Deep-sea fish are amazing representatives of the world fauna. Arseny Knyazkov "Fish World"

Fish are the oldest vertebrate chordates that inhabit exclusively aquatic habitats, both salt and fresh water. Compared to air, water is a denser habitat.

In the external and internal structure, fish have adaptations for life in water:

1. Body shape is streamlined. The wedge-shaped head smoothly passes into the body, and the body into the tail.

2. The body is covered with scales. Each scale with its anterior end is immersed in the skin, and with its posterior end it rests 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. 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 ventral) and unpaired fins (dorsal, anal, caudal) provide stability and movement in the water.

4. A special outgrowth of the esophagus helps fish to stay in the water column - swimming bladder. It is filled with air. By changing the volume of the swim bladder, fish change their specific gravity (buoyancy), i.e. become lighter or heavier than water. As a result, they can stay at different depths for a long time.

5. The respiratory organs of fish are gills, which absorb oxygen from the water.

6. The sense organs are adapted to life in water. The eyes have a flat cornea and a spherical lens - this allows the fish to see only close objects. The olfactory organs open outward through 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. Sensory cells are located at the bottom of the tubules. The lateral line of the fish perceive all movements of the water. Due to this, they react to the movement of objects around them, to various 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 emergence diabetes? Explain preventive measures for 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 about the factors 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 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. For the development of the disease, a certain influence of circumstances, the environment, which manifests itself in relative risk factors, is necessary.

Relative factors in the development of diabetes include obesity, metabolic disorders, and a number of concomitant diseases and conditions: atherosclerosis, coronary heart disease, hypertension, chronic pancreatitis, stress, neuropathy, 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 - This is a condition characterized by high blood sugar levels. The modern classification of diabetes mellitus, adopted World Organization health care (WHO), distinguishes several of its types: 1st, in which the production of insulin by pancreatic b-cells is reduced; and the 2nd 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 itchy skin, weight change.

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. It is precisely in this respect that fish are extremely interesting, 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 adaptability can be observed in the aquarium.

Many millions of years ago in the Devonian seas Paleozoic era lived amazing, long extinct (with a few exceptions) crossopterygian fish (Crossopterygii), to which amphibians, reptiles, birds and mammals owe their origin. The swamps in which these fish lived began to gradually dry up. Therefore, over time, to the gill breathing they had until now, pulmonary breathing was also added. And the fish more and more adapted to breathing oxygen from 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, over many millions of years, five-fingered limbs developed from their dense, fleshy fins.

In the end, some of them adapted to life on land, although they still did not go very far from the water in which their larvae developed. This is how the first ancient amphibians arose. Their origin from lobe-finned fishes is proved by the finds of fossil remains, which convincingly show the evolutionary path of fishes to terrestrial vertebrates and thus to humans.

This is the most convincing material evidence of the adaptability of organisms to changing environmental conditions, which can only be imagined. Of course, this transformation lasted for millions of years. In the aquarium, we can observe many other kinds of adaptability, less important than those just described, but faster and therefore more obvious.

Fish are quantitatively the richest class of vertebrates. To date, over 8,000 species of fish have been described, many of which are known in aquariums. In our reservoirs, in rivers, lakes, there are about sixty species of fish, for the most part 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 its decoration either all their lives, or at least while the fish are young. With our ordinary fish, we can most easily observe how they adapt to environmental changes.

If we put a young carp about 10 cm long in a 50 x 40 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 find that the carp contained in the larger aquarium has outgrown the other one. small aquarium. Both received the same amount of the same food and, however, did not grow in the same way. In the future, both fish will stop growing altogether.

Why is this happening?

Reason - pronounced adaptability to external conditions environments. Although in a smaller aquarium appearance fish does not change, but 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 hidden irritations 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 the fish, which has been kept in a small vessel for a long time and which has therefore become sick, is placed in large swimming pool or a pond, then it will begin to catch up with what has been lost in its growth. If she does not catch up with everything, however, she can significantly increase in size and weight even in a short time.

Under the influence of different environmental conditions, fish can significantly change their appearance. So 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 more striking these external morphological differences are usually, which are caused by prolonged exposure to different environments. The fast-flowing flow of water in a river bed, or the quiet depths of a lake and a dam, equally but differently 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. Let's take, for example, the well-known veiltails. Skillful and patient Chinese, through a long and careful selection, brought out a completely different fish from a goldfish, which differed significantly from the original shape in the shape of the body and tail. The veiltail has a fairly long, often hanging, thin and split tail fin, similar to the most delicate veil. His body is rounded. Many types of veiltails have bulging and even turned up eyes. Some forms of veiltails have strange outgrowths on their heads in the form of small combs or caps. A very interesting phenomenon is the adaptive ability to change color. In the skin of fish, as in amphibians and reptiles, pigment cells, the so-called chromophores, contain countless pigment granules. Black-brown melanophores predominate in the skin of fish from chromo- tophores. Fish scales contain silver-colored guanine, which causes this very shine, which gives water world so magical beauty. Due to compression and stretching of the chromophore, a change in color of the whole animal or any part of its body can occur. These changes occur involuntarily with various excitations (fright, fight, spawning) or as a result of adaptation to a given environment. In the latter case, the perception of the situation acts reflexively on the change in color. Who had the opportunity to see flounders in the marine aquarium lying on the sand of the left or right side his flat body, he could observe how this amazing fish quickly changes its color as soon as it hits 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 the slightly modified ancient forms that have survived, such as, for example, lungfish, but also in modern fish species.

First of all, about the adaptive ability of lungfish. 3 families of these fish live 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 a 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, fish breathe normally, that is, with gills, only sometimes swallowing air, because in addition to the gills themselves, they also have special lung 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 the silt and fall into hibernation, which lasts until the first relatively large rains.

Some fish, like our brook trout, need a relatively large amount of oxygen to live. Therefore, they can only live in running water, the colder the water and the faster it flows, the better. But it has been experimentally established that forms that have been grown in an aquarium from an early age do not require running water; they should only have cooler or slightly ventilated 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 called so because of the additional organ with which they can swallow oxygen from the air. This is the most important adaptation to life in puddles, rice fields and other places with bad, decaying water. In an aquarium with crystal clean water these fish take in less air than in a cloudy water tank.

Convincing evidence of how living organisms can adapt to the environment in which they live is the viviparous fish that are very often kept in aquariums. There are many types of them, small and medium in size, variegated and less colorful. All of them have common feature- they give birth to relatively developed fry, which no longer have a yolk sac and soon after birth live independently and hunt for small prey.

Already the act of mating these fish differs significantly from spawning, because males fertilize mature eggs directly in the body of females. The latter, after a few weeks, throw out fry, which immediately swim away.

These fish live in Central and South America, often in shallow ponds and puddles, where after the end of the rains the water level drops and the water almost or completely dries up. Under such conditions, the laid eggs would die. Fish have already adapted to this so much that they can be thrown out of drying puddles with strong jumps. Jumping, in relation to the very size of their body, is greater than that of salmon. Thus, they jump until they fall into the nearest body of water. Here the fertilized female gives birth to fry. In this case, only that part of the offspring that was born in the most favorable and deep water bodies is preserved.

At the mouths of the rivers tropical Africa live more strange fish. Their adaptation has stepped so far forward that they not only crawl out of the water, but can also climb onto the roots of coastal trees. These are, for example, mudskippers from the goby family (Gobiidae). Their eyes, reminiscent of a frog's, but even more protruding, are located on the top of the head, which gives them the ability to navigate well on land, where they lie in wait for prey. In case of danger, these fish rush to the water, bending and stretching the body like caterpillars. Fish adapt to living conditions mainly by their individual body shape. This, on the one hand, is a protective device, on the other hand, due to the lifestyle of various fish species. So, for example, carp and crucian carp, feeding mainly on the bottom of motionless or inactive 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 strongly laterally compressed body, like a perch, or a torpedo-shaped body, like a pike, pikeperch or trout. This body shape, which does not represent strong water resistance, allows the fish to instantly attack prey. The prevailing majority of fish has a streamlined body shape that cuts through the water well.

Some fish have adapted, thanks to their way of life, to very special conditions, so much so that they even bear little resemblance to fish at all. So, for example, seahorses have a tenacious tail instead of a caudal fin, with which they strengthen themselves on algae and corals. They move forward not in the usual way, but due to the wave-like movement of the dorsal fin. Sea Horses so similar to environment that predators hardly notice them. They have an excellent camouflage coloration, green or brown, and most of the species have on their body long, billowing outgrowths, much like algae.

In tropical and subtropical seas, there are fish that, fleeing from their pursuers, jump out of the water and, thanks to their wide, membranous pectoral fins, glide many meters above the surface. These are the 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 archers from the rivers of southwest Asia and Australia are excellently adapted to hunting flies and other flying insects that sit on plants and various objects protruding from the water. The archer keeps near the surface of the water and, noticing the prey, splashes from the mouth with a thin water jet, knocking the insect to the surface of the water.

Some fish species from various systematically distant groups have developed over time the ability to spawn far from their habitat. These include, for example, salmon fish. Before the ice age, they inhabited the fresh waters of the basin northern seas- his original place of residence. After the melting of the glaciers, there appeared modern views salmon. 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 rivers to spawn in fresh water, from where they later return 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 autumn migrations of birds, following very specific paths. Eel behaves even more interestingly. This slippery, serpentine fish breeds in the depths Atlantic Ocean, probably at a depth of up to 6000 meters. In this cold, deep-sea desert, which is only occasionally illuminated by phosphorescent organisms, tiny, transparent, leaf-shaped eel larvae hatch from countless eggs; for three years they live in the sea before they develop into true little eels. And after that, countless juvenile eels begin their journey into the fresh water of the river, 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 a reservoir. The structure of the body gives him a good opportunity to penetrate into the very thickness of the silt, and with a lack of food, crawl on dry land into a nearby reservoir. Another interesting change in its color and shape of the eyes when moving to sea water. Initially dark eels turn to a silvery sheen on the way, and their eyes enlarge significantly. Enlargement of the eyes is observed when approaching the mouths of rivers, where the water is more brackish. This phenomenon can be induced in an aquarium with adult eels by diluting a little salt in the water.

Why do the eyes of eels enlarge when traveling to the ocean? This device makes it possible to catch every, even the smallest ray 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, such as daphnia, larvae of some mosquitoes, 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. Small, about a cm long, Anableps tetrophthalmus from South America has adapted to catching flies from the surface of the water. In order to be able to move freely right at the very surface of the water, she has a straight back, strongly elongated with one fin, like a pike, very shifted back, and her eye is divided into two almost independent parts, upper and lower. The lower part is an ordinary fish eye, and the fish looks underwater with it. Top part protrudes quite significantly forward and rises above the very surface of the water. Here, with its help, the fish, examining the surface of the water, detects fallen insects. Only some examples from the inexhaustible variety of species of adaptation of fish to the environment in which they live are given. Just like these inhabitants of the water kingdom, other living organisms are able to adapt to varying degrees in order to survive in interspecific struggle on our planet.

The conditions of life in various areas of fresh waters, and especially in the sea, leave a strong imprint on the fish living in these areas.
Fish can be divided into marine, anadromous, semi-anadromous or estuarine fish, brackish water fish, and freshwater fish. Already significant differences in salinity are important for the distribution certain types. The same is true of differences in other properties of water: temperature, lighting, depth, etc. Trout requires different water than barbel or carp; tench and crucian carp also keep in such reservoirs where perch cannot live due to too warm and muddy water; asp requires clean flowing water with fast rifts, and pike can also stay in stagnant water overgrown with grass. Our lakes, depending on the conditions of existence in them, can be distinguished as zander, bream, crucian, etc. Within 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 one or another species composition predominates in each zone. The coastal zone is richest of all. The abundance of vegetation, hence food, makes this area favorable for many fish; here they feed, here they throw an acre. The distribution of fish into zones plays an important role in fisheries. For example, burbot (Lota lota) is a demersal fish, and it is caught from the bottom with venters, but not with the flowing nets used to catch asp, etc. Most whitefish (Coregonus) feed on small planktonic organisms, mainly crustaceans. Therefore, their habitat depends on the movement of plankton. In winter, they follow the latter to the depths, but in the spring they rise to the surface. In Switzerland, biologists pointed out 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 demarcation of the zone in the sea is more pronounced. The sea, according to the living conditions that it provides for organisms, 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 the coastal to the 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 limits the area deeper than 350 m. The open sea zone will be outward from this plane and upward from another plane lying horizontally at a depth of 350 m. from this latter (Fig. 186).

Light is essential to all life. Since water transmits the rays of the sun weakly, conditions of existence unfavorable for life are created in water at a certain depth. According to the strength of illumination, three light zones are distinguished, as indicated above: euphotic, dysphotic and aphotic.
Near the coast, free-floating and bottom forms are closely mixed. Here is the cradle of marine animals, from here arise the clumsy inhabitants of the bottom and the agile swimmers of the open sea. Thus, along the coast we will meet a rather diverse mixture of types. On the other hand, the conditions of life in 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 but bottom, lying on the bottom, burrowing forms (mobile benthos) and sessile forms (sessile benthos: corals, sea anemones, tube worms, etc.).
Those organisms that can swim freely, we call pectons. The third group of organisms, deprived or almost deprived of the ability to move actively, clinging to algae or helplessly carried by the wind or currents, is called planktol. Among fish we have forms belonging to all three groups of organisms.
Nelagic fishes - nekton and plankton. Organisms that live in water independently of the bottom, not associated with it, are called non-aggressive. This group includes organisms both living on the surface of the sea and in its deeper layers; organisms that actively swim (nekton), and organisms carried by wind and currents (plankton). Deep-living pelagic animals are called batynelagic.
The conditions of life on the high seas are characterized primarily by the fact that there is no surf here, and there is no need for animals to develop devices for keeping on the bottom. The predator has nowhere to hide here, lying in wait for prey, the latter has nowhere to hide from predators. Both must rely primarily on their own speed. Most open sea fish are therefore excellent swimmers. This is the first; secondly, the color of sea water, blue in both transmitted and incident light, also affects the color of pelagic organisms in general and fish in particular.
Adaptations of nekton fish to locomotion are different. We can distinguish several types of nekton fish.
In all these types, the ability to swim quickly is achieved in various ways.
Spindle type, or torpedo-shaped. The organ of movement is the tail section of the body. An example of this type are: herring shark (Lamna cornubica), mackerel (Scomber scomber), salmon (Salmo salar), herring (Clupea harengus), cod (Gadus morrhua).
Tape type. Movements occur with the help of serpentine movements of a laterally compressed, long ribbon-like body. For the most part - the inhabitants of fairly large depths. Example: oarfish, or belt fish (Regalecus banksii).
Arrow type. The body is elongated, the snout is pointed, strong unpaired fins are carried back and arranged in the form of arrow plumage, being one with the caudal fin. Example: common garfish (Belone belone).
Sailing type. The snout is elongated, unpaired fins and general form like the previous one, the anterior dorsal fin is greatly enlarged and can serve as a sail. Example: sailboat (Histiophorus gladius, Fig. 187). The swordfish (Xiphias gladius) also belongs here.

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.
Acicular type. Active movements are weakened, performed with the help of quick body bends or undulating movements of the dorsal and anal fins. Example: pelagic needlefish (Syngnathus pelagicus) of the Sargasso Sea.
Squeezed-symmetrical type. The body is high. The dorsal and anal fins are located opposite each other, high. Pelvic fins for the most part No. Movement is very limited. Example: moon fish (Mola mola). This fish also lacks a tail fin.
He does not produce active movements, the muscles are largely atrophied.
Spherical type. The body is spherical. The body of some fish can inflate due to the swallowing of air. Example: hedgehog fish (Diodon) or deep-sea melanocet (Melanocetus) (Fig. 188).

There are no true planktonic forms among adult fish. Ho they are found among planktonic eggs and larvae of fish leading a planktonic lifestyle. The ability of an organism to float on water depends on a number of factors. First of all, the specific gravity of water is important. An organism floats on water, according to the law of Archimedes, if its specific gravity is not greater than the specific gravity of water. If the specific gravity is greater, then the organism sinks at a rate proportional to the difference in specific gravity. The rate of sinking, 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 hand, on what is called the 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 water counteract sinking. Excellent examples of such a change are, as is well known, copepods and radiolarians. In the eggs and larvae of fish we observe the same phenomenon.
Pelagic eggs are mostly small. The eggs of many pelagic fish are equipped with filamentous outgrowths that prevent them from diving, for example, the eggs of mackerel (Scombresox) (Fig. 189). The larvae of some fish that lead a pelagic lifestyle have a device for holding on to the surface of the water in the form of long threads, 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 stretched to enormous sizes by liquid, which, of course, by reducing the specific gravity, also helps to keep the larvae on the water.

Another condition affects the ability of organisms to float on water: osmotic pressure, which depends on temperature and salinity. With a high content of salts in the cell, the latter absorbs water, and although it becomes heavier, its specific gravity decreases. Hitting more salt water, the cell, on the contrary, having decreased in volume, will become heavier. 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 deeper and, finally, sit on the bottom. The transparency and lightness of cod larvae (Gadus) are due to the presence of a vast subcutaneous space filled with aqueous fluid and stretching 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 adaptations undoubtedly reduce weight and prevent immersion. Ho and with a large specific gravity, an organism will float on water if it presents sufficient surface resistance. This is achieved, as said, by increasing the volume and changing the shape.
The 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 exhibit this adaptation. Pelagic eggs do not stick to objects, they swim freely; many of them contain a large fatty droplet on the surface of the yolk. Such are the eggs of many cod fish: the common menka (Brosmius brosme), often found in Murman; molva (Molva molva), which is caught there; such are the eggs of mackerel (Scomber scomber) and other fish.
All kinds of air bubbles serve the same purpose - to reduce the specific gravity. This includes, of course, the swim bladder.
Eggs are built according to a completely different type, sinking - demersal, developing at the bottom. They are larger, heavier, dark, while pelagic eggs are transparent. Their shell is often sticky, so that such eggs stick to rocks, algae and other objects, or to each other. In some fish, like the garfish (Belone belone), the eggs are also provided with numerous filamentous outgrowths that serve to attach to algae and to each other. In smelt (Osmerus eperlanus), eggs are attached to stones and rocks by means of an outer shell of the egg, which separates, but not completely, from the inner membrane. Large eggs of sharks and rays also stick. The eggs of some fish, such as salmon (Salmo salar), are large, separate and do not stick to anything.
Bottom fish, or benthic fish. Fish living near the bottom near the coast, as well as pelagic ones, represent several types of adaptation to the conditions of their life. Their main conditions are as follows: firstly, the constant danger of being thrown ashore by the surf or into a storm. Hence the need to develop the ability to hold on to the bottom arises. Secondly, the danger of being crushed against stones; hence the need to acquire armor. Fish living on the muddy bottom and burrowing in it develop various adaptations: some for digging and for moving in the mud, and others for catching prey by burrowing into the mud. Some fish have adaptations to hide among the algae and corals growing along the coast and at the bottom, while others have to burrow into the sand at low tide.
We distinguish the following types of bottom fish.
Dorsoventrally flattened type. The body is compressed from the dorsal side to the ventral side. The eyes have been moved to the top. The fish can nestle close 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 sharp point. Apial and dorsal fins form a long fin margin. The type is common among deep sea fish. Example: longtail (Macrurus norvegicus) (Fig. 190).
The type is compressed-asymmetric. The body is compressed from the sides, bordered by long dorsal and anal fins. Eyes on one side of the body. In youth, they have a compressed-symmetrical body. There is no swim bladder, they stay at the bottom. This includes the flounder family (Pleuronectidae). Example: turbot (Rhombus maximus).

Acne type. The body is very long, serpentine; paired fins rudimentary or absent. Bottom fish. The movement along the bottom created the same shape that we see among snakes among reptiles. Examples are eel (Anguilla anguilla), lamprey (Petromyzon fluviatilis).
Asterolepiform type. The front half of the body is enclosed in a bony armor, which reduces active movements to a minimum. The body is triangular in section. Example: boxfish (Ostracion cornutus).
Special conditions prevail at great depths: enormous pressure, absolute absence of light, low temperature (up to 2°), complete calmness and absence of movements in the water (except for the very slow movement of the entire mass of water from the Arctic seas to the equator), the absence of plants. These conditions leave a strong imprint on the organization of fish, creating a special character of the deep fauna. The muscular system is poorly developed in them, the bone is soft. The eyes are sometimes reduced to complete disappearance. In those deep-seated fish in which eyes are preserved, the retina, in the absence of cones and the position of the pigment, is similar to the eye of nocturnal animals. Further, deep-seated fish differ big head and a thin body, thinning towards the end (long-tail type), a large distensible stomach and very large teeth in the mouth (Fig. 191).

Deep-sea fish can be divided into benthic and bathypelagic fish. Bottom fish of the depths include representatives of rays (cat. Turpedinidae), flounders (family Pleuronectidae), hand-finned fish (family Pediculati), armor-cheeked fish (Cataphracti), long-tailed fish (family Macruridae), eelpout (family Zoarcidae), cod (family Gadidae) and others. 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 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, the luminous anchovies (Scopelidae) should be mentioned.
Bottom fish feed on sedentary animals and their remains; this does not require the expenditure of strength, and bottom fish usually keep in large schools. On the contrary, bathypelagic fish find their food with difficulty and stay alone.
Most 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 major 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 pronounced 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 to develop one type or another. A fish that has recently changed its habitat may lose some of its former adaptive type, but not yet to develop a new one.
In fresh water, there is not the variety of living conditions that is observed in the sea, however, several types are found among freshwater fish. For example, the dace (Leuciscus leuciscus), which prefers to stay on a more or less strong current, has a type approaching a fusiform. On the contrary, belonging to the same family of cyprinids (Cyprinidac), bream (Abramis brama) or crucian carp (Carassius carassius) - sedentary fish living among aquatic plants, roots and under steeps - have a clumsy body, squeezed from the sides, like reef fish. The pike (Esox lucius), a fast-moving predator, resembles the arrow-shaped type of nekton fish; living in the type and silt, the loach (Misgurnus fossilis) reptiles near the bottom has a more or less eel-like shape. The sterlet (Acipenser ruthenus), which constantly crawls along the bottom, resembles a type of longtail.

The amazing variety of shapes and sizes of fish is explained by long history their development and high adaptability to the conditions of existence.

The first fish appeared several hundred million years ago. Now existing fish bear little resemblance to their ancestors, but there is a certain similarity in the shape of the body and fins, although the body of many primitive fish was covered with a strong bony shell, and highly developed pectoral fins resembled wings.

ancient fish became extinct, leaving their traces only in the form of fossils. From these fossils, we make guesses, assumptions about the ancestors of our fish.

It is even more difficult to talk about the ancestors of fish that left no traces. There were also fish that had no bones, no scales, no shells. Similar fish still exist. These are lampreys. They are called fish, although, in the words of the famous scientist L. S. Berg, they differ from fish, like lizards from birds. Lampreys do not have bones, they have one nasal opening, the intestines look like a simple straight tube, the mouth is in the form of a round sucker. In the past millennia, there were many lampreys and related fish, but they are gradually dying out, giving way to more adapted ones.

Sharks are also fish ancient origin. Their ancestors lived more than 360 million years ago. Internal skeleton sharks are cartilaginous, but on the body there are solid formations in the form of spikes (teeth). In sturgeons, the body structure is more perfect - there are five rows of bone bugs on the body, there are bones in the head section.

According to the numerous fossils of ancient fish, one can trace how the structure of their body developed and changed. However, it cannot be assumed that one group of fish directly converted to another. It would be a gross mistake to say that sturgeons originated from sharks, and teleosts from sturgeons. We must not forget that, in addition to the named fish, there were a huge number of others, which, unable to adapt to the conditions of the nature surrounding them, died out.

Modern fish also adapt to natural conditions, and in the process of this, slowly, sometimes imperceptibly, their lifestyle and body structure change.

An amazing example of high adaptability to environmental conditions is represented by lungfish. Ordinary fish breathe with gills, which consist of gill arches with gill rakers and gill filaments attached to them. Lungfish, on the other hand, can breathe with both gills and “lungs” - peculiarly arranged swimming ones and hibernates. In such a dry nest, it was possible to transport protopterus from Africa to Europe.

Lepidosiren inhabits the swampy waters of South America. When reservoirs are left without water during a drought lasting from August to September, lepidosiren, like protopterus, burrows into silt, falls into a stupor, and its life is supported by bubbles. The bubble-lung of lungfish is replete with folds and partitions with many blood vessels. It resembles an amphibian lung.

How to explain this structure of the respiratory apparatus in lungfish? These fish live in shallow water bodies, which dry out for quite a long time and become so poor in oxygen that breathing with gills becomes impossible. Then the inhabitants of these reservoirs - lungfish - switch to breathing with the lungs, swallowing the outside air. When the reservoir completely dries up, they burrow into the silt and experience drought there.

There are very few lungfish left: one genus in Africa (protopterus), another in America (lepidosiren) and a third in Australia (neoceratod, or scaly).

Protopterus inhabits fresh water bodies of Central Africa and has a length of up to 2 meters. During the dry period, it burrows into the silt, forming a chamber (“cocoon”) of clay around itself, content with an insignificant amount of air penetrating here. Lepidosiren is a large fish, reaching 1 meter in length.

The Australian flake is somewhat larger than the lepidosiren, lives in quiet rivers, heavily overgrown with aquatic vegetation. When the water level is low (dry weather) time) the grass begins to rot in the river, the oxygen in the water almost disappears, then the flake plant switches to breathing atmospheric air.

All listed lungfish are consumed by the local population for food.

Each biological feature has some significance in the life of the fish. What kind of appendages and adaptations do fish have for protection, intimidation, attack! A wonderful device has a small bitter fish. By the time of reproduction, a long tube grows in the female bitterling, through which she lays eggs in the cavity of a bivalve shell, where the eggs will develop. This is similar to the habits of a cuckoo, throwing its eggs into other people's nests. It is not so easy to get mustard caviar from hard and sharp shells. And the bitter man, having dumped his care on others, hurries to put away his cunning device and again walks in the free space.

In flying fish, capable of rising above the water and flying over fairly long distances, sometimes up to 100 meters, the pectoral fins have become like wings. Frightened fish jump out of the water, spread their fins-wings and rush over the sea. But an air walk can end very sadly: birds of prey often attack the little birds.

Flies are found in the temperate and tropical parts of the Atlantic Ocean and the Mediterranean Sea. Their size is up to 50 centimeters V.

Longfins living in tropical seas are even more adapted to flying; one species is also found in the Mediterranean Sea. Longfins are similar to herring: the head is sharp, the body is oblong, the size is 25-30 centimeters. The pectoral fins are very long. Longfins have huge swim bladders (the length of the bladder is more than half the length of the body). This device helps the fish stay in the air. Longfins can fly over distances exceeding 250 meters. When flying, the fins of longfins, apparently, do not wave, but act as a parachute. The flight of a fish is similar to the flight of a paper dove, which is often launched by children.

Jumping fish are also wonderful. If in flying fish the pectoral fins are adapted for flying, then in jumpers they are adapted for jumping. Small jumping fish (their length is not more than 15 centimeters), living in coastal waters mainly of the Indian Ocean, can leave water for quite a long time and get their own food (mainly insects), jumping on land and even climbing trees.

The pectoral fins of jumpers are like strong paws. In addition, the jumpers have another feature: the eyes placed on the head outgrowths are mobile and can see in the water and in the air. During a land journey, the fish tightly covers the gill covers and thus protects the gills from drying out.

No less interesting is the creeper, or climbing perch. This is a small (up to 20 centimeters) fish that lives in the fresh waters of India. Its main feature is that it can crawl away on land for a long distance from the water.

Creepers have a special supra-gill apparatus, which the fish uses when breathing air in cases where there is not enough oxygen in the water or when it moves overland from one reservoir to another.

Aquarium fish macropods, fighting fish and others also have a similar supragillary apparatus.

Some fish have luminous organs that allow them to quickly find food in the dark depths of the seas. Luminous organs, a kind of headlights, in some fish are located near the eyes, in others - at the tips of the long processes of the head, and in others, the eyes themselves emit light. An amazing property - the eyes both illuminate and see! There are fish that radiate light with their whole body.

In tropical seas, and occasionally in the waters of the Far Eastern Primorye, one can find interesting sticky fish. Why such a name? Because this fish is able to stick, stick to other objects. There is a large suction cup on the head, with the help of which the stick sticks to the fish.

Not only does the sticky use free transport, the fish also receive a “free” lunch, eating the remnants of the table of their drivers. The driver, of course, is not very pleasant to travel with such a “rider” (the length of the stick reaches 60 centimeters), but it is not so easy to get rid of it either: the fish sticks tightly.

Shore dwellers use this ability to trap turtles. A cord is tied to the tail and the fish is put on the turtle. The sticky quickly sticks to the turtle, and the fisherman lifts the sticky together with the prey into the boat.

In the fresh waters of the basins of the tropical Indian and Pacific Oceans live small fish archers. The Germans call it even more successful - "Schützenfish", which means a shooter-fish. The archer, swimming near the shore, notices an insect sitting on the coastal or water grass, draws water into his mouth and lets a stream into his "trading" animal. How not to call a archer a shooter?

Some fish have electrical organs. Known American electric catfish. The electric stingray lives in the tropical parts of the oceans. Its electric shocks can knock a grown man off his feet; small aquatic animals often die from the blows of this stingray. The electric stingray is a rather large animal: up to 1.5 meters in length and up to 1 meter wide.

Strong electric shocks are also capable of inflicting an electric eel, reaching 2 meters in length. A German book depicts frenzied horses attacking electric eels in the water, although there is no small part of the artist's imagination here.

All of the above and many other features of fish have been developed over thousands of years as necessary means of adapting to life in aquatic environment.

It is not always so easy to explain why one or another device is needed. Why, for example, does a carp need a strong serrated fin ray, if it helps to entangle the fish in the net! Why do we need such long tails for a wide-mouthed and a whistle? Undoubtedly, this has its own biological meaning, but not all the mysteries of nature have been solved by us. We have given a very small number of interesting examples, but they all convince of the expediency of various adaptations of animals.

In flounder, both eyes are on one side of a flat body - on the one that is opposite to the bottom of the reservoir. But they will be born, come out of eggs, flounders with a different arrangement of eyes - one on each side. In larvae and fry of flounder, the body is still cylindrical, and not flat, like in adult fish. The fish lies on the bottom, grows there, and its eye from the bottom side gradually passes to the upper side, on which both eyes eventually end up. Surprising but understandable.

The development and transformation of the eel is also surprising, but less understood. The eel, before acquiring its characteristic serpentine form, undergoes several transformations. At first it looks like a worm, then it takes the form of a tree leaf and, finally, the usual shape of a cylinder.

In an adult eel, the gill slits are very small and tightly covered. The feasibility of this device is that it is tightly covered. the gills dry out much more slowly, and with moistened gills, the eel can remain alive for a long time without water. There is even a fairly plausible belief among the people that the eel crawls through the fields.

Many fish are changing before our eyes. The offspring of large crucian carp (weighing up to 3-4 kilograms), transplanted from the lake into a small pond with little food, does not grow well, and adult fish look like “dwarfs”. This means that the adaptability of fish is closely related to high variability.

I, Pravdin "The story of the life of fish"