How are fish adapted to life in the water? Deep-sea fish are amazing representatives of the world fauna How fish are adapted to the aquatic environment

Deep sea fish are considered one of the most amazing creatures on the planet. Their uniqueness is explained primarily by the harsh conditions of existence. That is why the depths of the world's oceans, and especially deep-sea depressions and trenches, are not at all densely populated.

and their adaptation to the conditions of existence

As already mentioned, the depths of the oceans are not as densely populated as, say, the upper layers of the water. And there are reasons for this. The fact is that the conditions of existence change with depth, which means that organisms must have some adaptations.

1. Life in the dark. With depth, the amount of light decreases sharply. It is believed that the maximum distance that a sunbeam travels in water is 1000 meters. Below this level, no traces of light were found. Therefore, deep-sea fish are adapted to life in total darkness. Some fish species do not have functioning eyes at all. The eyes of other representatives, on the contrary, are very strongly developed, which makes it possible to capture even the weakest light waves. Another interesting device is luminescent organs that can glow using the energy of chemical reactions. Such light not only facilitates movement, but also lures potential prey.
2. High pressure. Another feature of the deep-sea existence. That is why the internal pressure of such fish is much higher than that of their shallow relatives.
3. Low temperature. With depth, the temperature of the water decreases significantly, so the fish are adapted to life in such an environment.
4. Lack of food. Since the diversity of species and the number of organisms decreases with depth, there is, accordingly, very little food left. Therefore, deep-sea fish have supersensitive organs of hearing and touch. This gives them the ability to detect potential prey at a great distance, which in some cases is measured in kilometers. By the way, such a device makes it possible to quickly hide from a larger predator.

You can see that the fish living in the depths of the ocean are truly unique organisms. In fact, a huge area of ​​the world's oceans is still unexplored. That is why the exact number of deep-sea fish species is unknown.

Diversity of fish living in the water depths

Although modern scientists know only a small part of the population of the depths, there is information about some very exotic inhabitants of the ocean.

Bathysaurus- the deepest predatory fish that live at a depth of 600 to 3500 m. They live in tropical and subtropical water spaces. This fish has almost transparent skin, large, well-developed sensory organs, and its oral cavity is littered with sharp teeth (even the tissues of the palate and tongue). Representatives of this species are hermaphrodites.

viper fish- Another unique representative of the underwater depths. It lives at a depth of 2800 meters. It is these species that inhabit the depths. The main feature of the animal is its huge fangs, which are somewhat reminiscent of the poisonous teeth of snakes. This species is adapted to existence without constant food - the stomachs of fish are so stretched that they can swallow whole a living creature much larger than themselves. And on the tail of the fish there is a specific luminous organ, with the help of which they lure prey.

Angler- a rather unpleasant-looking creature with huge jaws, a small body and poorly developed muscles. It lives on Since this fish cannot actively hunt, it has developed special adaptations. has a special luminous organ that releases certain chemicals. Potential prey reacts to light, swims up, after which the predator swallows it completely.

In fact, there are much more depths, but not much is known about their way of life. The fact is that most of them can exist only under certain conditions, in particular, at high pressure. Therefore, it is not possible to extract and study them - when they rise to the upper layers of the water, they simply die.

The amazing variety of shapes and sizes of fish is explained by the long history of 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.

The oldest fish died out, 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 of the most ancient origin. Their ancestors lived more than 360 million years ago. The internal skeleton of sharks is cartilaginous, but there are solid formations in the form of spikes (teeth) on the body. 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, 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 bladder-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 a 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 in.

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 the 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, small archer fish live. 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 the 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 curious 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 much more slowly, and with moistened gills, the eel can remain alive for a long time without water. There is even a rather 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"

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 onset of 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 by the World Health Organization (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 adaptation of fish to life in water is manifested, first of all, in the streamlined shape of the body, which creates the least resistance when moving. This is facilitated by a cover of scales covered with mucus. The caudal fin as an organ of movement and the pectoral and ventral fins provide excellent fish maneuverability. The lateral line allows you to confidently navigate even in muddy water, without bumping into obstacles. The absence of external hearing organs is associated with good sound propagation in the aquatic environment. The vision of fish allows them to see not only what is in the water, but also to notice the threat on the shore. The sense of smell allows you to detect prey at great distances (for example, sharks).

The respiratory organs, the gills, provide the body with oxygen in conditions of low oxygen content (compared to air). The swim bladder plays the role of a hydrostatic organ, allowing the fish to maintain body density at various depths.

Fertilization is external, except for sharks. Some fish have live birth.

Artificial breeding is used to restore the population of migratory fish in rivers with hydroelectric power stations, primarily in the lower reaches of the Volga. Producers going to spawn are caught at the dam, fry are grown in closed reservoirs and released into the Volga.

Carp is also bred for commercial purposes. Silver carp (strains off single-celled algae) and grass carp (feeds on underwater and surface vegetation) make it possible to obtain products with minimal costs for feeding.

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. Fishes 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 adaptability can be observed in the aquarium.

Many millions of years ago, in the Devonian seas of the Paleozoic era, there lived amazing, long-extinct (with a few exceptions) lobe-finned 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 place 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 carp from the 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 environmental conditions. Although in a smaller aquarium the appearance of the 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 a fish, which has been kept in a small vessel for a long time and which therefore has become ill, is placed in a large pool or 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 stream 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 brilliance that gives the water world such a 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. Anyone who had the opportunity to see flounders in a marine aquarium lying on the sand with the left or right side of their flat body 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 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 clear water, these fish take in less air than in an aquarium with cloudy water.

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 a 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.

Stranger fish live in the mouths of the rivers of tropical Africa. 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. Seahorses are so similar to the 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 northern seas basin - their original habitat. After the melting of the glaciers, modern salmon species also 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 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, snake-like fish breeds in the depths of the Atlantic Ocean, probably up to 6,000 meters deep. 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. The upper 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 the interspecific struggle on our planet.