Skin pigmentation and coloration of fish. Why in the animal world is the color of males brighter and more attractive than that of females? Naturally, the color of the body of the fish is closely related to the lighting conditions.
The fish that inhabit the caves are very diverse. At present, representatives of a number of groups of cyprinids are known in the caves - Cypriniformes (Aulopyge, Paraphoxinus, Chondrostoma, American catfish, etc.), Cyprinodontiformes (Chologaster, Troglichthys, Amblyopsis), a number of species of gobies, etc.
Illumination conditions in water differ from those in air not only in intensity, but also in the degree of penetration into the depth of water of individual rays of the spectrum. As is known, the coefficient of absorption by water of rays with different wavelengths is far from being the same. Red rays are most strongly absorbed by water. When passing a layer of water of 1 m, 25% of red rays are absorbed and only 3% of violet. However, even violet rays at a depth of more than 100 m become almost indistinguishable. Consequently, at the depths of the fish poorly distinguish colors.
The visible spectrum perceived by fish is somewhat different from the spectrum perceived by terrestrial vertebrates. At different fish there are differences related to the nature of their habitat. Fish species living in the coastal zone and in
Rice. 24. cave fish(from top to bottom) - Chologaster, Typhlichthys; Amblyopsis (Cyprinodontiformes)
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 from 485 to 720 mkm, and the stellate stingray that keeps 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). At the same time, it should be noted that the reduction in visibility occurs, first of all, due to the long-wavelength part of the spectrum (Protasov, 1961).
The fact that most species of fish distinguish colors is proved by a number of observations. Apparently, only some cartilaginous fishes (Chondrichthyes) and cartilaginous ganoids (Chondrostei) do not distinguish colors. The rest of the fish are well distinguished
colors, which has been proven, in particular, by many experiments using a conditioned reflex technique. For example, the minnow - Gobio gobio (L.) - could be taught to take food from a cup of a certain color.
It is known that fish can change the color and pattern of the skin depending on the color of the ground on which they are located.
At the same time, if the fish, accustomed to black soil and having changed color accordingly, were given a choice of a number of soils of different colors, then the fish usually chose the soil to which it was. accustomed to and the color of which corresponds to the color of her skin.
Especially drastic changes in body color on various soils are observed in flounders. At the same time, 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 is not yet clear. It is only known that a change in color occurs as a result of a corresponding irritation of the eye. Semtser (Sumner, 1933), putting transparent colored caps on the fish's eyes, 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 is on the ground of another color, changes the color of the body according to the background on which the head is located (Fig. 25). "
Naturally, the color of the body of a fish is closely related to the conditions of illumination.
It is usually customary to distinguish the following main types of fish coloration, which are an adaptation to certain habitat conditions.
Rice. 25. The dependence of the color of the body of a flounder on the color of the soil on which its head is located
Pelagic coloration - bluish or greenish back 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 noticeable from above, and the silvery sides and belly are poorly visible from below against the background of a mirror surface.
Overgrown painting- brownish, greenish or yellowish back and usually transverse stripes or stains on the sides. This coloration is characteristic of fish in thickets or coral reefs. Sometimes these fish, especially in tropical zone, can be colored very brightly.
Examples of fish with overgrown coloration are: common perch and pike - from freshwater forms; sea scorpion ruff, many wrasses and coral fish are from marine.
Bottom coloring- dark back and sides, sometimes with darker streaks and a light belly (in flounders, the side facing the ground is light). In bottom fish living above the pebbly soil of rivers with clear water, usually on the sides of the body there are black heels, 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 salmon fry in the river period of life, grayling fry, common minnow and other fish. This coloration makes the fish hardly noticeable against the background of pebbly soil in transparent flowing water. Bottom fish in stagnant waters usually do not have bright dark spots on the sides of the body, or they have blurred outlines.
The schooling coloration of fish is especially prominent. This coloration facilitates the orientation of individuals in the flock to each other. It appears as either one or more spots on the sides of the body or on the dorsal fin, or as dark stripe along the body. An example is the coloration of the Amur minnow - Phoxinus lagovskii Dyb., juveniles of the prickly bitterling - Acanthorhodeus asmussi Dyb., some herring, haddock, etc. (Fig. 26).
The coloration of deep-sea fishes 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 under water seems black and is poorly visible to predators.
A slightly different color pattern is observed in deep sea fish having organs of luminescence on the body. These fish have a lot of guanine in their skin, which gives the body a silvery sheen (Argyropelecus, 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. Thus, for example, the coloration of juvenile salmon in a river has the character of a channel type, when it descends into the sea, it is replaced by a pelagic one, and when the fish return back to the river for breeding, it again acquires a channel character. Coloring can change during the day; Thus, in some representatives of Characinoidei, (Nannostomus), the coloration is flocking during the day - a black stripe along the body, and at night transverse striping appears, i.e., the color becomes overgrown.
The so-called mating coloration in fish is often
Rice. 26, Types of schooling coloration in fish (from top to bottom): Amur minnow - Phoxinus lagowsku Dyb.; prickly bitterling (juvenile) - Acanthorhodeus asmussi Dyb.; haddock - Melanogrammus aeglefinus (L.)
protective device. Mating 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 saita (Brev.), etc. Some<рыбы, как например сазан, избегают света. На свет обычно привлекаются рыбы, которые питаются, ориентируясь при помощи органа зрения, главным образом так называемые «зрительные планктофаги». Меняется реакция на свет и у рыб, находящихся в разном биологическом состоянии. Так, самки анчоусовидной кильки с текучей икрой на свет не привлекаются, а отнерестовавшие или находящиеся в преднерестовом состоянии идут на свет. Меняется у многих рыб характер реакции на свет и в процессе индивидуального развития. Молодь лососей, гольяна и некот- рых других рыб прячется от света под камни, что обеспечивает ей сохранность от врагов. У пескороек - личинок миноги (кру- глоротые), у которых хвост несет светочувствительные клетки,- эта особенность связана с жизнью в грунте. Пескоройки на освещение хвостовой области реагируют плавательными движениями, глубже закапываясь в грунт.
What are the reasons for the reaction of fish to light? There are several hypotheses on this issue. J. Loeb considers the attraction of fish to light as a forced, non-adaptive movement - as a phototaxis. Most researchers consider the reaction of fish to light as an adaptation. Franz (cited by Protasov) believes that light has a signal value, in many cases serving as a signal of danger. S. G. Zusser (1953) considers that the reaction of fish to light is a food reflex.
Undoubtedly, in all cases, the fish reacts to light adaptively. In some cases, this may be a defensive reaction when the fish avoids the light, in other cases, the approach to the light is associated with the extraction of food. At present, a positive or negative reaction of fish to light is used in fishing (Borisov, 1955). The fish, attracted by the light, forming clusters around the light source, are then caught either with net tools or pumped onto the deck by a pump. Fish that react negatively to light, such as carp, with the help of light are expelled from places that are inconvenient for fishing, for example, from burrowed sections of the pond.
The importance of light in the life of fish is not limited to its connection with vision.
Illumination is 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 (those adapted to development in the light are marked in the dark, and vice versa). This is clearly shown by N. N. Disler (1953) using the example of chum salmon development in the light.
Light also has an effect on the course of maturation of the reproductive products of fish. Experiments on the American char - Salvelintis foritinalis (Mitchiil) showed that in experimental fish exposed to enhanced lighting, maturation occurs earlier than in controls that were under normal light. However, in fish under high mountain conditions, apparently, just as in some mammals under conditions of artificial illumination, light, after stimulating the increased 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 illumination intensity during 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 certain times, is largely due to the intensity of insolation.
A peculiar protective adaptation from light is observed in the larvae of many pelagic fish. Thus, in the larvae of the herring 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 sac, the pigment above the neural tube disappears in fry. Interestingly, closely related species that have bottom eggs and larvae that stay 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 gambusia (Gambusia affinis Baird. et Gir.),. have shown that in mosquito fish deprived of light, vitamin deficiency develops rather quickly, causing, first of all, the loss of the ability to reproduce.
The coloration of fish, including the color pattern, is an important signal. The main function of color is to help members of the same species find and identify each other as potential sexual partners, rivals, or members of the same pack. Demonstration of a certain coloration may not go further than this.
Fish of certain species take on one color or another, demonstrating their readiness for spawning. The bright colors of the fins make a proper impression on potential sexual partners. Occasionally, a mature female will develop a brightly colored area on her belly, emphasizing its rounded shape and indicating that it is filled with caviar. Fish that have a specific bright spawning coloration may appear dull and inconspicuous when not spawning. A noticeable appearance makes the fish more vulnerable to predators, and unmasks predatory fish.
Spawning coloration may also serve as a stimulus for competition, for example in competition for a spawning partner or for spawning territory. The preservation of such coloration after the end of spawning would be completely meaningless, and perhaps even clearly unfavorable for schooling fish.
Some fish have an even more highly developed "language" of coloration, and they can use it, for example, to demonstrate their status in a group of fish of the same species: the brighter and more challenging the coloring and pattern, the higher the status. They may also use coloration to demonstrate threat (bright coloration) or submission (dim or less bright coloration), often accompanied by gestures, body language, and fish.
Some fish showing parental care for offspring have a special coloration when guarding young. This coloration of the watchman is used to warn intruders or to draw attention to themselves, distracting from the fry. Scientific experiments have shown that parents use certain colors to attract fry (to make it easier for them to find their parents). Even more remarkable is that some fish use their body and fin movements, as well as coloration, to give various instructions to their fry, for example: "Swim here!", "Follow me" or "Hide at the bottom!"
It must be assumed that each species of fish has its own "language", corresponding to their special way of life. However, there is strong evidence that closely related fish species clearly understand each other's basic signals, although they most likely do not have the slightest idea what the representatives of another fish family are "talking" among themselves. By the way, the zooportal jokingly disassembled the fish by color:
The aquarist cannot "answer" the fish in their language, but in sioah he can recognize some of the signals given by the fish. This will allow predicting the actions of underwater inhabitants, for example, to notice the approaching spawning, or the growing conflict.
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The morphological side of the coloration of fish has been described earlier. Here we will analyze the ecological significance of color in general and its adaptive significance.
Few animals, not excluding insects and birds, can compete with fish in the brightness and variability of their coloration, which disappears for the most part with death and after being placed in a preservative liquid. Only bony fish (Teleostei) are so diversely colored, which have all the methods of color formation in various combinations. Stripes, spots, ribbons are combined on the main background, sometimes in a very complex pattern.
In the coloration of fish, as well as other animals, many see in all cases an adaptive phenomenon, which is the result of selection and gives the animal the opportunity to become invisible, hide from the enemy, and lie in wait for prey. In many cases this is certainly true, but not always. Recently, there are more and more objections to such a one-sided interpretation of the color of fish. A number of facts speak for the fact that coloration is a physiological result, on the one hand, of metabolism, on the other, of the action of light rays. Coloration arises from this interaction and may have no protective value at all. But in those cases where coloration can be ecologically important, when coloration is supplemented by the corresponding habits of the fish, when it has enemies from which it is necessary to hide (and this is not always the case in those animals that we consider to be patronizingly colored), then coloration becomes a tool in the struggle for existence, is subject to selection and becomes an adaptive phenomenon. Coloring can be useful or harmful not in itself, but being correlated with some other useful or harmful feature.
In tropical waters, both metabolism and light are more intense. And the coloring of animals is brighter here. In the colder and less brightly illuminated waters of the north, and even more so in caves or underwater depths, the color is much less bright, sometimes even scooping.
The need for light in the production of pigment in the skin of fish is supported by experiments with flounders kept in aquariums in which the underside of the flounder was exposed to light. On the latter, a pigment gradually developed, but usually the underside of the body of the flounder is white. Experiments were made with young flounders. Pigmentation developed the same as on the upper side; if the flounders were kept in this way for a long time (1-3 years), then the underside became exactly the same pigmented as the top. This experiment, however, does not contradict the role of selection in the development of protective coloration - it only shows the material from which, due to selection, the flounder has developed the ability to respond to the action of light by forming a pigment. Since this ability could be expressed to the same extent in different individuals, selection could act here. As a result, in flounders (Pleuronoctidae) we see a pronounced changeable protective coloration. In many flounders, the upper surface of the body is colored in various shades of brown with black and light spots and is in harmony with the predominant tone of the sandbars on which they usually feed. Once on the ground of a different color, they immediately change their color to the color corresponding to the color of the bottom. Experiments with the transfer of flounders to soils painted like a chessboard with squares of various sizes gave a striking picture of the animal acquiring the same pattern. It is very important that some fish, which change their habitat at different times in their lives, adapt their coloration to new conditions. For example, Pleuronectes platessa in the summer months rests on clean light sand and is light in color. In the spring, after spawning, R. platessa, having changed color, is looking for silty soil. The same choice of habitat corresponding to coloration, more precisely, the appearance of a different coloration in connection with a new habitat, is also observed in other fish.
Fish living in transparent rivers and lakes, as well as fish in the surface layers of the sea, have a common type of coloration: their back is colored dark, mostly blue, and the ventral side is silvery. It is generally accepted that the dark blue color of the spoke makes the fish invisible to aerial enemies; the lower one - silvery - against predators, who usually stay at a greater depth and can notice the fish from below. Some believe that the silvery-shiny coloration of the belly of fish from below is invisible. According to one opinion, rays reaching the surface of the water from below at an angle of 48° (in salt water 45°) are entirely reflected from the dog. The position of the eyes on the fish's head is such that they can see the surface of the water at a maximum angle of 45°. Thus, only reflected rays enter the eyes of the fish, and the surface of the water appears to the fish as silver-shiny, like the underside and sides of their prey, which for this reason becomes invisible. According to another opinion, the mirror surface of the water reflects the bluish, greenish and brown tops of the entire reservoir, the silvery belly of the fish does the same. The result is the same as in the first case.
However, other researchers believe that the above interpretation of the white or silver color of the belly is incorrect; that its useful value for fish is not proved by anything; that the fish is not attacked from below and that it must appear dark and conspicuous from below. The white color of the ventral side, in this opinion, is a simple consequence of the absence of its illumination. However, a trait can become a species trait only if it is directly or indirectly useful biologically. Therefore, simplified physical explanations are hardly justified.
In fish living at the bottom of the reservoir, the upper surface of the body is dark, often decorated with sinuous stripes, larger or smaller spots. The ventral side is gray or whitish. Such bottom fish include palima (Lota lota), minnow (Gobio fluviatilis), goby (Cottus gobio), catfish (Siluris glanis), loach (Misgurnus fossilis) - from freshwater, sturgeon (Acipenseridae), and from purely marine - marine devil (Lophius piscatorius), stingrays (Batoidei) and many others, especially flounders (Pleuronectidae). In the latter, we see a sharply pronounced changeable protective coloration, which was mentioned above.
We see another type of color variability in cases where fish of the same species become darker in deep water with a muddy or peaty bottom (lake) and lighter in shallow and clear water. An example is the trout (Salmo trutta morpha fario). Trout from gravel or sandy bottom streams are lighter in color than those from muddy streams. Vision is necessary for this color change. We are convinced of this by experiments with transection of the optic nerves.
A striking example of a protective coloration is the Australian species of seahorse - Phyllopteryx eques, in which the skin forms numerous, long, flat, branched threads, colored with brown and orange stripes, like the algae among which the fish lives. Many fish that live among the coral reefs of the Indian and Pacific Oceans, especially fish belonging to the families Ochastodontidae and Pomacentridae, are highly brilliant and lively in color, often decorated with stripes of various colors. In both named families, the same color pattern developed independently. Even the reef-visiting flounders, which are usually dull in color, have the upper surface adorned with lively tops and striking patterning.
Coloring can be not only protective, but also help the predator to be invisible to its prey. Such, for example, is the striped coloration of our perch and pike, and perhaps zander; dark vertical stripes on the body of these fish make them invisible among plants, where they wait for prey. In connection with this coloration, many predators develop special processes on the body that serve to lure prey. Such, for example, is the sea devil (Lophius piscatorius), colored patronizingly and having the anterior ray of the dorsal fin changed into a antennae, movable thanks to special muscles. The movement of this antenna deceives the small fishes, mistaking it for a worm and approaching to disappear into the mouth of Lophius.
It is quite possible that some cases of bright coloration serve as warning coloration in fish. Such, probably, is the brilliant coloration of many symtognathic (Plectognathi). It is associated with the presence of prickly spines that can bulge, and can serve as an indication of the danger of attacking such fish. The significance of the warning coloration, perhaps, is the bright coloring of the sea dragon (Trachinus draco), armed with poisonous spikes on the gill cover and a large spike on the back. Some cases of the complete disappearance of color in fish should perhaps also be attributed to the phenomena of an adaptive nature. Many pelagic larvae of Teleostei lack chromatophores and are colorless. Their body is transparent, and therefore hardly noticeable, just as glass lowered into the water is hardly noticed. Transparency increases due to the absence of hemoglobin in the blood, as, for example, in Leptocephali - eel larvae. Larvae of Onos (family Gadidae) during the pelagic period of their life have a silver color due to the presence of iridocytes in the skin. Ho, passing with age to life under stones, they lose their silver luster and acquire a dark color.
Fish coloring
The color of the fish is very diverse. Small (8–10 centimeters), smelt-like noodle fish with a colorless, completely transparent body lives in the Far Eastern waters: the insides shine through the thin skin. Near the seashore, where the water so often foams, the herds of this fish are invisible. Seagulls manage to eat "noodles" only when the fish jump out and appear above the water. But the same whitish coastal waves that protect the fish from birds often destroy them: on the shores you can sometimes see whole shafts of fish noodles thrown out by the sea. It is believed that after the first spawning, this fish dies. This phenomenon is characteristic of some fish. So cruel nature! The sea throws out both living and “noodles” that died of natural death.
Since fish noodles are usually found in large herds, they should have been used; in part, it is still mined.
There are other fish with a transparent body, for example, the deep-sea Baikal golomyanka, which we will discuss in more detail below.
At the far eastern tip of Asia, in the lakes of the Chukchi Peninsula, there is a black dallium fish.
Its length is up to 20 centimeters. The black coloration makes the fish unobtrusive. Dallium lives in peaty dark-water rivers, lakes and swamps, buries itself in wet moss and grass for the winter. Outwardly, dallium is similar to ordinary fish, but it differs from them in that its bones are delicate, thin, and some are completely absent (there are no infraorbital bones). But this fish has strongly developed pectoral fins. Do not fins such as shoulder blades help fish burrow into the soft bottom of the reservoir in order to survive in the winter cold?
Brook trout are colored with black, blue and red spots of various sizes. If you look closely, you can see that the trout changes its clothes: during the spawning period, it is dressed in a particularly flowery “dress”, at other times - in more modest clothes.
The small minnow fish, which can be found in almost every cool stream and lake, has an unusually variegated color: the back is greenish, the sides are yellow with gold and silver reflections, the abdomen is red, yellowish fins are with a dark rim. In a word, the minnow is small in stature, but he has a lot of force. Apparently, for this he was nicknamed "buffoon", and such a name is perhaps more fair than "minnow", since the minnow is not at all naked, but has scales.
The most brightly colored fish are marine, especially tropical waters. Many of them can successfully compete with birds of paradise. Look at table 1. There are no flowers here! Red, ruby, turquoise, black velvet... They are surprisingly harmoniously combined with each other. Curly, as if honed by skilled craftsmen, the fins and body of some fish are decorated with geometrically regular stripes.
In nature, among corals and sea lilies, these colorful fish are a fabulous picture. Here is what the famous Swiss scientist Keller writes about tropical fish in his book Life of the Sea: “The fish of the coral reefs are the most elegant sight. Their colors are not inferior in brightness and brilliance to the color of tropical butterflies and birds. Azure, yellowish green, velvety black and striped fish flicker and curl in crowds. You involuntarily take hold of the net to catch them, but... one blink of an eye - and they all disappear. With a laterally compressed body, they can easily penetrate the cracks and crevices of coral reefs.
The well-known pikes and perches have greenish stripes on their bodies, which mask these predators in the grassy thickets of rivers and lakes and help them approach their prey unnoticed. But the pursued fish (bleak, roach, etc.) also have a protective coloration: the white belly makes them almost invisible when viewed from below, the dark back is not striking when viewed from above.
Fish living in the upper layers of the water have a more silvery color. Deeper than 100–500 meters, there are fish of red (sea bass), pink (liparis) and dark brown (pinagora) colors. At depths exceeding 1000 meters, the fish are predominantly dark in color (anglerfish). In the area of ocean depths, more than 1700 meters, the color of fish is black, blue, purple.
Table 1. tropical water fish
The color of the fish largely depends on the color of the water and the bottom.
In clear waters, the bersh, which is usually gray in color, is distinguished by whiteness. Against this background, dark transverse stripes stand out especially sharply. In shallow swampy lakes, perch is black, and in rivers flowing from peat bogs, blue and yellow perch are found.
Volkhov whitefish, which once lived in large numbers in the Volkhov Bay and the Volkhov River, which flows through limestone, differs from all Ladoga whitefish in light scales. According to it, this whitefish is easy to find in the total catch of Ladoga whitefish. Among the whitefish of the northern half of Lake Ladoga, black whitefish are distinguished (in Finnish it is called “musta siyka”, which means black whitefish in translation).
The black color of the northern Ladoga whitefish, like the light Volkhov one, remains quite stable: the black whitefish, finding itself in southern Ladoga, does not lose its color. But over time, after many generations, the descendants of this whitefish, who remained to live in southern Ladoga, will lose their black color. Therefore, this feature may vary depending on the color of the water.
After low tide, the flounder remaining in the coastal gray mud is almost completely invisible: the gray color of its back merges with the color of the silt. The flounder acquired such a protective coloration not at the moment when it found itself on a dirty shore, but was inherited from its near and distant ancestors. But fish are capable of changing color very quickly. Put a minnow or other brightly colored fish in a black-bottomed tank and after a while you will see that the color of the fish has faded.
There are many surprising things in the coloring of fish. Among the fish that live at depths where even a weak ray of the sun does not penetrate, there are brightly colored ones.
It also happens like this: in a flock of fish with a color common to a given species, individuals of white or black color come across; in the first case, the so-called albinism is observed, in the second - melanism.
The color of the fish is very diverse. Small (8-10 centimeters *), smelt-like noodle fish with a colorless, completely transparent body lives in the Far Eastern waters: the insides shine through the thin skin. Near the seashore, where the water so often foams, the herds of this fish are invisible. Seagulls manage to eat "noodles" only when the fish jump out and appear above the water. But the same whitish coastal waves that protect the fish from birds often destroy them: on the shores you can sometimes see whole shafts of fish noodles thrown out by the sea. It is believed that after the first spawning, this fish dies. This phenomenon is characteristic of some fish. So cruel nature! The sea throws out both living and natural death "noodles".
* (In the text and under the figures, the largest sizes of fish are given.)
Since fish noodles are usually found in large herds, they should have been used; in part, it is still mined.
There are other fish with a transparent body, for example, the deep-sea Baikal golomyanka, which we will discuss in more detail below.
At the far eastern tip of Asia, in the lakes of the Chukchi Peninsula, there is a black dallium fish.
Its length is up to 20 centimeters. The black coloration makes the fish unobtrusive. Dallium lives in peaty dark-water rivers, lakes and swamps, buries itself in wet moss and grass for the winter. Outwardly, dallium is similar to ordinary fish, but it differs from them in that its bones are delicate, thin, and some are completely absent (there are no infraorbital bones). But this fish has strongly developed pectoral fins. Do not fins such as shoulder blades help fish burrow into the soft bottom of the reservoir in order to survive in the winter cold?
Brook trout are colored with black, blue and red spots of various sizes. If you look closely, you can see that the trout changes its clothes: during the spawning period, it is dressed in a particularly flowery "dress", at other times - in more modest clothes.
A small minnow fish, which can be found in almost every cool stream and lake, has an unusually variegated color: the back is greenish, the sides are yellow with gold and silver reflections, the abdomen is red, yellowish fins are with a dark rim. In a word, the minnow is small in stature, but he has a lot of force. Apparently, for this he was nicknamed "buffoon", and such a name is perhaps more just than "minnow", since the minnow is not at all naked, but has scales.
The most brightly colored fish are marine, especially tropical waters. Many of them can successfully compete with birds of paradise. Look at table 1. There are no flowers here! Red, ruby, turquoise, black velvet ... They are surprisingly harmoniously combined with each other. Curly, as if honed by skilled craftsmen, the fins and body of some fish are decorated with geometrically regular stripes.
In nature, among corals and sea lilies, these colorful fish are a fabulous picture. Here is what the famous Swiss scientist Keller writes about tropical fish in his book "Life of the Sea": "The coral reef fish represent the most elegant sight. Their colors are not inferior in brightness and brilliance to the color of tropical butterflies and birds. Azure, yellowish green, velvety black and striped fish flicker and curl in crowds. You involuntarily take hold of the net to catch them, but .., one blink of an eye - and they all disappear. Possessing a body compressed from the sides, they can easily penetrate into the cracks and crevices of coral reefs. "
The well-known pikes and perches have greenish stripes on their bodies, which mask these predators in the grassy thickets of rivers and lakes and help them approach their prey unnoticed. But the pursued fish (bleak, roach, etc.) also have a protective coloration: the white belly makes them almost invisible when viewed from below, the dark back is not striking when viewed from above.
Fish living in the upper layers of the water have a more silvery color. Deeper than 100-500 meters there are fish of red (sea perch), pink (liparis) and dark brown (pinagora) colors. At depths exceeding 1000 meters, the fish are predominantly dark in color (anglerfish). In the area of ocean depths, more than 1700 meters, the color of fish is black, blue, purple.
The color of the fish largely depends on the color of the water and the bottom.
In transparent WATERS, the bersh, which is usually gray in color, is distinguished by whiteness. Against this background, dark transverse stripes stand out especially sharply. In shallow swampy lakes, perch is black, and in rivers flowing from peat bogs, blue and yellow perch are found.
Volkhov whitefish, which once lived in large numbers in the Volkhov Bay and the Volkhov River, which flows through limestone, differs from all Ladoga whitefish in light scales. According to it, this whitefish is easy to find in the total catch of Ladoga whitefish. Among the whitefish of the northern half of Lake Ladoga, black whitefish are distinguished (in Finnish it is called "musta siyka", which means black whitefish in translation).
The black color of the northern Ladoga whitefish, like the light Volkhov one, remains quite stable: the black whitefish, finding itself in southern Ladoga, does not lose its color. But over time, after many generations, the descendants of this whitefish, who remained to live in southern Ladoga, will lose their black color. Therefore, this feature may vary depending on the color of the water.
After low tide, the flounder remaining in the coastal gray mud is almost completely invisible: the gray color of its back merges with the color of the silt. The flounder did not acquire such a protective coloration at the moment when it found itself on a dirty shore, but received it by inheritance from its neighbors; and distant ancestors. But fish are capable of changing color very quickly. Put a minnow or other brightly colored fish in a black-bottomed tank and after a while you will see that the color of the fish has faded.
There are many surprising things in the coloring of fish. Among the fish that live at depths where even a weak ray of the sun does not penetrate, there are brightly colored ones.
It also happens like this: in a flock of fish with a color common to a given species, individuals of white or black color come across; in the first case, so-called albinism is observed, in the second - melanism.