Coloring of fish, its biological significance. Skin pigmentation and coloration of fish Day and night coloration
The morphological aspect of fish coloration has been described previously. Here we will analyze ecological significance coloring in general and its adaptive significance.
Few animals, not excluding insects and birds, can compete with fish in the brightness and variability of their color, which mostly disappears with death and after being placed in a preservative liquid. Only bony fish (Teleostei) have such a variety of colors, which have all the ways of producing color in various combinations. Stripes, spots, ribbons are combined on the main background, sometimes into a very complex pattern.
In the coloring of fish, like 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 undoubtedly true, but not always. IN Lately There are more and more objections to such a one-sided interpretation of the color of fish. A number of facts suggest that coloring is a physiological result, on the one hand, of metabolism, and on the other, the action of light rays. The coloring occurs due to this interaction and may have no protective value at all. But in cases where coloring can be important ecologically, when coloring is complemented by the corresponding habits of the fish, when it has enemies from which it must hide (and this is not always the case in those animals that we consider protectively colored), then coloring becomes a tool in the struggle for existence, is subject to selection and becomes an adaptive phenomenon. Color can be beneficial or harmful not in itself, but when associated correlatively with some other useful or harmful feature.
IN tropical waters ah and metabolism and light are more intense. And the colors of the animals here are brighter. In the colder and less brightly lit waters of the north, and even more so in caves or underwater depths, the color is much less bright, sometimes even scooping.
The necessity of light for the production of pigment in the skin of fish is evidenced by experiments with flounder kept in aquariums in which the underside of the flounder was exposed to light. The latter gradually developed pigment; usually the underside of the flounder’s body is white. Experiments were done with young flounders. The pigmentation developed is the same as on the upper side; if the flounder kept this way for a long time (1-3 years), then the lower side became exactly as pigmented as the upper. This experiment, however, does not contradict the role of selection in the development of protective coloration - it only shows the material from which, thanks to selection, flounders have developed the ability to respond to the action of light by producing 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 pronounced variable protective coloration. Many flounders top surface body is painted in various shades brown in color with black and light spots and harmonizes with the prevailing tone of the sandbanks on which they usually feed. Having landed on soil of a different color, they immediately change their color to a 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 that change their habitat at different times in their lives adapt their color to the new conditions. For example, Pleuronectes platessa in summer months rests on clean light sand and is lightly colored. In the spring, after spawning, P. platessa, having changed color, searches for muddy soil. The same choice of habitat corresponding to color, or more precisely, the appearance of a different color in connection with a new habitat, is also observed in other fish.
Fish living in clear rivers and lakes, as well as fish in the surface layers of the sea, have general type coloration: the back is dark, mostly Blue colour, and the ventral side is silver in tone. It is generally accepted that the dark blue color of the spoke makes the fish invisible to aerial enemies; the lower one - silver - against predators, which usually stay at greater depths and can notice the fish from below. Some believe that the silvery-shiny coloring of the fish's belly underneath is invisible. According to one opinion, rays reaching the surface of the water from below at an angle of 48° (45° in salt water) are entirely reflected from the sand. The position of the eyes on the head of the fish is such that they can see the surface of the water at most at an angle of 45°. Thus, only reflected rays enter the eyes of the fish, and the surface of the water appears to the fish as silvery-shiny, like the lower and sides 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, and 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; what's her useful value nothing has been proven for fish; that the fish is not attacked from below and that it should appear dark and visible from below. The white color of the ventral side, in this opinion, is a simple consequence of the lack of illumination. However, a trait can become a species characteristic only if it is directly or indirectly useful biologically. Therefore simplified physical explanations are unlikely to be justified.
In fish that live at the bottom of a reservoir, the upper surface of the body is dark, often decorated with winding stripes, large or smaller spots. The ventral side is gray or whitish. Such bottom fish include palm (Lota lota), gudgeon (Gobio fluviatilis), goby (Cottus gobio), catfish (Siluris glanis), loach (Misgurnus fossilis) - from freshwater, sturgeon (Acipenseridae), and from purely marine - marine devils (Lophius piscatorius), stingrays (Batoidei) and many others, especially flounders (Pleuronectidae). In the latter we see a pronounced, variable protective coloration, which was mentioned above.
We see another type of color variation in cases where fish of the same species become darker in deep water with a muddy or peaty bottom (lakes) and lighter in shallow and clear water. An example is trout (Salmo trutta morpha fario). Trout from streams with gravel or sandy bottoms are lighter in color than those taken from muddy streams. This color change requires vision. Experiments with transection of the optic nerves convince us of this.
A striking example of protective coloration is the Australian species 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 living among the coral reefs of Indian and Pacific Oceans, especially fish belonging to the families Ohaсtodontidae and Pomacentridae, are highly brilliant and vibrant in color, often decorated with stripes of various colors. In both named families, the same color pattern evolved independently. Even reef-visiting flounder fish, which are usually dull in color, sometimes have lively tops and striking patterns on their upper surfaces.
Coloring can be not only protective, but also help the predator to be invisible to its prey. Such, for example, is the striped color of our perch and pike and, perhaps, pike perch; dark vertical stripes on the body of these fish make them invisible among the plants where they wait for prey. Due to this coloration, many predators develop special processes on their bodies that serve to lure prey. Such, for example, is the sea devil (Lophius piscatorius), which is colored protectively and has the anterior ray of the dorsal fin modified into an antennae, mobile thanks to special muscles. The movement of this antenna deceives small fish, who mistake it for a worm and approach to disappear into the mouth of Lophius.
It is quite possible that some cases of bright coloration serve as warning colors in fish. This is probably the brilliant coloration of many fused-jawed animals (Plectognathi). It is associated with the presence of prickly spines that can bristle, and can serve as an indication of the danger of attack on such fish. The meaning of warning coloring, perhaps, has bright colors sea dragon(Trachinus draco), armed with poisonous spines on operculum And big thorn on the back. Some cases of complete disappearance of color in fish may also be considered adaptive phenomena. Many pelagic Teleostei larvae do not have chromatophores and are colorless. Their body is transparent, and therefore difficult to notice, just as glass lowered into water is difficult to notice. Transparency increases due to the absence of hemoglobin in the blood, as, for example, in Leptocephali - eel larvae. Onos larvae (family Gadidae) have a silver color during the pelagic period of their life, due to the presence of iridocytes in the skin. But, moving with age to life under stones, they lose their silver shine and acquire a dark color.
The coloring of fish is very diverse. IN Far Eastern waters inhabits a small (8-10 centimeters1), smelt-like noodle fish with a colorless, completely transparent body: the insides are visible through the thin skin. Near seashore where the water foams so often, schools of this fish are invisible. The seagulls manage to enjoy the “noodles” only when the fish jump out and appear above the water. But the same whitish coastal waves that serve as protection for fish from birds often destroy them: on the shores you can sometimes see whole banks of noodle fish thrown up by the sea. There is an opinion that after the first spawning this fish dies. This phenomenon is typical for some fish. Nature is so merciless! The sea throws out both living and natural “noodles”.
Since noodle fish are usually found in large schools, they should have been used; Some of it is still being mined. 
There are other fish with a transparent body, for example, deep-sea Baikal golomyanki, which we will talk about in more detail below.
On the far eastern tip of Asia, in the lakes of the Chukotka Peninsula, the black dallium fish is found. Its length is up to 20 centimeters. The black color makes the fish inconspicuous. Dallia lives in dark-water peat rivers, lakes and swamps, and burrows into wet moss and grass for the winter. Externally, dalliya looks like common 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 highly developed pectoral fins. Don't fins like scapulae help fish bury themselves in the soft bottom of a reservoir in order to survive the winter cold? Brook trout are colored with black, blue and red spots of varying sizes. If you look closely, you will notice that the trout changes its attire: 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 belly is red, yellowish fins have a dark edge. In a word, the minnow is small in stature, but it has a lot of force. Apparently, for this he was nicknamed “buffoon”; this name is perhaps more fair than “minnow”, since the minnow is not naked at all, but has scales.
Marine fish are the most brightly colored, especially in tropical waters. Many of them can successfully compete with birds of paradise. There are so many flowers here! Red, ruby, turquoise, black velvet... They combine surprisingly harmoniously with each other. Figured, as if sharpened 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 present a fabulous picture. This is what he writes about tropical fish the famous Swiss scientist Keller in his book “The Life of the Sea”: “The fish of coral reefs present the most elegant spectacle. Their colors are not inferior in brightness and brilliance to the colors of tropical butterflies and birds. Azure, yellowish-green, velvety black and striped fish flickering and curling in whole crowds. You involuntarily take 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 pike and perch have greenish stripes on their bodies that camouflage these predators in the grassy thickets of rivers and lakes and help them approach their prey unnoticed. But the hunted fish (bleak, roach, etc.) also have patronizing connotation: the white belly makes them almost invisible when viewed from below, the dark back is not noticeable when viewed from above.
Fishes living in upper layers water, have a more silvery color. Below 100-500 meters there are red fish ( sea bass), pink (liparis) and dark brown (lumpfish) flowers. At depths exceeding 1000 meters, fish are predominantly dark in color (angler fish). In the area of ocean depths, more than 1700 meters, the color of fish is black, blue, purple.
The color of fish largely depends on the color of the water and bottom.
IN clear waters Bersh, which is usually gray in color, is distinguished by its whiteness. Against this background, the dark transverse stripes stand out especially sharply. In small swampy lakes, perch is black, and in rivers flowing from peat bogs, perch of blue and yellow colors are found.
Volkhov whitefish, which was once in large quantities lived in the Volkhov Bay and the Volkhov River, which flows through limestones, differs from all Ladoga whitefish in having light scales. According to it, this whitefish can be easily found in the general catch of whitefish in Ladoga.
Among the whitefish northern half Lake Ladoga, they distinguish black whitefish (in Finnish it is called “musta siika”, which means “black whitefish”).
The black color of the northern Ladoga whitefish, like the light one of the Volkhov whitefish, remains quite persistent: the black whitefish, once 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 coloring. Therefore, this feature may vary depending on the color of the water.
After low tide, the flounder remaining in the gray coastal mud is almost completely invisible: grey colour her back merges with the color of the mud. The flounder acquired this protective coloring 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. Place a minnow or other brightly colored fish in a black-bottomed aquarium, 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 sun cannot penetrate, there are brightly colored ones.
It also happens: in a school of fish with the usual color for a given species, there are individuals of white or black color; in the first case, so-called albinism is observed, in the second - melanism.
I, Pravdin “A story about the life of fish” V. Sabunaev, “Entertaining ichthyology”
The color of fish can be surprisingly varied, but all possible shades of their color are due to the work of special cells called chromatophores. They are found in a specific layer of the fish's skin and contain several types of pigments. Chromatophores are divided into several types. First, these are melanophores, which contain a black pigment called melanin. Further, ethytrophores, containing red pigment, and xanthophores, in which it is yellow. The latter type is sometimes called lipophores because the carotenoids that make up the pigment in these cells are dissolved in lipids. Guanophores or iridocytes contain guanine, which gives fish a silvery color and a metallic sheen. The pigments contained in chromatophores differ chemically in stability, solubility in water, sensitivity to air and some other characteristics. The chromatophores themselves are also not the same in shape - they can be either star-shaped or round. Many colors in the coloration of fish are obtained by superimposing one chromatophore on another; this possibility is ensured by the occurrence of cells in the skin at different depths. For example, green color is obtained when deep-lying guanophores are combined with covering xanthophores and erythrophores. If you add melanophores, the fish's body turns blue.
Chromatophores do not have nerve endings, with the exception of melanophores. They are even involved in two systems at once, having both sympathetic and parasympathetic innervation. The remaining types of pigment cells are controlled humorally.
The coloring of fish is quite important for their life. The functions of coloring are divided into protective and warning. The first option is designed to camouflage the fish’s body in the environment, so this color usually consists of calm colors. Warning coloring, on the contrary, includes a large number of bright spots and contrasting colors. Its functions are different. In poisonous predators, who usually say with the brightness of their body: “Don’t come near me!”, it plays a deterrent role. Territorial fish, guarding their home, are brightly colored to warn rivals that the site is occupied and to attract a mate. A type of warning coloration is also the mating plumage of fish.
Depending on the habitat, the body color of the fish acquires character traits, allowing to distinguish pelagic, bottom, thicket and schooling colors.
Thus, the color of fish depends on many factors, including habitat, lifestyle and diet, time of year and even the mood of the fish.
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Fish have extremely varied colors with very bizarre patterns. A particular variety of colors is observed in fish of tropical and warm waters. It is known that fish of the same species in different bodies of water have different colors, although they mainly retain the pattern characteristic of this species. Take pike, for example: its color varies from dark green to bright yellow color. Perch usually has bright red fins, a greenish color on the sides and a dark back, but there are whitish perches (in rivers) and, conversely, dark ones (in ilmen). All such observations indicate that the color of fish depends on their systematic position from the habitat, environmental factors, nutritional conditions.
The color of fish is determined by special cells, lying in the skin containing pigment grains. Such cells are called chromatophores.
They are distinguished: melanophores (contain black pigment grains), erythrophores (red), xanthophores (yellow) and guanophores, iridocytes (silver color).
Although the latter are classified as chromatophores and do not have pigment grains, they do contain crystalline substance- guanine, due to which the fish acquires a metallic sheen and silvery color. Of the chromatophores, only melanophores have nerve endings. The shape of chromatophores varies greatly, however, the most common are star-shaped and disc-shaped.
In terms of chemical resistance, the black pigment (melanin) is the most resistant. It is not soluble in acids or alkalis, and does not change as a result of changes in the physiological state of the fish (starvation, nutrition). Red and yellow pigments are associated with fats, so the cells containing them are called lipophores. The pigments of erythrophores and xanthophores are very unstable, dissolve in alcohols and depend on the quality of nutrition.
Chemically, pigments are complex substances belonging to different classes:
1) carotenoids (red, yellow, orange)
2) melanins - indoles (black, brown, gray)
3) flavins and purine groups.
Melanophores and lipophores are located in different layers of the skin on the outer and inner sides boundary layer (cutis). Guanophores (or leucophores, or iridocytes) differ from chromatophores in that they do not have pigment. Their color is due to the crystal structure of guanine, a protein derivative. Guanophores are located under the chorium. It is very important that guanine is located in the cell plasma, like pigment grains, and its concentration can change due to intracellular plasma currents (thickening, liquefaction). Guanine crystals have a hexagonal shape and, depending on their location in the cell, the color varies from silvery-whitish to bluish-violet.
Guanophores are in many cases found together with melanophores and erythrophores. They play very big biological role in the life of fish, because being located on the ventral surface and on the sides they make the fish less noticeable from below and from the sides; The protective role of coloring appears especially clearly here.
The function of pigment staves is mainly expansion, i.e. occupying more space (expansion) and reducing i.e. occupying the smallest space (contraction). When the plasma contracts, decreasing in volume, the pigment grains in the plasma become concentrated. Thanks to this most of The cell surface is freed from this pigment and as a result, the brightness of the color decreases. During expansion, the cell plasma spreads over a larger surface, and pigment grains are distributed along with it. Due to this, a large surface of the fish’s body is covered with this pigment, giving the fish a color characteristic of the pigment.
The reason for the expansion of the concentration of pigment cells can be both internal factors (physiological state of the cell, organism), and some factors external environment(temperature, oxygen and carbon dioxide content in the input). Melanophores have innervation. In canthophores and erythrophores there is no innervation: Consequently, the nervous system can have a direct influence only on melanophores.
It has been established that pigment cells bony fish maintain a constant shape. Koltsov believes that the plasma of a pigment cell has two layers: ectoplasm (surface layer) and cinemaplasm (inner layer), containing pigment grains. Ectoplasm is fixed by radial fibrils, and cinemaplasm is very mobile. Ectoplasm determines external form chromatophore (a form of ordered movement), regulates metabolism, changes its function under the influence of the nervous system. Ectoplasm and cinemaplasm, having different physicochemical characteristics, mutual wettability when their properties change under the influence of the external environment. During expansion (expansion), cinema plasma well wets the ectoplasm and, thanks to this, spreads over the cracks covered with ectoplasm. The pigment grains are in the cinema plasma, are well moistened by it and follow the flow of the cinema plasma. With concentration, the opposite picture is observed. The separation of two colloidal layers of protoplasm occurs. Cinematic plasma does not wet ectoplasm and, thanks to this, cinematic plasma
occupies the smallest volume. At the heart of this process is change surface tension at the border of two layers of protoplasm. Ectoplasm by its nature is a protein solution, and cinema plasma is a lipoid like lecithin. Kinoplasma is emulsified (very finely crushed) in ectoplasm.
In addition to nervous regulation, chromatophores also have hormonal regulation. It must be assumed that when different conditions some kind of regulation is carried out. Amazing adaptation of body coloration to color environment observed in pipefish, gobies, flounder. Flounders, for example, can copy the pattern of the ground and even a chessboard with great accuracy. This phenomenon is explained by the fact that the nervous system plays a leading role in this adaptation. The fish perceives color through the organ of vision and then, transforming this perception, the nervous system controls the function of pigment cells.
In other cases, hormonal regulation is clearly evident (coloring during the breeding season). The blood of fish contains hormones from the adrenal gland - adrenaline and the posterior lobe of the pituitary gland - pituitrin. Adrenaline causes concentration, pituitrin is an adrenaline antagonist and causes expansion (dispersal).
Thus, the function of pigment cells is under the control of the nervous system and hormonal factors, i.e. internal factors. But besides them, environmental factors (temperature, carbon dioxide, oxygen, etc.). The time required for fish to change color varies and ranges from a few seconds to several days. As a rule, young fish change their color faster than adults.
It is known that fish change body color according to the color of their environment. Such copying is carried out only if the fish can see the color and pattern of the soil. The following example illustrates this. If a flounder lies on a black board but does not see it, then it is colored not by the black board, but by the white ground visible to it. On the contrary, if a flounder lies on white ground, but sees a black board, then its body takes on the color of a black board. These experiments convincingly show that fish easily adapt, changing their color to soil that is unusual for them.
The color of the fish is influenced by light. “So in dark places where there is low light, fish lose color. Bright fish, having lived for some time in the dark, become pale in color. Blinded fish acquire dark color. On dark the fish becomes dark in color, on light it becomes light. Frisch was able to establish that the darkening and lightening of the fish’s body depends not only on the illumination of the ground, but also on the viewing angle from which the fish can see the ground. So, if the eyes of a trout are blindfolded or removed, the fish turns black. If you cover only the lower half of the eye, the fish acquires a dark color, and if you cover only the upper half of the eye, the fish retains its color.
Light has the most powerful and varied effect on the color of fish. Light
affects melanophores both through the eyes and nervous system, and directly. So Frisch, by illuminating individual areas of the fish’s skin, received a local change in color: a darkening of the illuminated area was observed (expansion of melanophores), which disappeared 1-2 minutes after turning off the light. Due to prolonged illumination, the color of the back and abdomen of the fish changes. Typically, the back of fish that live at shallow depths and in clear waters has a dark tone, and the abdomen is light. In fish living at great depths and troubled waters no such difference in color is observed. It is believed that the difference in the color of the back and belly has an adaptive significance: the dark back of the fish is less visible from above against a dark background, and the light belly is less visible from below. In this case, the different colors of the abdomen and back are due to uneven distribution of pigments. There are melanophores on the back and sides, and on the sides there are only iridocytes (tuanophores), which give the abdomen a metallic sheen.
When the skin is locally heated, melanophores expand, leading to darkening; when cooled, it leads to lightening. A decrease in oxygen concentration and an increase in carbonic acid concentration also changes the color of fish. You have probably observed that after death in fish, the part of the body that was in the water has a lighter color (the concentration of melanophores), and the part that protrudes from the water and comes into contact with the air has a dark color (the expansion of melanophores). In fish in in good condition, usually the color is bright and multi-colored. With a sharp decrease in oxygen or in a state of suffocation, the skin becomes paler, dark tones almost completely disappear. But the fading of the color of the fish cover is a result of the concentration of chromatophores and , primarily melanophores. As a result of a lack of oxygen, the surface of the fish's skin is not supplied with oxygen as a result of cessation of blood circulation or poor oxygen supply to the body (the beginning of suffocation), and always acquires a pale tone. An increase in carbon dioxide in water affects the color of fish in the same way as a lack of oxygen. Consequently, these factors (carbon dioxide and oxygen) act directly on the chromatophores, therefore, the center of irritation is located in the cell itself - in the plasma.
The effect of hormones on the color of fish is revealed primarily during mating season(breeding season). Particularly interesting coloring of the skin and fins is observed in males. The function of chromatophores is under the control of hormonal agents and the feather system. Example with betta fish. In this case, mature males, under the influence of hormones, acquire the appropriate coloration, the brightness and brilliance of which intensifies when they see a female. The male's eyes see the female, this perception is transmitted through the nervous system to the chromatophores and causes their expansion. The male's skin chromatophores function in this case under the control of hormones and the nervous system.
Experimental work on minnows has shown that injection of adrenaline causes lightening of the fish's integument (contraction of melanophores). Microscopic examination of the skin of an adrenalized minnow showed that melanophores are in a state of contraction, and lipophores are in expansion.
Self-test questions:
1. Structure and functional significance of fish skin.
2. The mechanism of mucus formation, its composition and significance.
3. Structure and functions of scales.
4. The physiological role of skin and scale regeneration.
5. The role of pigmentation and coloring in the life of fish.
Section 2: Laboratory materials.
Fish coloring
The coloring of fish is very diverse. The Far Eastern waters are inhabited by small (8–10 centimeters), smelt-like noodle fish with a colorless, completely transparent body: the insides are visible through the thin skin. Near the seashore, where the water so often foams, schools of this fish are invisible. The seagulls manage to enjoy the “noodles” only when the fish jump out and appear above the water. But the same whitish coastal waves that serve as protection for fish from birds often destroy them: on the shores you can sometimes see whole banks of noodle fish thrown up by the sea. There is an opinion that after the first spawning this fish dies. This phenomenon is typical for some fish. Nature is so merciless! The sea throws out both living and natural “noodles”.
Since noodle fish are usually found in large schools, they should have been used; Some of it is still being mined.
There are other fish with a transparent body, for example, deep-sea Baikal golomyanki, which we will talk about in more detail below.
On the far eastern tip of Asia, in the lakes of the Chukotka Peninsula, the black dallium fish is found.
Its length is up to 20 centimeters. The black color makes the fish inconspicuous. Dallia lives in dark-water peat rivers, lakes and swamps, and burrows into wet moss and grass for the winter. Externally, dalliya 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 highly developed pectoral fins. Don't fins like scapulae help fish bury themselves in the soft bottom of a reservoir in order to survive the winter cold?
Brook trout are colored with black, blue and red spots of varying sizes. If you look closely, you will notice that the trout changes its attire: 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 belly is red, yellowish fins have a dark edge. In a word, the minnow is small in stature, but it has a lot of force. Apparently, for this he was nicknamed “buffoon”, and this name is perhaps more fair than “minnow”, since the minnow is not naked at all, but has scales.
Marine fish are the most brightly colored, especially in tropical waters. Many of them can successfully compete with birds of paradise. Look at table 1. There are so many colors here! Red, ruby, turquoise, black velvet... They combine surprisingly harmoniously with each other. Figured, as if sharpened 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 present a fabulous picture. Here is what the famous Swiss scientist Keller writes about tropical fish in his book “The Life of the Sea”: “The fish of coral reefs present the most elegant spectacle. Their colors are not inferior in brightness and brilliance to the colors of tropical butterflies and birds. Azure, yellowish-green, velvety black and striped fish flash and curl in droves. You involuntarily take the net to break 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 pike and perch have greenish stripes on their bodies that camouflage these predators in the grassy thickets of rivers and lakes and help them quietly approach their prey. But the pursued fish (bleak, roach, etc.) also have a protective coloring: the white belly makes them almost invisible when viewed from below, the dark back does not catch the eye when viewed from above.
Fish living in the upper layers of water have a more silvery color. Below 100–500 meters there are fish of red (sea bass), pink (liparis) and dark brown (lumpfish) colors. At depths exceeding 1000 meters, fish are predominantly dark in color (angler fish). In the area of ocean depths, more than 1700 meters, the color of fish is black, blue, purple.
Table 1. Fishes of tropical waters
The color of fish largely depends on the color of the water and bottom.
In clear waters, the bersh, which is usually gray in color, is distinguished by its whiteness. Against this background, the dark transverse stripes stand out especially sharply. In small swampy lakes, perch is black, and in rivers flowing from peat bogs, perch of blue and yellow colors are found.
The Volkhov whitefish, which once lived in large numbers in the Volkhov Bay and the Volkhov River, which flows through the limestones, differs from all Ladoga whitefish in having light-colored scales. According to it, this whitefish can be easily found in the general catch of whitefish in Ladoga. Among the whitefish of the northern half of Lake Ladoga, a black whitefish is distinguished (in Finnish it is called “musta siika”, which means black whitefish).
The black color of the northern Ladoga whitefish, like the light one of the Volkhov whitefish, remains quite persistent: the black whitefish, once 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 coloring. Therefore, this feature may vary depending on the color of the water.
After low tide, the flounder remaining in the gray coastal mud is almost completely invisible: the gray color of its back merges with the color of the silt. The flounder acquired this protective coloring 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. Place a minnow or other brightly colored fish in a black-bottomed aquarium, 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 sun cannot penetrate, there are brightly colored ones.
It also happens: in a school of fish with the usual color for a given species, there are individuals of white or black color; in the first case, so-called albinism is observed, in the second - melanism.