a certain value, the fish may die. In this case, death, apparently, occurs from suffocation as a result of clogging of the gills with sediments. So, there are cases when during heavy rains - forces, with an increase in the turbidity of streams dozens of times, there was a mass death of fish. A similar phenomenon has been reported in the mountainous regions of Afghanistan and India. At the same time, even fish so adapted to life in troubled water as the Turkestan catfish-Glyptosternum reticulatum Me Clel died. - and some others.
LIGHT, SOUND, OTHER VIBRATORY MOTION AND RADIANT ENERGY FORMS
Light and, to a lesser extent, other forms of radiant energy play a very important role in the life of fish. Of great importance in the life of fish are other vibrational movements with a lower frequency of vibrations, such as sounds, infra-, and, apparently, ultrasounds. Electric currents, both natural and emitted by fish, are of well-known importance for fish. With its senses, the fish is adapted to perceive all these influences.
j Light /
Lighting is very important, both direct and indirect, in the life of fish. In most fish, the organ of vision plays an essential role in orientation during movement, towards prey, a predator, other individuals of the same species in a school, towards stationary objects, etc.
Only a few fish have adapted to live in complete darkness in caves and in artesian waters, or in the very weak artificial light produced by animals at great depths. "
The structure of the fish - its organ of vision, the presence or absence of luminescence organs, the development of other senses, coloration, etc. is associated with the peculiarities of illumination. The behavior of the fish, in particular, the daily rhythm of its activity and many other aspects of life, is largely associated with illumination. Light has a definite effect on the course of metabolism in fish, on the maturation of reproductive products. Thus, for most fish, light is a necessary element of their environment.
Lighting conditions in water can be very different and depend, in addition to the intensity of illumination, on reflection, absorption and scattering of light and many other reasons. An essential factor determining the illumination of water is its transparency. The transparency of water in various reservoirs is extremely diverse, ranging from the muddy, coffee-colored rivers of India, China and Central Asia, where an object immersed in water becomes invisible as soon as it is covered with water, and ending with the transparent waters of the Sargasso Sea (transparency 66.5 m), the central part of the Pacific Ocean (59 m) and a number of other places where the white circle is the so-called Secchi disk becomes invisible to the eye only after diving to a depth of more than 50 m. the same depth, are very different, not to mention different depths, for, as is known, the degree of illumination decreases rapidly with depth. So, in the sea off the coast of England, 90% of the light is absorbed already at a depth of 8-9 M.
The fish perceives light through the eyes and light-sensitive kidneys. The specificity of lighting in water determines the specificity of the structure and function of the fish's eye. As the experiments of Beebe (1936) showed, the human eye can still distinguish traces of light under water at a depth of about 500 m. even after a 2-hour exposure, it does not show any changes. Thus, animals living from a depth of about 1,500 m and ending with the maximum depths of the world's oceans over 10,000 m are completely influenced by daylight and live in complete darkness, disturbed only by the light emanating from the glow organs of various deep-sea animals.
-Compared to humans and other terrestrial vertebrates, fish are more myopic; her eye has a significantly shorter focal length. Most fish clearly distinguish objects within about one meter, and the maximum visual range of fish, apparently, does not exceed fifteen meters. Morphologically, this is determined by the presence in fish of a more convex lens than in terrestrial vertebrates. "
The horizontal field of view of each eye in an adult fish reaches 160-170 ° (data for trout), that is, more than in humans (154 °), and the vertical field in fish is 150 ° (in humans - 134 °). However, this vision is monocular. The binocular field of view in trout is only 20-30 °, while in humans it is 120 ° (Baburina, 1955). The maximum visual acuity in fish (minnow) is achieved at 35 lux (in humans - at 300 lux), which is associated with the adaptation of the fish to a lower, compared to air, illumination in water. The quality of the fish's vision is also related to the size of its eyes.
Fish, whose eyes are adapted to vision in the air, have a flatter lens. In the American four-eyed fish 1- Anableps tetraphthalmus (L.), the upper part of the eye (lens, iris, cornea) is separated from the lower by a horizontal septum. In this case, the upper part of the lens has a flatter shape than the lower, adapted for vision in water. This fish, swimming near the surface, can simultaneously observe what is happening in the air and in the water.
In one of the tropical species of companion dogs, Dialotn- tnus fuscus Clark, the eye is divided across by a vertical septum, and the fish can see with the front of the eye outside the water, and with the back - in the water. Living in depressions in the dry zone, it often sits with the front of its head out of the water (Fig. 18). However, outside the water, fish can also see, which do not expose their eyes to the air.
Being underwater, the fish can see only those objects that are to the vertical of the eye at an angle of no more than 48.8 °. As can be seen from the above diagram (Fig. 19), the fish sees air objects as if through a round window. This window expands when it sinks and narrows when it rises to the surface, but the fish always sees at the same angle of 97.6 ° (Baburina, 1955).
Fish have special adaptations for vision in different light conditions. Retinal rods are adapted to
Rice. 18. Fish, whose eyes are adapted to sight both in water, * and in air. Above - the four-eyed fish Anableps tetraphthalmus L .;
on the right is the section of her eye. ’
Below is the four-eyed blend Dialommus fuscus Clark; "
a - axis of air vision; b - dark septum; в - axis of underwater vision;
d - lens (according to Schultz, 1948),?
When receiving weaker light and in daylight, they sink deeper between the pigment cells of the retina, "which block them from light rays. Cones, adapted to the perception of brighter light, approach the surface under strong illumination.
Since the upper and lower parts of the eye are illuminated differently in fish, the upper part of the eye perceives more rarefied light than the lower one. In this regard, the lower part of the retina of the eye of most fish contains more cones and fewer rods per unit area. -
Significant changes occur in the structures of the organ of vision during ontogenesis.
In juvenile fish consuming food from the upper layers of water, an area of increased sensitivity to light is formed in the lower part of the eye, while switching to feeding on benthos increases the sensitivity in the upper part of the eye, which perceives objects located below.
The intensity of light perceived by the organ of vision in fish is apparently not the same in different species. American
Horizon \ Cerek Stones \ k
* Window S
.Shoreline / "M
Rice. 19. Visual field of fish looking up through the calm water surface. Above - water surface and airspace seen from below. Below is the same diagram from the side. Rays falling on the surface of the water from above are refracted inside the "window" and fall into the fish's eye. Inside the angle of 97.6 °, the fish sees the surface space, outside this angle, it sees the image of objects at the bottom, reflected from the surface of the water (from Baburina, 1955)
Lepomis of the family, Centrarchidae, the eye still picks up light with an intensity of 10 ~ 5 lux. A similar power of illumination is observed in the most transparent water of the Sargasso Sea at a depth of 430 m from the surface. Lepomis is a freshwater fish living in relatively shallow water bodies. Therefore, it is very likely that deep-sea fish, especially those with a telescopic. sky organs of vision, are able to respond to much weaker lighting (Fig. 20).
In deep-sea fish, a number of adaptations are developed in connection with low illumination at depths. Many deep-sea fish have enormous eyes. For example, in Bathymacrops macrolepis Gelchrist from the Microstomidae family, the eye diameter is about 40% of the head length. In Polyipnus from the Sternoptychidae family, the eye diameter is 25-32% of the head length, and in Myctophium rissoi (Sosso) from the
Rice. 20. Organs of vision of some deep-sea fish, Left - Argyropelecus affinis Garm .; right - Myctophium rissoi (Sosso) (from Fowler, 1936)
family Myctophidae - even up to 50%. The shape of the pupil very often changes in deep-sea fish - it becomes oblong, and its ends go behind the lens, due to which, just as by a general increase in the size of the eye, its light-absorbing ability increases. Argyropelecus from the Sternoptychidae family has a special light in the eye.
Rice. 21. Larva of deep-sea fish I diacanthus (order Stomiatoidei) (from Fowler, 1936)
a lingering organ that maintains the retina in a state of constant irritation and thereby increases its sensitivity to light rays coming from outside. In many deep-sea fish, the eyes become telescopic, which increases their sensitivity and expands the field of view. The most curious changes in the organ of vision take place in the larva of the deep-sea fish Idiacanthus (Fig. 21). Her eyes are located on long stalks, which makes it possible to greatly increase the field of view. In adult fish, the stalk of the eyes is lost.
Along with the strong development of the organ of vision in some deep-sea fish, in others, as already noted, the organ of vision either decreases significantly (Benthosaurus, etc.), or disappears completely (Ipnops). Along with the reduction of the organ of vision, these fish usually develop various outgrowths on the body: the rays of paired and unpaired fins or antennae are greatly lengthened. All these outgrowths serve as organs of touch and to a certain extent compensate for the reduction of the organs of vision.
The development of the organs of vision in deep-sea fish living at depths where daylight does not penetrate is due to the fact that many animals of the depths have the ability to glow.
49
The glow in animals, inhabitants of the sea depths, is a very common phenomenon. About 45% of fish inhabiting depths over 300 m have luminescence organs. In the simplest form, the organs of luminescence are presented in deep-sea fish from the family Macruridae. Their cutaneous mucous glands contain a phosphorescent substance that emits a weak light, creating
4 G. V. Nikolsky
giving the impression that the whole fish is glowing. Most other deep-sea fish have special organs of luminescence, sometimes quite complexly arranged. The most complex organ of luminescence of fish consists of an underlying layer of pigment, then a reflector is located, above which there are luminous cells covered with a lens on top (Fig. 22). The location is light
5
Rice. 22. Luminous organ of Argyropelecus.
¦ a - reflector; b - glowing cells; c - lens; d - underlying layer (from Brian, 1906-1908)
organs in different fish species are very different so that in many cases it can serve as a systematic sign (Fig. 23).
Usually, the glow occurs as a result of contact
Rice. 23. Layout of luminous organs in schooling deep-sea fish Lampanyctes (from Andriyashev, 1939)
the secret of luminous cells with water, but in the Asgoroth fish. japonicum Giinth. the reduction is caused by microorganisms in the gland. "The intensity of the glow depends on a number of factors and varies even in the same fish. Especially, many fish glow intensively during the breeding season.
What is the biological significance of the glow of deep-sea fish,
It has not yet been fully elucidated, but, undoubtedly, the role of the luminous organs is different for different fish: In Ceratiidae, the luminous organ located at the end of the first ray of the dorsal fin apparently serves to lure prey. It is possible that the luminous organ at the end of the tail of Saccopharynx performs the same function. The luminous organs of Argyropelecus, Lampanyctes, Myctophium, Vinciguerria and many other fish located on the sides of the body allow them to find individuals of the same species in the dark at great depths. This appears to be of particular importance for fish in schools.
Cave fish live in complete darkness, not disturbed even by luminous organisms. According to how closely animals are connected with life in caves, it is customary to subdivide them into the following groups: 1) troglobionts - permanent inhabitants of caves; 2) troglophiles - the predominant inhabitants of caves, but found in other places,
- trogloxenes are widespread forms that also enter caves.
To compensate for the degenerating organ of vision in cave fish, they usually have very strongly developed lateral line organs, especially on the head, and organs of touch, such as, for example, the long whiskers of Brazilian cave catfish from the family Pimelodidae.
The fish inhabiting the caves are very diverse. At present, representatives of a number of groups of the carp order are known in the caves - Cypriniformes (Aulopyge, Paraphoxinus, Chondrostoma, American catfish, etc.), Cyprinodontiformes (Chologaster, Troglichthys, Amblyopsis), a number of goby species, etc.
Illumination conditions in water differ from those in air not only in intensity, but also in the degree of penetration of individual rays of the spectrum into the depth of water. As is known, the coefficient of absorption of rays with different wavelengths by water is far from the same. Red rays are most strongly absorbed by water. When passing through a layer of water of 1 m, 25% of red is absorbed *
rays and only 3% purple. However, even violet rays at depths over 100 m become almost indistinguishable. Consequently, at the depths of the fish, colors are poorly distinguished.
The visible spectrum perceived by fish is slightly different from the spectrum perceived by terrestrial vertebrates. Different fish have differences associated with the nature of their habitat. Fish species living in the coastal zone and in the
Rice. 24. Cave fish (top to bottom) - Chologaster, Typhlichthys: Amblyopsis (Cvprinodontiformes) (from Jordan, 1925)
surface layers of water have a wider visible spectrum than fish living at great depths. The sculpin - Myoxocephalus scorpius (L.) is an inhabitant of shallow depths, perceives colors with a wavelength of 485 to 720 mmk, and the stellate ray holding at great depths is Raja radiata Donov. - from 460 to 620 mmk, haddock Melanogrammus aeglefinus L. - from 480 to 620 mmk (Protasov and Golubtsov, 1960). It should be noted that the reduction in visibility is primarily due to the long-wavelength part of the spectrum (Protasov, 1961).
A number of observations have proven that most fish species can distinguish colors. Apparently, only some cartilaginous fish (Chondrichthyes) and cartilaginous ganoids (Chondrostei) do not distinguish colors. The rest of the fish distinguish colors well, which has been proven, in particular, by many experiments using the conditioned reflex technique. For example, the gudgeon - Gobio gobio (L.) - was taught to take food from a cup of a certain color.
It is known that fish can change color and skin pattern depending on the color of the soil on which they are located. Moreover, if a fish accustomed to black soil and correspondingly changed its color was given a choice of a number of soils of different colors, then the fish usually chose the soil to which it was accustomed and the color of which corresponds to the color of its skin.
Particularly sharp changes in body color on various grounds are observed in flounders.
In this case, not only the tone changes, but also the pattern, depending on the nature of the soil on which the fish is located. What is the mechanism of this phenomenon has not yet been precisely clarified. It is only known that the color change occurs as a result of a corresponding irritation of the eye. Semner (Sumner, 1933), putting on transparent colored caps over the eyes of a fish, caused it to change color to match the color of the caps. The flounder, whose body is on the ground of one color, and the head - on the ground of a different color, changes the color of the body according to the background on which the head is located (Fig. 25). "
Naturally, the color of the fish body is closely related to the lighting conditions.
It is usually customary to distinguish the following main types of fish coloration, which are adaptation to certain habitat conditions.
Pelagic coloration ^ -blue or greenish dorsum and silvery sides and abdomen. This type of coloration is characteristic of fish living in the water column (herring, anchovies, bleak, etc.). The bluish back makes the fish hardly visible from above, and the silvery sides and abdomen are poorly visible from below against the background of the mirror surface.
Overgrown border - brownish, greenish or yellowish dorsum and usually transverse stripes or streaks on the sides. This coloration is common to fish in thickets or coral reefs. Sometimes these fish, especially in the tropical zone, can be very brightly colored.
Examples of fish with overgrown coloration are: common perch and pike - from freshwater forms; sea scorpion ruff, many wrasses and coral fish are from sea fish.
The bottom color is a dark back and sides, sometimes with darker streaks and a light abdomen (in flounders, the side facing the ground turns out to be light). Bottom fish living above the pebble bottom of rivers with clear water usually have black spots on the sides of the body, sometimes slightly elongated in the dorsal-abdominal direction, sometimes located in the form of a longitudinal strip (the so-called channel coloration). Such coloration is characteristic, for example, of juvenile salmon in the river period of life, juveniles of grayling, common minnow and other fish. This color makes the fish hardly noticeable against the background of pebble soil in clear flowing water. In bottom fish, stagnant waters usually do not have bright dark spots on the sides of the body, or they have a blurry outline.
The schooling coloration of fish is especially prominent. This coloration makes it easier for the flock to orientate one another (see p. 98 below). It manifests itself as either one or more spots on the sides of the body or on the dorsal fin, or as a dark strip along the body. An example is the coloration of the Amur minnow - Phoxinus lagovskii Dyb., Juvenile thorny bitter - Acanthorhodeus asmussi Dyb., Some herring, haddock, etc. (Fig. 26).
The coloration of deep-sea fish is very specific. Usually these fish are colored either dark, sometimes almost black or red. This is explained by the fact that even at relatively shallow depths, the red color appears black under water and is poorly visible to predators.
A somewhat different picture of coloration is observed in deep-sea fish that have luminescence organs on their bodies. These fish have a lot of guanine in the skin, which gives the body a silvery sheen (Argy-ropelecus, etc.).
As is well known, the color of fish does not remain unchanged during individual development. It changes during the transition of fish, in the process of development, from one habitat to another. For example, the color of juvenile salmon in the river has the character of the channel type, when they move into the sea, it is replaced by a pelagic color, and when the fish return to the river for reproduction, it again acquires a channel character. The color can change during the day; for example, some representatives of Characinoidei, (Nannostomus) have a gregarious color during the day - a black stripe along the body, and at night a transverse stripe appears, that is, the color becomes overgrown.
Rice. 26, Types of school coloration in fish (from top to bottom): Amur minnow - Phoxinus lagowsku Dyb .; thorny bittersweet (juveniles) - Acanthorhodeus asmussi Dyb .; haddock - Melanogrammus aeglefinus (L.) /
The so-called mating coloration in fish is often
protective device. The breeding coloration is absent in fish spawning at depths, and is usually poorly expressed in fish spawning at night.
Different types of fish react differently to light. Some are attracted by light: sprat Clupeonella delicatula (Norm.), Saury Cololabis saifa (Brev.), Etc. Some lt; fish, such as carp, avoid light. Fish are usually attracted to the light, which feed, orienting themselves with the help of the organ of vision / mainly the so-called "visual planktophages". The reaction to light also changes in fish in different biological states. Thus, females of anchovy sprat with flowing eggs are not attracted to the light, while those that have spawned or are in the pre-spawning state go to the light (Shubnikov, 1959). The nature of the reaction to light in many fish also changes in the process of individual development. Young salmon, minnow and some other fish hide from light under stones, which ensures their safety from enemies. In amidstorms, lamprey larvae (cyclostomes), whose tail bears light-sensitive cells, this feature is associated with life in the ground. Sandworms react to the illumination of the tail area with swimming movements, digging deeper into the ground.
... What are the reasons for the reaction of fish to light? There are several hypotheses on this issue (for a review, see Protasov, 1961). J. Loeb (1910) considers attracting fish to light as a forced, non-adaptive movement - as phototaxis. Most researchers view the response of fish to light as an adaptation. Franz (quoted by Protasov) believes that light has a signal value, in many cases serving as a signal of danger. SG Zusser (1953) believes that the reaction of fish to light is a food reflex.
There is no doubt that in all cases the fish reacts to light adaptively. In some cases, this may be a defensive reaction, when the fish avoids light, in other cases, the approach to light is associated with the extraction of food. Currently, a positive or negative reaction of fish to light is used in fishing (Borisov, 1955). Fish, attracted by the light to form clusters around the light source, are then caught either with netting tools or pumped out onto the deck by a pump. Fish that react negatively to light, such as the carp, are driven out of places that are inconvenient for fishing with the help of light, for example, from enclosed areas of a pond.
The importance of light in the life of fish is not limited only to the connection with vision. Illumination is also of great importance for the development of fish. In many species, the normal course of metabolism is disturbed if they are forced to develop in light conditions that are not characteristic of them (they are adapted to development in the light to mark in the dark, and vice versa). This is clearly shown by NN Disler (1953) on the example of the development of chum salmon in the world (see p. 193 below).
Light also affects the course of maturation of fish reproductive products. Experiments on the American palia, S * alvelinus foritinalis (Mitchill), showed that in experimental fish exposed to increased illumination, maturation occurs earlier than in controls exposed to normal light. However, in fish in alpine conditions, apparently, just like in some mammals under artificial illumination, light, after stimulating the enhanced development of the gonads, can cause a sharp drop in their activity. In this regard, the ancient alpine forms developed an intense coloration of the peritoneum, which protects the gonads from excessive exposure to light.
The dynamics of the intensity of illumination throughout the year largely determines the course of the sexual cycle in fish. The fact that in tropical fish reproduction occurs throughout the year, and in fish of temperate latitudes only at a certain time, is largely due to the intensity of insolation.
A peculiar protective device from light is observed in the larvae of many pelagic fish. So, in the larvae of herring of the genera Sprattus and Sardina, a black pigment develops above the neural tube, which protects the nervous system and underlying organs from excessive exposure to light. With resorption of the yolk bladder, the pigment above the neural tube in fry disappears. It is interesting that closely related species with bottom eggs and larvae kept in the bottom layers do not have such a pigment.
The sun's rays have a very significant effect on the course of metabolism in fish. Experiments carried out on mosquito fish (Gambusia affitiis Baird, et Gir.). showed that in mosquito fish, deprived of light, vitamin deficiency develops rather quickly, causing, first of all, the loss of the ability to reproduce.
Sound and other vibrations
As you know, the speed of sound propagation in water myoga is greater than in air. Otherwise, sound absorption in water also occurs.
Fish perceive both mechanical and infrasonic, sound and, apparently, ultrasonic vibrations. labyrinth, or rather its lower part - Sacculus and Lagena (the upper part serves as an organ of balance) In some species of fish, oscillations with a wavelength of 18 to 30 hertz, i.e., located on the border of infrasonic and sound waves, are perceived as lateral line organs, The differences in the nature of the perception of fluctuations in different species of fish are shown in Table 1.
In the perception of sound, the swim bladder also plays an essential role, apparently performing the role of a resonator. Since the propagation of sounds in water occurs faster and further, then their perception in water is easier. Sounds do not penetrate well from air1 into water. From water to air - a few1
Table 1
The nature of sound vibrations perceived by different fish
| | Frequency in hertz |
|
| Fish species | | |
| | from | BEFORE |
| Phoxinus phoxinus (L.) | 16 | 7000 |
| Leuciscus idus (L.) y. ¦ | 25 | 5524 |
| Carassius auratus (L.). | 25 | 3480 |
| Nemachilus barbatulus (L.) | 25 | 3480 |
| Amiurus nebulosus Le Sueur | 25 | 1300 |
| Anguilla anguilla (L.) | 36 | 650 . |
| Lebistes reticulatus Peters | 44 | 2068 |
| Corvina nigra C. V | 36 | 1024 |
| Diplodus annularis (L.) | 36 | 1250 |
| ¦Gobius niger L. | 44 | 800 |
| Periophthalmus koelreiteri (Pallas) | 44 | 651 |
better, since the sound pressure in water is much stronger than in air.
Fish can not only hear, many species of fish can make sounds themselves. The organs by which fish make sounds are different. In many fish, this organ is the swim bladder, which is equipped with special muscles. With the help of the swim bladder, the sounds of slabs (Sciaenidae), wrasses (Labridae), etc., are emitted. In catfish (Siluroidei), the organs that emit sound are the rays of the pectoral fins in combination with the bones of the shoulder girdle. In some fish, sounds are made with the help of the pharyngeal and jaw teeth (Tetrodontidae).
The nature of the sounds emitted by fish is very different: they resemble drum beats, croaking, grunting, whistling, and grunting. The sounds emitted by fishes are usually subdivided into "biological", that is, specially emitted by fishes and having an adaptive meaning, and "mechanical", emitted by fish when moving, feeding, digging up soil, etc. The latter usually have no adaptive meaning and on the contrary, they often unmask the fish (Malyukina and Protasov, 1960).
Among tropical fish, there are more species emitting "biological" sounds than among fish inhabiting water bodies of high latitudes. The adaptive meaning of the sounds emitted by fish is different. Often sounds are emitted by fish especially
intensively during reproduction and serve, apparently, to attract one sex to the other. This has been noted in croaker, catfish, and a number of other fish. These sounds can be so strong that fishermen can use them to find clusters of spawning fish. Sometimes you don't even need to submerge your head in water to detect these sounds.
In some croakeries, the sound is also important when fish in a feeding school come into contact. Thus, in the Beaufort region (Atlantic coast of the United States), the most intense sounding of croaker beetles falls in the dark from 21:00 to 02:00 and falls on the period of the most intensive feeding (Fish, 1954).
In some cases, the sound is intimidating. Killer whale catfish (Bagridae), which arrange their nests, apparently scare off enemies with creaking sounds, which they emit with the help of their fins. Special sounds are also emitted by the fish Opsanus tau, (L.) from the Batrachoididae family, when it guards its eggs.
The same type of fish can make different sounds, differing not only in strength, but also in frequency. So, Caranx crysos (Mitchrll) makes two types of sounds - croaking and rattling. These sounds differ in wavelength. " The sounds made by males and females are different in strength and frequency. This has been noted, for example, for the sea bass - Morone saxatilis Walb. from Serranidae, in which males emit stronger sounds and with a greater amplitude of frequencies (Fish, 1954). Young fish differ from the old ones in the nature of the sounds they make. The difference in the nature of sounds made by males and females of the same species is often associated with the corresponding differences in the structure of the sound-producing apparatus. So, in males haddock - Melanogrammus aeglefinus (L.) - the "tympanic muscles" of the swim bladder are much more developed than in females. Especially significant development of these muscles is achieved during spawning (Tempelman and. Hoder, 1958).
Some fish react very strongly to sounds. At the same time, some sounds of fish scare away, while others attract. When the engine knocks or the oar strikes the side of the boat, salmon often jumps out of the water, standing on holes in the rivers before spawning. The noise is caused by the Amur silver carp - Hypophthalmichthys molitrix (Val.) Jumping out of the water. On the reaction of fish to Sound, the use of sound when fishing is based. So, when fishing for mullet "matting", frightened by the sound, the fish jumps out. water and falls on special mats with raised edges on the surface, usually in the form of a semicircle. ¦ Having fallen on such a “mat”, the fish cannot jump back into the water. When fishing pelagic fish with a purse seine, sometimes a special bell is lowered into the net gate, including
and turning it off, which scares the fish away from the net gate during the purse (Tarasov, 1956).
Sounds are also used to attract fish to the place of fishing. From dyainih yaor.iavetents catfish catch "on a shred". Catfish are attracted to the place of fishing with peculiar gurgling sounds.
Powerful ultrasonic vibrations can kill fish (Elpiver, 1956).
By the sounds made by the fish, it is possible to detect their clusters. For example, Chinese fishermen detect spawning aggregations of the large yellow perch Pseudosciaena crocea (Rich.) By the sounds made by the fish. Having approached the supposed place of accumulation of fish, the foreman of the fishermen lowers a bamboo tube into the water and listens to the fish through it. In Japan, special radio beacons are installed, "tuned" to the sounds made by some commercial fish. When a school of fish of this species approaches the buoy, it begins to send appropriate signals, notifying fishermen about the appearance of fish.
It is possible that the sounds made by the fish are used by them as an echometric device. Locating by perceiving the sounds emitted is especially common, apparently, in deep-sea fish. In the Atlantic, near Porto Rico, it was found that biological sounds, apparently emitted by deep-sea fish, were then repeated in the form of a weak reflection from the bottom (Griffin, 1950). Protasov and Romanenko showed that the beluga makes rather strong sounds, sending which , she can detect objects that are from her at a distance of 15. and further.
Electric currents, electromagnetic vibrations
In natural waters, there are weak natural electric currents associated with both terrestrial magnetism and solar activity. Natural teluric currents have been established for the Barents and Black Seas, but they seem to be very comfortable in all significant water bodies. These currents are undoubtedly of great biological importance, although their role in biological processes in water bodies is still very poorly understood (Mironov, 1948).
Fish react subtly to electric currents. At the same time, many species can themselves not only produce electrical discharges, but, apparently, create an electromagnetic field around their body. Such a field, in particular, was established around the head area of the lamprey Petromyzon matinus (L.).
Fish can send and receive electrical discharges with their senses. The discharges produced by fish can be of two types: strong ^ serving for attack or defense (see below p. 110), or weak, having a signal
meaning. In the sea lamprey (cyclostomes), a voltage of 200-300 mV created near the front of the head is apparently used to detect (by changes in the generated field) objects approaching the head of the lamprey. It is likely that the "electrical organs" described by Stensio (P) 27 in cephalaspids had a similar function (Yuegekoper and. Sibakin 1956, 1957). Many electric eels produce mild rhythmic discharges. The number of discharges varied in the six studied species from 65 to 1000 centuries. The number of discharges also changes depending on the state of the fish. So, in a calm state Mormyrus kannume Bui. produces one impulse per second; being concerned, he sends up to 30 pulses per second. Floating gymnarch - Gymnarchus niloticus Cuv. - sends pulses with a frequency of 300 pulses per second.
Perception of electromagnetic waves in Mormyrus kannume Bui. are carried out using a number of receptors located at the base of the dorsal fin and innervated by the brain nerves extending from the hindbrain. In Mormyridae, impulses are sent by an electrical organ located on the caudal peduncle (Wright, 1958).
Different fish species have different susceptibility to electric current (Bodrova and Krayukhin, 1959). Of the studied freshwater fish, pike turned out to be the most sensitive, and tench and burbot were the least sensitive. Weak currents are perceived mainly by fish skin receptors. Stronger currents act directly on the nerve centers (Bodrova and Krayukhin, 1960).
By the nature of the fish's reaction to electric currents, three phases of action can be distinguished.
The first phase, when the fish, having fallen into the field of action of the current, shows anxiety and tries to leave it; in this case, the fish tends to take such a position in which the axis of its body would be parallel to the direction of the current. The fact that fish react to an electromagnetic field is now confirmed by the elaboration of conditioned reflexes in fish to it (Kholodov, 1958). When a fish enters the field of action of the current, its breathing rhythm becomes more frequent. Fish have species specificity in their reaction to electric currents. So the American catfish - Amiurus nebulosus Le Sueur - reacts to the current more strongly than the goldfish - Carassius auratus (L.). Apparently, fish with highly developed receptors in the skin react more sharply to toxins (Bodrova and Krayukhin, 1958). In the same species of fish, larger individuals react earlier to current than smaller ones.
The second phase of the action of the current on the fish is expressed in the fact that the fish turns its head towards the anode and swims towards it, very sensitively reacting to changes in the direction of the current, even very insignificant. Possibly, this property is related to the orientation of fish during migration to the sea to Teluric currents.
The third phase is galvanic anesthesia and the subsequent death of the fish. The mechanism of this action is associated with the formation of acetylcholine in the blood of fish, which acts as a drug. In this case, the respiration and cardiac activity of the fish are disturbed.
In fisheries, electric currents are used to catch fish, by directing its movement towards fishing gear or by causing shock to the fish. Electric currents are also used in electric barriers to prevent fish from entering the turbines of hydroelectric power stations, to irrigation canals, to direct the reef to the mouths of fish passages, etc. (Gyulbadamov, 1958; Nusenbaum, 1958).
X-rays and radioactivity
Roentgen beams have a strong negative effect on adult fish, as well as on eggs, embryos and larvae. As shown by the experiments of G.V. Samokhvalova (1935, 1938), carried out on Lebistes reticulatus, a dose of 4000 g is lethal for fish. Smaller doses of Lebistes reticulatus, when exposed to the reproductive gland, cause a decrease in feces and degeneration of the gland. Irradiation of young immature males causes underdevelopment of secondary sexual characteristics in them.
Upon penetration into water, "X-rays quickly lose their strength. As shown in fish, at a depth of 100 m, the strength of the X-rays is reduced by half (Folsom and Harley, 1957; Publ. 55I).
Radioactive radiation has a stronger effect on fish eggs and embryos than on adult organisms (Golovinskaya and Romashov, 1960).
The development of the atomic industry, as well as the testing of atomic hydrogen bombs, led to a significant increase in the radioactivity of air and water and the accumulation of radioactive elements in aquatic organisms. The main radioactive element that is important in the life of organisms is strontium 90 (Sr90). Strontium enters the fish organism mainly through the intestines (predominantly through the small intestines), as well as through the gills and skin (Danilchenko, 1958).
The bulk of strontium (50-65%) is concentrated in the bones, much less in the viscera (10-25%) and gills (8-25%), and very little in the muscles (2-8%). But strontium, which is deposited mainly in the bones, causes the appearance of radioactive ytrium-I90 in the muscles.
Fish accumulate radioactivity both directly from sea water and from other organisms that serve them as food.
The accumulation of radioactivity in young fish proceeds more rapidly than in adults, which is associated with a higher metabolic rate in the former.
More mobile fish (tuna, Cybiidae, etc.) more quickly remove radioactive strontium from their body than sedentary ones (for example, Tilapia), which is associated with different metabolic rates (Boroughs, Chipman, Rice, Publ, 551, 1957). In fish of the same species in a similar environment, as shown by the example of the long-eared perch - Lepomis, the amount of radioactive strontium in the bones can differ by more than five pa? (Krumholz, Goldberg, Boroughs, 1957 * Publ. 551). Moreover, the radioactivity of the fish can be many times higher than the radioactivity of the water in which it lives. So on Tilapia it was found that when the fish were kept in radioactive water, their radioactivity, in comparison with water, was the same two days later, and six times more after two months (Moiseev, 1958).
The accumulation of Sr9 ° in the bones of fish causes the development of the so-called Urov disease / associated with impaired calcium metabolism. Human consumption of radioactive fish is contraindicated. Since the half-life of strontium is very long (about 20 years), and it is firmly retained in the bone tissue, the fish remain infected for a long time. However, the fact that strontium is concentrated mainly in bones makes it possible to use in food fish fillets, deboned, after a relatively short aging, in storage (refrigerators), since ytrium concentrating in meat has a short half-life,
/water temperature /
In the life of fish, water temperature is of great importance.
Like other poikilrthermal ones, that is, with a variable body temperature, animal fish are more dependent on the temperature of the surrounding water than homothermic animals. At the same time, the main difference between them * lies in the quantitative aspect of the heat formation process.In cold-blooded vivrts, this process is much slower than in warm-blooded animals with a constant temperature teda. So, a carp weighing 105 g emits 10.2 kcal of heat per day, one kilogram, and a starling weighing 74 g - already 270 kcal.
In most fish, body temperature differs by only 0.5-1 ° from the temperature of the surrounding water, and only in tuna this difference can reach more than 10 ° C.
Changes in the temperature of the surrounding water are closely related to changes in the metabolic rate in fish. In many cases! temperature changes act as a signal factor, as a natural stimulus that determines the beginning of a particular process - spawning, migration, etc.
The rate of development of fish is also largely related to changes in temperature. Within a certain temperature range, a direct dependence of the rate of development on temperature changes is often observed.
Fish can live in a wide variety of temperatures. The highest temperature above + 52 ° C is carried by a fish from the Cyprinodontidae family - Cyprinodoti macularius Baird.- et Gir., Which lives in small hot springs in California. On the other hand, crucian carp - Carassius carassius (L.) - and dahlia, or black fish * Dallia pectoralis Bean. - withstands even freezing, however, provided that the body juices remain unfrozen. Saika - Boreogadus saida (Lep.) - leads an active lifestyle at a temperature of -2 °.
Along with the adaptation of fish to certain temperatures (high or low), the amplitude of temperature fluctuations at which the same species can live is very important for the possibility of their dispersal and life in different conditions. This temperature range is very different for different fish species. Some species can withstand fluctuations of several tens of degrees (for example, crucian carp, tench, etc.), while others are adapted to live with an amplitude of no more than 5-7 °. Typically, fish in the tropical and subtropical zone are more stenothermal than fish in temperate and high latitudes. Marine forms are also more stenothermal than freshwater ones.
If the total temperature range at which a species of fish can live can often be very large, then for each stage of development it usually turns out to be much smaller.
Fish react differently to temperature fluctuations and depending on their biological state. So, for example, salmon roe can develop at temperatures from 0 to 12 ° C, and adults easily tolerate fluctuations from negative temperatures to 18-20 ° C, and possibly even higher.
The carp successfully tolerates winter at temperatures ranging from negative to 20 ° C and above, but it can eat only at temperatures not lower than 8-10 ° C, and it reproduces, as a rule, at temperatures not lower than 15 ° C.
Usually fish are subdivided into stenothermic, that is, those adapted to a narrow amplitude of temperature fluctuations, and eurythermal - those. which can live within a significant temperature gradient.
Species specificity in fish is also associated with the optimal temperatures to which they are adapted. Fish of high latitudes have developed a type of metabolism that allows them to feed successfully at very low temperatures. But at the same time, in cold-water fish (burbot, taimen, whitefish) at high temperatures, activity sharply decreases and the intensity of feeding decreases. On the contrary, in fish of low latitudes, intensive exchange takes place only at high temperatures;
Within the range of temperatures optimal for a given type of fish, an increase in temperature usually leads to an increase in the intensity of food digestion. So, in a roach, as can be seen from the graph (Fig. 27), the rate of food digestion at
L
th
II "* J
O
zo zi
1-5 "5-S 10-15" 15-20 "20-26"
Temperature
5§.
I
S "S-
Fig. 27. Daily consumption (dotted line) and feed digestion rate (solid line) of roach Rutilus rutilus casplcus Jak. at different temperatures (according to Bokova, 1940)
15-20 ° C is three times more than at a temperature of 1-5 ° C. In connection with an increase in the rate of digestion, the intensity of feed consumption also increases.
Rice. 28., Change in oxygen concentration lethal for carp with temperature change (from Ivlev, 1938)
The digestibility of feed also changes with changes in temperature. So, in roach at 16 ° С, the digestibility of dry matter is 73.9%, and at 22 ° С -
81.8%. It is interesting that, at the same time, the digestibility of compounds, nitrogen in roach within these temperatures remains almost unchanged (Karzinkin, J952); in carp, that is, in fish that is more animal-eating than roach, with an increase in temperature, the digestibility of feed increases, both in general and in relation to nitrogen compounds.
Naturally, є changes in temperature are very
the gas exchange of fish also changes greatly. At the same time, the minimum oxygen concentration ¦, at which fish can live, often changes simultaneously. So for carp, at a temperature of 1 ° C, the minimum oxygen concentration is 0.8 mg / l, and at 30 ° C - already 1.3 mg / l (Fig. 28). Naturally, the number
65
5 G. v. NIKOLSKY
kysjofbda consumed by fish at - different temperatures is also associated with the state of the fish itself. "Г lt;" 1.
A change in temperature: influencing.; On „: a change in the metabolic rate of fish is also associated with a change in the toxic effects of various substances on its body. So, at 1 ° C the lethal concentration of CO2 for carp is 120 mg / l, and at 30 ° C this amount drops to 55-60 mg / l (Fig. 29).
504*
Rice. 29. Changes in the concentration of carbon dioxide, lethal for carp, due to temperature changes (from Ivlev, 1938)
With a significant decrease in temperature, fish can Fall into a state close to suspended animation, I will be in a hypothermic state for a more or less long time, even freezing into ice, such as crucian carp and black fish. ¦
Kai - experiments have shown that when the body of a fish freezes into the ice, its internal juices remain unfrozen and have a temperature of about - 0.2, - 0.3 ° C. Further cooling, provided that the fish is frozen in water, leads to a gradual decrease in temperature body of fish, freezing of cavity fluids and death. If the fish freezes outside the water, then usually its freezing is associated with preliminary hypothermia and a drop in body temperature for a short time even to -4.8 °, after which body fluids freeze and some temperature rise as a result of the release of latent heat of freezing. If the internal organs and gills freeze, then the death of the fish is inevitable.
The adaptability of fish to life at certain, often very narrow, temperature amplitudes is associated with the development in them of a rather subtle reaction to the temperature gradient.
... The minimum temperature gradient for which? fish react
; "Ch. (By Bull, 1936).:
Pholis gunnelus (L.) "J.. ...... 0.03 °
Zoarces viviparus (L.). ... ... ... , / ..... , 0.03 °
Myoxocepfiqlus scorpius (L.),. ... ... ... ... ... ... ... ... ... ... 0.05 °
Gadus morhua L.. ... ... ... :. ... ... ... i ¦. ... ... .. gt; ... ... ... 0.05 °
Odontogadus merlangus (L.). .... .4 . ... ... ... 0.03 "
Pollachius virens (L.) 0.06 °
Pleuronectes flesus L. ... ... 0.05 °.
Pteuroriectes platessa (L.). Y,. ... ... ... ... ... ... ... ... ... ... 0.06 °
Spinachia spinachia (L!) 0.05 °
Nerophis lumbriciformes Penn. ,. ... ... ... ... ... ... ... ... , 0.07 °
Since the fish is adapted to life at a certain
Tridene temperature in
Rice. ZO. Distribution:
1 - Ulcina olriki (Lutken) (Agonidae); 2 - Eumesogrammus praecisus (Kroyer) (Stichaeidae) in connection with the distribution of bottom temperatures (from Andriyashev, 1939)
temperature, it is natural that its distribution in the reservoir is usually associated with the temperature distribution. With seasonal and perennial changes in temperature, the kick is associated with a 40J change in the distribution of fish.
"The confinement of certain fish species to certain temperatures can be clearly judged by the reduced curve of the frequency of occurrence of certain fish species in connection with the temperature distribution (Fig. 30). As an example, we took representatives of the family -
Agonidae - Ulcina olriki (Lfltken) and Stichaeidae -
Eumesogrammus praecisus (Kroyer). As can be seen from Fig. 30, both of these species are confined in their distribution to completely definite different temperatures: Ulcina at a maximum occurs at a temperature of -.1.0-1.5 ° C, a * Eumesogrammus - at +1, = 2 ° C.
Knowing the confinement of fish to a certain temperature, it is often possible, when searching for their commercial concentrations, to be guided by the distribution of temperatures in the reservoir, f Long-term changes in water temperature (as, for example, in the North Atlantic due to the dynamics of the Atlantic Current) strongly affect the distribution of fish (Helland- Hansen and Nansen, 1909), During the warming years in the White Sea, there were cases of catching such relatively warm-water fish as mackerel - Scomber scombrus L., and in Kanin's nose - garfish * - Belone belone (L.). During periods of sweating, cod penetrates into the Kara Sea, and its commercial concentrations appear even off the coast of Greenland. ...
On the contrary, during periods of cold snaps, Arctic species descend to lower latitudes. For example, Arctic cod - Boreogadus saida (Lepechin) enters the White Sea in large quantities.
Sharp changes in water temperature sometimes cause mass death of fish. An example of this kind is the case of the chameleon-head - ¦ Lopholatilas chamaeleonticeps Goode et Bean (Fig. 31). Until 1879 this species was not known off the southern shores of New England.
In subsequent years, due to warming, it appeared
Rice. 31. Lopholatilus hamaeleonticeps Goode et Bean (chameleon-headed)
here in large numbers and became an object of fishing. As a result of a sharp cold snap in March 1882, a mass of individuals of this species died. They covered the surface of the sea with their corpses for miles. After this incident, for a long time, the chameleonheads completely disappeared from the indicated area and only in recent years reappeared in a rather significant number. ...
The death of - cold-water fish - trout, white fish - can also be caused by an increase in temperature, but usually the temperature affects the death not directly, but through a change in the oxygen regime, disrupting the breathing conditions.
Changes in fish distribution due to temperature changes have also occurred in previous geological eras. It has been established, for example, that in the reservoirs located on the site of the basin of the modern Irtysh, in the Miocene there were fish that were much warmer than those that inhabit the Ob basin now. Thus, the Neogene Irtysh fauna included representatives of the genera Chondrostoma, Alburnoides, Blicca, which are now not found in the Arctic Ocean basin in Siberia, but are distributed mainly in the Ponto-Aral-Kayopi province and, apparently, were. displaced from the basin - the Arctic Ocean as a result of climate change towards cooling (V. Lebedev, 1959). “.%
And at a later time, we find examples of changes in the distribution area and number of species under the * influence
changes in ambient temperature. Thus, the cooling caused by the onset of glaciers at the end of the Tertiary and early Quaternary periods led to the fact that representatives of the salmon family, confined to cold waters, were able to significantly advance southward to the Mediterranean Sea basin, including the rivers of Asia Minor and North Africa. At this time, salmon were much more abundant in the Black Sea, as indicated by the large number of bones of this fish in the remains of Paleolithic food.
In the postglacial period, climate fluctuations also led to changes in the composition of the ichthyofauna. So, for example, during the climatic optimum about 5,000 years ago, when the climate was somewhat warmer, the fish fauna of the White Sea basin contained up to 40% of warmer-water species such as asp - Aspius aspius (L.), rudd - Scardinius eryth- rophthalmus (L.) and blue bream - Abramis ballerus (L.) Now these species do not occur in the White Sea basin; they were undoubtedly driven out of here by the cold snap that took place even before the beginning of our era (Nikolsky, 1943).
Thus, the relationship between the distribution of certain species and temperature is very high. The attachment of representatives of each faunal complex to certain thermal conditions determines the frequent coincidence of boundaries between individual zoogeographic regions in the sea and certain isotherms. For example, the Chukotka moderate Arctic province is characterized by very low temperatures and, accordingly, the predominance of the Arctic fauna. Most of the boreal elements penetrate only into the eastern part of the Chukchi Sea together with the streams of the warm current. The fauna of the White Sea, separated into a special zoogeographic area, is much colder in composition than the fauna of the southern part of the Barents Sea located north of it.
The nature of distribution, migrations, spawning and feeding grounds for the same species in different parts of the area of its distribution may be different due to the distribution of temperature and other environmental factors. For example, in the Pacific cod Gadus morhua macrocephalus Til. - off the coast of the Korean Peninsula, breeding sites are located in the coastal zone, and in the Bering Sea at depths; the feeding grounds are reversed (Fig. 32).
The adaptive changes that occur in fish with temperature changes are also associated with some morphological restructuring. For example, in many fish, the adaptive response to changes in temperatures, and thus water density, is a change in the number of vertebrae in the tail region (with closed hemal arches), i.e., a change in hydrodynamic properties in connection with adaptation to movement in water. density.
Similar adaptations are observed in fish developing at different salinities, which is also associated with changes in density. It should be noted that the number of vertebrae changes with changes in temperature (or salinity) during the
February
200
№
Depth 6 m bering hole
Western
Kamchatka
Tatar Strait ~ 1
Southern part of 3 “Japanese muzzles,
b "°
August 100 200
Southern part of the ¦Japanese Sea
Rice. 32. Distribution of the Pacific cod Gadus morhua macrocephalus Til. in different parts of its distribution area due to temperature distribution; oblique shading - breeding sites (from Moiseev, 1960)
NS
Depth 6 m
Beringo
sea
Western
Kamchatka
Tatar
spill
tation of the body. If the impact of this kind takes place at later stages of development, then there are no changes in the number of metameres (Hubbs, 1922; Taning, 1944). A similar phenomenon was observed for a number of fish species (salmon, cyprinids, etc.). Similar changes occur in some fish species.
and in the number of rays in unpaired fins, which is also associated with adaptation to movement in water of various densities.
It is especially necessary to dwell on the values of ice in the Life of fish. The forms of the influence of ice on fish are very diverse] This is a direct temperature effect, since when Water freezes, the temperature rises, and when the ice melts, it decreases. But other forms of ice influence are much more important for fish. The ice cover is especially important as an insulator of water 6 tons of the atmosphere. During freeze-up, the influence of winds "on the water almost completely stops, the flow of oxygen from the air slows down greatly, etc. (see below). By isolating the water from the air, ice also makes it difficult for light to penetrate it. Finally, ice sometimes on fish and mechanical impact: There are cases when in the coastal strip the fish and caviar brought to the shore were crushed by the ice on the coast. Ice also plays a role in changing the chemical composition of water and the value of salinity: Salt composition / ice is different from the salt composition of sea water, and with massive ice formation, not only the salinity of the water changes, while increasing, but also the ratio of salts. Ice melting, on the contrary, causes a decrease in salinity and a change in the salt composition of the opposite character. "then .- / then‘
Living conditions in various areas of fresh water, especially in the sea, leave a sharp imprint on the fish living in these areas.
Fish can be divided into marine, anadromous, semi-anadromous, or estuarine fish, brackish water and freshwater fish. Already significant differences in salinity are important for the distribution of individual species. The same is true for the differences in the rest of the properties of water: temperature, lighting, depth, etc. Trout requires different water than barbel or carp; tench and crucian carp also keep in such bodies of water where perch cannot live because of too warm and muddy water; The asp requires clean, flowing water with fast ripples, and the pike can stay in stagnant water overgrown with grass. Our lakes, depending on the living conditions in them, can be distinguished as zander, bream, crucian, etc. Inside more or less large lakes and rivers, we can note different zones: coastal, open water and bottom, characterized by different fish. Fish from one zone can enter another zone, but in each zone one or another species composition prevails. The coastal zone is richest. The abundance of vegetation, hence food, makes this area favorable for many fish; here they feed, here they dash an acre. Distribution of fish by zones plays an important role in fisheries. For example, burbot (Lota lota) is a bottom fish, and it is caught from the bottom with venters, but not with flowing nets, which are used to catch asp, etc. Most whitefishes (Coregonus) feed on small planktonic organisms, mainly crustaceans. Therefore, their habitat depends on the movement of plankton. In winter they leave after the latter to the depth, in spring they rise to the surface. In Switzerland, biologists have indicated the places where planktonic crustaceans live in winter, and here the whitefish fishery arose after that; On Lake Baikal, omul (Coregonus migratorius) is caught with nets in winter at a depth of 400-600 m.
The delimitation of a zone in the sea is more pronounced. According to the living conditions that it provides for organisms, the sea can be divided into three zones: 1) littoral, or coastal; 2) pelagic, or open sea zone; 3) abyssal, or deep. The so-called sublittoral zone, which constitutes the transition from coastal to deep, already reveals all the signs of the latter. Their boundary is a depth of 360 m.The coastal zone starts from the coast and extends to a vertical plane that bounds an area deeper than 350 m.The open sea zone will be outward from this plane and up from another plane lying horizontally at a depth of 350 m The deep zone will be below from this last (Fig. 186).
Light is of great importance for all life. Since water weakly transmits the rays of the sun, conditions of existence unfavorable for life are created in the water at a certain depth. According to the intensity of illumination, there are, as indicated above, three light zones: euphotic, dysphotic and aphotic.
Free-swimming and near-bottom forms are closely intermixed near the coast. Here is the cradle of marine animals, from here clumsy bottom dwellers and nimble swimmers of the open sea arise. Thus, off the coast, we find a rather diverse mixture of types. But the living conditions on the open sea and at depths are very different, and the types of animals, in particular, fish, in these zones are very different from each other. All animals that live on the bottom of the sea, we call one name: benthos. These include crawling to the bottom, lying on the bottom, burrowing forms (mobile benthos) and sessile forms (sessile benthos: corals, sea anemones, tubular worms, etc.).
Those organisms that can swim freely are called pectons. The third group of organisms, devoid or almost deprived of the ability to move actively, clinging to algae or helplessly carried in the wind or currents, is called planktol. Among fish, we have forms belonging to all three groups of organisms.
Non-lagic fish are nekton and plankton. Organisms living in water independently of the bottom, not associated with it, are called non-lagic. This group includes organisms both living on the surface of the sea and in its deeper layers; organisms actively swimming (nekton), and organisms carried by the wind and currents (plankton). Deeply living pelagic animals are called bathinelagic.
The living conditions on the open sea are characterized primarily by the fact that there is no surf here, and the animals do not need to develop adaptations to keep them at the bottom. The predator has nowhere to hide here, trapping the prey, the latter has nowhere to hide from predators. Both must rely mainly on their own speed. Most of the fish on the open sea are therefore excellent swimmers. This is first; secondly, the color of sea water, blue in both transmitted and incident light, affects the color of pelagic organisms in general and fish in particular.
Adaptations of nekton fish to movement are different. We can distinguish several types of nekton fish.
In all of these types, the ability to swim quickly is achieved in different ways.
The type is spindle-shaped, or torpedo-shaped. The organ of movement is the tail section of the body. Examples of this type are: herring shark (Lamna cornubica), mackerel (Scomber scomber), salmon (Salmo salar), herring (Clupea harengus), cod (Gadus morrhua).
The type is ribbon-shaped. Movements occur with the help of serpentine movements of a long, ribbon-like body compressed from the sides. For the most part, they are inhabitants of rather great depths. Example: king herring, or belt fish (Regalecus banksii).
Arrow-shaped type. The body is elongated, the snout is pointed, strong unpaired fins are carried back and are located in the form of an arrow feather, making up one piece with the caudal fin. Example: common garfish (Belone belone).
Sail-shaped type. The snout is elongated, the unpaired fins and the general appearance are the same as in the previous one, the front dorsal fin is greatly enlarged and can serve as a sail. Example: sailboat (Histiophorus gladius, fig. 187). This also includes the swordfish (Xiphias gladius).
A fish is essentially an animal that actively swims. Therefore, there are no real planktonic forms among them. We can distinguish the following types of fish approaching plankton.
The type is needle-shaped. Active movements are weakened, performed with the help of rapid bends of the body or undulating movements of the dorsal and anal fins. Example: Pelagic needlefish (Syngnathus pelagicus) of the Sargasso Sea.
The type is compressed symmetrical. The body is tall. The dorsal and anal fins are opposite each other, high. Most of the pelvic fins are absent. Movement is very limited. Example: moonfish (Mola mola). This fish also lacks a caudal fin.
He does not make active movements, the muscles are largely atrophied.
The type is spherical. The body is spherical. The body can be inflated in some fish due to the ingestion of air. Example: hedgehog fish (Diodon) or deep-sea melanocetus (Melanocetus) (Fig. 188).
There are no true planktonic forms among adult fish. But they are found among planktonic eggs and larvae of planktonic fish. The body's ability to stay in water depends on a number of reasons. First of all, the specific gravity of water is important. The body keeps on water, according to Archimedes' law, if its specific gravity is not more than the specific gravity of water. If the specific gravity is greater, then the body sinks at a rate proportional to the difference in specific gravity. The sink rate, however, will not always be the same. (Small grains of sand sink more slowly than large stones of the same specific gravity.)
This phenomenon depends, on the one hand, on the so-called viscosity of water, or, internal friction, on the other, on what is called surface friction of bodies. The larger the surface of an object in comparison with its volume, the greater its surface resistance, and it sinks more slowly. The low specific gravity and high viscosity of the water resists immersion. As is known, copepods and radiolarians are excellent examples of such a change. We observe the same phenomenon in eggs and in fish larvae.
Pelagic eggs are mostly small. The eggs of many pelagic fish are equipped with filamentous outgrowths that prevent them from submerging, for example, eggs of the mackerel fishes (Scombresox) (Fig. 189). The larvae of some fish leading a pelagic lifestyle have a device for keeping on the surface of the water in the form of long filaments, outgrowths, etc. Such are the pelagic larvae of the deep-sea fish Trachypterus. In addition, the epithelium of these larvae is changed in a very peculiar way: its cells are almost devoid of protoplasm and are stretched to enormous sizes with liquid, which, of course, by reducing the specific gravity, also contributes to the retention of the larvae in the water.
Another condition affects the ability of organisms to stay on water: osmotic pressure, which depends on temperature and salinity. With a high salt content in the cell, the latter absorbs water, and, although it becomes heavier, its specific gravity decreases. Once in more salty water, the cell, on the contrary, decreases in volume and becomes heavier. The pelagic eggs of many fish contain up to 90% water. Chemical analysis has shown that in the eggs of many fish, the amount of water decreases with the development of the larva. As the water becomes depleted, the developing larvae sink deeper and, finally, sit on the bottom. The transparency and lightness of the cod (Gadus) larvae are due to the presence of a vast subcutaneous space filled with aqueous humor and extending from the head and yolk sac to the posterior end of the body. The eel larva (Anguilla) has the same vast space between the skin and muscles. All these devices undoubtedly reduce weight and impede diving. Ho and with a high specific gravity, an organism will stick to water if it presents sufficient surface resistance. This is achieved, as said, by increasing the volume and changing the shape.
Deposits of fat and oil in the body, serving as a food reserve, at the same time, reduce its specific gravity. Eggs and juveniles of many fish show this adaptation. Pelagic eggs do not stick to objects, they swim freely; many of them contain a large drop of fat on the surface of the yolk. Such are the eggs of many cod fish: the common fish (Brosmius brosme), often found in Murman; moth (Molva molva), which is caught there; such are the eggs of mackerel (Scomber scomber) and other fish.
Air bubbles of all kinds serve the same purpose - to reduce the specific gravity. This includes, of course, the swim bladder.
Eggs are built of a completely different type, submerged - demersal, developing at the bottom. They are larger, heavier, darker, while pelagic eggs are transparent. Their shell is often sticky, so that these eggs stick to rocks, algae and other objects, or to each other. In some fish, like the garfish (Belone belone), the eggs are also equipped with numerous filamentous outgrowths that serve to attach to algae and to each other. In smelt (Osmerus eperlanus), eggs are attached to rocks and rocks by the outer shell of the egg, which is detached, but not completely, from the inner membrane. Large eggs of sharks and rays also adhere. The eggs of some fish, such as salmon (Salmo salar), are large, separate and do not stick to anything.
Bottom fish, or benthos fish. Fish living at the bottom near the coast, as well as pelagic fish, represent several types of adaptation to their living conditions. Their main conditions are as follows: first, the constant danger of being thrown by the surf or in a storm ashore. Hence the need arises to develop the ability to hold onto the bottom. Secondly, the danger of being smashed against stones; hence the need to acquire armor. Fish living on the muddy bottom and digging in it develop various adaptations: some for digging and for moving in the mud, and others for catching prey, buried in the mud. Some fish have devices for hiding among algae and corals growing among the banks and at the bottom, while others - for burying in the sand at low tide.
We distinguish between the following types of bottom fish.
The type is dorsoventrally flattened. The body is compressed from the dorsal side to the ventral side. The eyes are moved to the upper side. The fish can nestle closely to the bottom. Example: stingrays (Raja, Trygon, etc.), and from bony fish - sea devil (Lophius piscatorius).
Longtail type. The body is strongly elongated, the highest part of the body is behind the head, gradually becomes thinner and ends in a sharpness. The apal and dorsal fins form a long fin fringe. The type is common among deep-sea fish. Example: long-tailed (Macrurus norvegicus) (Fig. 190).
Compressed asymmetric type. The body is laterally compressed, bordered by long dorsal and anal fins. The eyes are on one side of the body. In youth, they have a squeezed-symmetrical body. There is no swim bladder, they stay at the bottom. This includes the flounder family (Pleuronectidae). Example: turbot (Rhombus maximus).
The type is acne-like. The body is very long, serpentine; paired fins are rudimentary or absent. Bottom fish. The movement along the bottom created the same shape that among reptiles we see in snakes. Examples include eel (Anguilla anguilla), lamprey (Petromyzon fluviatilis).
The type is asteroleptic. The front half of the body is enclosed in a bony armor, which reduces active movement to a minimum. The body is triangular in cross-section. Example: box body (Ostracion cornutus).
Special conditions prevail at great depths: enormous pressure, absolute absence of light, low temperature (up to 2 °), complete calmness and absence of movement in the water (except for the very slow movement of the entire mass of water from the Arctic seas to the equator), and the absence of plants. These conditions impose a sharp stamp on the organization of fish, creating a special character of the deep fauna. Their muscular system is poorly developed, the bone is soft. The eyes are sometimes reduced to complete disappearance. In those deep-seated fish in which the eyes are preserved, the retina is similar in the absence of cones and the position of the pigment to the eye of nocturnal animals. Further, deep-seated fish are distinguished by a large head and slender body, thinning towards the end (long-tail type), a large expandable stomach and very large teeth in the mouth (Fig. 191).
Deep-seated fish can be divided into benthic and bathypelagic fish. Bottom fish of depths include representatives of stingrays (cat. Turpedinidae), flounders (family Pleuronectidae), hand-footed fishes (family Pediculati), shell-cheeks (Cataphracti), long-tailed (family Macruridae), eelpouts (family Zoarcidae), cod (family Zoarcidae) Gadidae), etc. Ho both among bathypelagic and coastal fish there are representatives of these families. It is not always easy to draw a sharp, distinct boundary between deep-seated and coastal forms. Many forms are found here and there. Also, the depth at which bathypelagic forms are encountered varies widely. Of the bathypelagic fish, mention should be made of the luminous anchovies (Scopelidae).
Bottom fish feed on sedentary animals and their remains; it does not require expenditure of energy, and bottom fish usually keep in large schools. On the contrary, bathypelagic fish find their food with difficulty and keep one by one.
Most of the commercial fish belong to either the littoral or pelagic fauna. Some cod (Gadidae), mullet (Mugilidae), flounder (Pleuronectidae) belong to the coastal zone; tuna (Thynnus), mackerel (Scombridae) and the main commercial fish - herring (Clupeidae) - belong to the pelagic fauna.
Of course, not all fish necessarily belong to one of these types. Many fish only approach one or another of them. A clearly expressed type of structure is the result of adaptation to certain, strictly isolated conditions of habitat and movement. And such conditions are not always well expressed. On the other hand, it takes a long time for this or that type to develop. A fish that has recently changed its habitat may partly lose its former adaptive type, but not yet develop a new one.
Freshwater does not have the same variety of living conditions that is observed in the sea, however, there are several types among freshwater fish. For example, the dace (Leuciscus leuciscus), which prefers to stick to a more or less strong current, has a type approaching fusiform. On the contrary, the bream (Abramis bama) or crucian carp (Carassius carassius) belonging to the same family of cyprinids (Cyprinidac) - sedentary fish living among aquatic plants, roots and under steep fishes - have a clumsy body, squeezed from the sides, like in reef fish. The pike (Esox lucius), a predator rapidly rushing towards its prey, resembles the arrow-shaped type of nekton fish; living in type and silt, the loach (Misgurnus fossilis) reptile at the bottom has a more or less eel-like shape. The sterlet (Acipenser ruthenus), constantly reptile along the bottom, resembles the longtail type.
