What role does the bright coloring of male fish play. What determines the color of fish
Coloration is of great biological importance for fish. There are protective and warning colors. Protective coloring is intended
chena mask the fish on the background environment. Warning, or sematic, coloration usually consists of conspicuous large, contrasting spots or bands that have clear boundaries. It is intended, for example, in poisonous and poisonous fish, to prevent a predator from attacking them, and in this case it is called a deterrent.
Identification coloration is used to warn territorial fish of rivals, or to attract females to males, warning them that males are ready to spawn. The last type of warning coloration is commonly referred to as the mating dress of fish. Often the identification coloration unmasks the fish. It is for this reason that in many fish guarding the territory or their offspring, the identification coloration in the form of a bright red spot is located on the belly, shown to the opponent if necessary, and does not interfere with the masking of the fish when it is located belly to the bottom. There is also a pseudosematic coloration that mimics the warning coloration of another species. It is also called mimicry. It allows harmless species of fish to avoid the attack of a predator that takes them for a dangerous species.
Poison glands.
Some fish species have venom glands. They are located mainly at the base of the spines or spiny rays of the fins (Fig. 6).
There are three types of venom glands in fish:
1. individual cells of the epidermis containing poison (stargazer);
2. a complex of poisonous cells (stingray-stingray);
3. independent multicellular poisonous gland (wart).
The physiological effect of the released poison is not the same. In the stingray, the poison causes severe pain, severe swelling, chills, nausea and vomiting, in some cases death occurs. The poison of the wart destroys red blood cells, affects the nervous system and leads to paralysis, if the poison enters the bloodstream, it leads to death.
Sometimes poisonous cells are formed and function only during reproduction, in other cases - constantly. Fish are divided into:
1) actively poisonous (or poisonous, having a specialized poisonous apparatus);
2) passively poisonous (having poisonous organs and tissues). The most poisonous are fish from the pufferfish order, in which the internal organs (gonads, liver, intestines) and skin contain the poison neurotoxin (tetrodotoxin). The poison acts on the respiratory and vasomotor centers, withstands boiling for 4 hours and can cause rapid death.
Poisonous and poisonous fish.
Fish with poisonous properties are divided into poisonous and poisonous. Poisonous fish have a venomous apparatus - spikes and poisonous glands located at the base of the spikes (for example, in sea scorpion
(Eurapean kerchak) during spawning) or in the grooves of spikes and fin rays (Scorpaena, Frachinus, Amiurus, Sebastes, etc.). The strength of the action of poisons is different - from the formation of an abscess at the injection site to respiratory and cardiac disorders and death (in severe cases of Trachurus infection). When eaten, these fish are harmless. Fish whose tissues and organs are poisonous chemical composition, are poisonous and should not be eaten. They are especially numerous in the tropics. The liver of the shark Carcharinus glaucus is poisonous, while the puffer Tetrodon has poisonous ovaries and eggs. In our fauna, in the marinka Schizothorax and the osman Diptychus, caviar and peritoneum are poisonous, in the barbel Barbus and the templar Varicorhynus, the caviar has a laxative effect. The poison of poisonous fish acts on the respiratory and vasomotor centers, and is not destroyed by boiling. Some fish have poisonous blood (eels Muraena, Anguilla, Conger, as well as lamprey, tench, tuna, carp, etc.)
Poisonous properties are shown at an injection of blood serum of these fishes; they disappear when heated under the action of acids and alkalis. Poisoning with stale fish is associated with the appearance in it of poisonous waste products of putrefactive bacteria. Specific "fish poison" is formed in benign fish (mainly sturgeon and white salmon) as a product of the vital activity of anaerobic bacteria Bacillus ichthyismi (close to B. botulinus). The action of the poison is manifested by the use of raw (including salted) fish.
Luminous organs of fish.
The ability to emit cold light is widespread in various, unrelated groups of marine fish (in most deep-sea ones). This is a glow of a special kind, in which light emission (in contrast to the usual - arising from thermal radiation - based on the thermal excitation of electrons and therefore accompanied by the release of heat) is associated with the generation of cold light (the necessary energy is generated as a result of chemical reaction). Some species generate light themselves, while others owe their glow to symbiotic luminous bacteria that are on the surface of the body or in special organs.
The device of the organs of luminescence and their location in different aquatic inhabitants are different and serve different purposes. Glow is usually provided by special glands located in the epidermis or on certain scales. The glands are made up of luminous cells. Pisces are able to arbitrarily “turn on” and “turn off” their glow. The location of the luminous organs is different. In most deep-sea fish, they are collected in groups and rows on the sides, belly and head.
The luminous organs help to find individuals of the same species in the dark (for example, in schooling fish), serve as a means of protection - they suddenly illuminate the enemy or throw out a luminous curtain, thus driving away the attackers and hiding from them under the protection of this luminous cloud. Many predators use the glow as a light bait, attracting them in the dark to fish and other organisms that they feed on. So, for example, some species of shallow-sea young sharks have various luminous organs, and the Greenland shark's eyes glow like bright lanterns. The greenish phosphoric light emitted by these organs attracts fish and other sea creatures.
Sense organs of fish.
The organ of vision - the eye - in its structure resembles a photographic apparatus, and the lens of the eye is like a lens, and the retina is like a film on which an image is obtained. In land animals, the lens has a lenticular shape and is able to change its curvature, so animals can adjust their vision to distance. The lens of fish is spherical and cannot change shape. Their vision is rebuilt at different distances when the lens approaches or moves away from the retina.
The organ of hearing - is presented only ext. ear, consisting of a labyrinth filled with liquid, in a cut auditory pebbles (otoliths) float. Their vibrations are perceived by the auditory nerve, which transmits signals to the brain. The otoliths also serve as an organ of balance for the fish. A lateral line runs along the body of most fish - an organ that perceives low-frequency sounds and the movement of water.
The olfactory organ is located in the nostrils, which are simple pits with a mucous membrane penetrated by a branching of the nerves coming from the smell. parts of the brain. Sense of smell aquarium fish very well developed and helps them in finding food.
Taste organs - represented by taste buds oral cavity, on the antennae, on the head, on the sides of the body and on the rays of the fins; help fish determine the type and quality of food.
The organs of touch are especially well developed in fish that live near the bottom, and are groups of senses. cells located on the lips, the end of the snout, fins and special. palpation organs (dec. antennae, fleshy outgrowths).
Swim bladder.
Fish buoyancy (the ratio of fish body density to water density) can be neutral (0), positive or negative. In most species, buoyancy ranges from +0.03 to -0.03. With positive buoyancy, the fish float up, with neutral buoyancy they float in the water column, with negative buoyancy they sink.
Neutral buoyancy (or hydrostatic balance) in fish is achieved:
1) with the help of a swim bladder;
2) watering the muscles and lightening the skeleton (in deep-sea fish)
3) accumulation of fat (sharks, tuna, mackerels, flounders, gobies, loaches, etc.).
Most fish have a swim bladder. Its occurrence is associated with the appearance of a bone skeleton, which increases the proportion of bony fish. In cartilaginous fish, there is no swim bladder; among bony fish, it is absent in bottom fish (gobies, flounders, lumpfish), deep-sea and some fast-swimming species (tuna, bonito, mackerel). An additional hydrostatic adaptation in these fish is the lifting force, which is formed due to muscular efforts.
The swim bladder is formed as a result of protrusion of the dorsal wall of the esophagus, its main function is hydrostatic. The swim bladder also perceives changes in pressure, is directly related to the organ of hearing, being a resonator and reflector of sound vibrations. In loaches, the swim bladder is covered with a bone capsule, has lost its hydrostatic function, and has acquired the ability to perceive changes in atmospheric pressure. In lungfish and bony ganoids, the swim bladder performs the function of respiration. Some fish are able to make sounds with the help of a swim bladder (cod, hake).
The swim bladder is a relatively large elastic sac that is located under the kidneys. It happens:
1) unpaired (most fish);
2) paired (lungfish and multi-feathered).
Many secrets and mysteries of nature still remain unsolved, but every year scientists discover more and more new species of previously unknown animals and plants.
Thus, snail worms were recently discovered, whose ancestors lived on Earth over 500 million years ago; scientists also managed to catch a fish that was previously thought to have died out 70 million years ago.
This material is dedicated to the extraordinary, mysterious and so far inexplicable phenomena of ocean life. Learn to understand the complex and varied relationships between the inhabitants of the ocean, many of which have lived in its depths for millions of years.
Lesson type: Generalization and systematization of knowledge
Target: development of erudition, cognitive and creativity students; formation of the ability to search for information to answer the questions posed.
Tasks:
Educational: shaping cognitive culture, mastered in the process of educational activity, and aesthetic culture as the ability to have an emotional and valuable attitude towards objects of wildlife.
Developing: development of cognitive motives aimed at obtaining new knowledge about wildlife; cognitive qualities of the individual associated with the assimilation of the basics scientific knowledge, mastering the methods of studying nature, the formation of intellectual skills;
Educational: orientation in the system of moral norms and values: recognition high value life in all its manifestations, health of one's own and other people; ecological consciousness; education of love for nature;
Personal: understanding of responsibility for the quality of acquired knowledge; understanding the value of an adequate assessment of one's own achievements and capabilities;
cognitive: the ability to analyze and evaluate the impact of environmental factors, risk factors on health, the consequences of human activities in ecosystems, the impact of one's own actions on living organisms and ecosystems; focus on continuous development and self-development; the ability to work with various sources of information, convert it from one form to another, compare and analyze information, draw conclusions, prepare messages and presentations.
Regulatory: the ability to organize independently the execution of tasks, evaluate the correctness of the work, reflection of their activities.
Communicative: the formation of communicative competence in communication and cooperation with peers, understanding the characteristics of gender socialization in adolescence, socially useful, educational, research, creative and other activities.
Technology: Health saving, problematic, developmental education, group activities
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Conversation - reasoning about previously acquired knowledge on a given topic,
Watching video (movie),
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« What determines the color of fish?
Presentation "What determines the color of fish"
The inhabitants of the sea are among the most brightly colored creatures in the world. Such organisms, shimmering with all the colors of the rainbow, live in the sun-drenched waters of warm tropical seas.
Coloration of fish, its biological significance.
Coloration is of great biological importance for fish. There are protective and warning colors. The protective coloration is intended to camouflage the fish against the background of the environment. Warning, or sematic, coloration usually consists of conspicuous large, contrasting spots or bands that have clear boundaries. It is intended, for example, in poisonous and poisonous fish, to prevent a predator from attacking them, and in this case it is called a deterrent.
Identification coloration used to warn a rival in territorial fish, or to attract females to males by warning them that the males are ready to spawn. The last type of warning coloration is commonly referred to as the mating dress of fish. Often the identification coloration unmasks the fish. It is for this reason that in many fish guarding the territory or their offspring, the identification coloration in the form of a bright red spot is located on the belly, shown to the opponent if necessary, and does not interfere with the masking of the fish when it is located belly to the bottom. There is also a pseudosematic coloration that mimics the warning coloration of another species. It is also called mimicry. It allows harmless species of fish to avoid the attack of a predator that takes them for a dangerous species.
What determines the color of fish?
The color of fish can be surprisingly diverse, 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 containing a black pigment called melanin. Further, etitrophores, 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 the color of fish a silvery color and metallic luster. The pigments contained in chromatophores differ chemically in terms of stability, solubility in water, sensitivity to air, and some other features. The chromatophores themselves are also not the same in shape - they can be either stellate or rounded. Many colors in the coloration of fish are obtained by superimposing some chromatophores on others, this possibility is provided by the occurrence of cells in the skin at different depths. For example, green color is obtained when deep-lying guanophores are combined with xanthophores and erythrophores covering them. If you add melanophores, the body of the fish acquires blue color.
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. Other types of pigment cells are controlled humorally.
The color of fish is quite important for their life.. Coloring functions are divided into patronizing and warning. The first option is designed to mask the body of the fish in the environment, so usually this coloration consists of soothing colors. Warning coloring, on the contrary, includes a large number of bright spots and contrasting colors. Its functions are different. In poisonous predators, which 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 in order to warn the rival that the place is occupied and to attract the female. A kind of warning coloration is also the marriage attire 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 nutrition, season, and even the mood of the fish.
Identification coloration
In the waters around the coral reefs, which are teeming with all sorts of life forms, each species of fish has its own identification paint, similar to the uniforms of football players of one team. This allows other fish and individuals of the same species to instantly recognize it.
The coloring of the dogfish becomes brighter when it seeks to attract a female.
Dogfish - deadly dangerous predator
Dog fish belongs to the order of pufferfish or pufferfish, and there are more than ninety species of them. It differs from other fish unique ability swell up when frightened, swallowing a large volume of water or air. At the same time, she pricks with spikes, spewing out a nerve poison called tetrodotoxin, which is 1200 times more effective than potassium cyanide.
The dog-fish, due to the special structure of the teeth, was called the pufferfish. Puffer teeth are very strong, fused together, and look like four plates. With their help, she splits the shells of mollusks and crab shells, getting food. A rare case is known when live fish, not wanting to be eaten, bit off the cook's finger. Some species of fish are also able to bite, but the main danger is its meat. In Japan, this exotic fish is called fugu, skillfully cooked, it is at the top of the list of local cuisine delicacies. The price for one serving of such a dish reaches $ 750. When an amateur chef takes over its preparation, the tasting ends lethal outcome, because the skin and internal organs of this fish contain the strongest poison. First, the tip of the tongue goes numb, then the limbs, followed by convulsions and instant death. When gutting the fish, the dog emits a fetid, eerie odor.
The coloring of the Moorish idol fish is most striking when it hunts its prey.
The main body color is white. The edge of the upper jaw is black. The lower jaw is almost completely black. In the upper part of the muzzle there is a bright orange spot with a black border. There is a wide black stripe between the first dorsal fin and the ventral fin. Two thin, curved bluish stripes run from the first black stripe, from the beginning pelvic fins to the front of the dorsal fin, and from the abdomen to the base of the dorsal fin. The third, less noticeable, bluish stripe is located from the eyes towards the back. The second, gradually expanding, wide black stripe is located from the dorsal rays in the direction of the ventral ones. Behind the second wide black stripe is a thin vertical white line. A bright yellow-orange spot with a thin white border extends from the tail to the middle of the body, where it gradually merges with the main white color. The caudal fin is black with white trim.
Day and night coloring
At night, the fusilier fish sleeps on seabed, taking on a dark coloration that matches the color sea depths and bottom. Waking up, it brightens and becomes completely light as it approaches the surface. By changing color, it becomes less noticeable.
awake fish
Waking up fish
sleeping fish
Warning coloration
Seeing from afar brightly colored harlequin toothfish”, other fish immediately understand that this hunting area is already occupied.
Warning coloration
The bright coloring warns the predator: beware, this creature tastes bad or is poisonous! Pointy-nosed pufferfish extremely poisonous, and other fish do not touch it. In Japan, this fish is considered edible, but when cutting it, an experienced connoisseur must be present to remove the poison and make the meat harmless. And yet this fish, called fugu and considered a delicacy, claims the lives of many people every year. So, in 1963, viper fish were poisoned by meat and 82 people died.
The puffer fish is not at all scary in appearance: it is only the size of a palm, swims with its tail forward, very slowly. Instead of scales - thin elastic skin, capable of inflating in case of danger to a size three times larger than the original - a kind of goggle-eyed, outwardly harmless ball.
However, her liver, skin, intestines, caviar, milk, and even her eyes contain tetrodoxin, a strong nerve poison, 1 mg of which is a lethal dose for humans. An effective antidote for it does not yet exist, although the poison itself, in microscopic doses, is used to prevent age-related diseases, as well as to treat diseases of the prostate gland.
Multicolor Mystery
Most starfish move very slowly and live on clean bottoms, not hiding from enemies. Faded, muted tones would help them to become invisible, and it is very strange that the stars have such a bright color.
Depending on the habitat, the body color of the fish acquires characteristic features that make it possible to distinguish pelagic, bottom, thicket and schooling coloration.
Pelagic fish
The term "pelagic fish" comes from the place in which they live. This area is the area of the sea or ocean, which does not border the bottom surface. Pelageal - what is it? From the Greek "pelagial" is interpreted as "open sea", which serves as a habitat for nekton, plankton and pleuston. Conventionally, the pelagic zone is divided into several layers: epipelagic - located at a depth of up to 200 meters; mesopelagial - at a depth of up to 1000 meters; bathypelagial - up to 4000 meters; over 4000 meters - abyspelagial.
Popular types
The main commercial catch of fish is pelagic. It accounts for 65-75% of the total catch. Due to the large natural supply and availability, pelagic fish are the most inexpensive type of seafood. However, this has no effect on palatability and utility. The leading position of the commercial catch is occupied by pelagic fish of the Black Sea, the North Sea, the Sea of Marmara, the Baltic Sea, as well as the seas of the North Atlantic and the Pacific basin. These include smelt (capelin), anchovy, herring, herring, horse mackerel, cod (blue whiting), mackerel.
bottom fish- most life cycle carried out at the bottom or in close proximity to the bottom. They are found both in coastal regions of the continental shelf and in the open ocean along the continental slope.
Bottom fish can be divided into two main types: purely bottom and benthopelagic, which rise above the bottom and swim in the water column. In addition to the flattened shape of the body, an adaptive feature of the structure of many bottom-dwelling fish is the lower mouth, which allows them to feed from the ground. Sand sucked in with food is usually ejected through gill slits.
overgrown coloring
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 the tropical zone, can be very brightly colored.
Examples of fish with overgrown coloration are: common perch and pike - from freshwater forms; sea scorpion ruff, many wrasses and coral fish are from marine.
Vegetation, as an element of the landscape, is also important for adult fish. Many fish are specially adapted to life in thickets. They have a corresponding protective coloration. or a special form of the body, reminiscent of ts zardeli, among which the fish lives. So, the long outgrowths of the fins of the rag-picker seahorse, in combination with the corresponding color, make it completely invisible among the underwater thickets.
flock coloring
A number of features in the structure are also associated with a schooling lifestyle, in particular the color of fish. Schooling coloration helps fish to orient themselves to each other. In those fish in which a schooling lifestyle is characteristic only of juveniles, accordingly, schooling coloration can also appear.
A moving flock is different in shape from a stationary one, which is associated with the provision of favorable hydrodynamic conditions for movement and orientation. The shape of a moving and stationary school differs in different species of fish, and np may be different in the same species. A moving fish forms a certain force field around its body. Therefore, when moving in a flock, fish adjust to each other in a certain way. Flocks are grouped from fish usually of close sizes and a similar biological state. Fish in a flock, unlike many mammals and birds, apparently do not have a permanent leader, and they alternately focus either on one or the other of their member, or, more often, on several fish at once. Fish navigate in a flock with the help, first of all, of the organs of vision and the lateral line.
Mimicry
One of the adaptations is color change. Flat fish are masters of this miracle: they can change color and its pattern in accordance with the pattern and color of the seabed.
Presentation Hosting
Pisces are extremely various colors with a very strange design. A special 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 mostly retain the pattern characteristic of this species. Take at least a pike: its color changes from dark green to bright yellow color. The perch usually has bright red fins, a greenish color from the sides and a dark back, but there are whitish perches (in rivers) and, conversely, dark ones (in ilmens). All such observations suggest that the color of fish depends on their systematic position from the habitat environmental factors, nutritional conditions.
The coloration of fish is due to special cells found in skin-containing pigment grains. Such cells are called chromatophores.
Distinguish: melanophores (contain black pigment grains), erythrophores (red), xanthophores (yellow) and guanophores, iridocytes (silver color).
Although the latter are considered chromatophores and do not have pigment grains, they contain a 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 the chromatophores is very diverse, however, the most common are stellate and discoid.
In terms of chemical resistance, the black pigment (melanin) is the most resistant. It is not soluble in acids, 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 of the boundary layer (cutis). Guanophores (or leukophores, 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 plasma of the cell, like pigment grains, and its concentration can change due to intracellular plasma currents (thickening, thinning). Guanine crystals are hexagonal in shape and, depending on their location in the cell, the color changes from silvery-whitish to bluish-violet.
Guanophores in many cases are found together with melanophores and erythrophores. They play a very important biological role in the life of fish, because located on the abdominal surface and on the sides, they make the fish less noticeable from below and from the sides; the protective role of coloring is especially pronounced here.
The function of pigment staves is mainly to expand, i.e. occupying more space (expansion) and reducing i.e. occupying the smallest space (contract). When the plasma contracts, decreasing in volume, the pigment grains in the plasma are concentrated. Thanks to this most of the surface of the cell is released 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 body of the fish 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 (the physiological state of the cell, organism), and some factors. external environment(temperature, content of oxygen and carbon dioxide inlet). Melanophores have innervation. Canthophores and erythrophores lack innervation: Therefore, the nervous system can only have a direct effect on melanophores.
It has been established that the pigment cells of bony fish retain a constant shape. Koltsov believes that the plasma of a pigment cell has two layers: ectoplasm (surface layer) and kinoplasm (inner layer) containing pigment grains. The ectoplasm is fixed by radial fibrils, while the kinoplasm is highly mobile. Ectoplasm determines the external form of the chromatophore (the form of ordered movement), regulates metabolism, and changes its function under the influence of the nervous system. Ectoplasm and kinoplasm, having different physical and chemical properties, mutual wettability when their properties change under the influence of the external environment. During expansion (expansion), the kinoplasm wets the ectoplasm well and, due to this, spreads through the cracks covered with ectoplasm. The pigment grains are located in the kinoplasm, are well moistened with it, and follow the flow of the kinoplasm. At concentration, the reverse picture is observed. There is a separation of two colloidal layers of protoplasm. The kinoplasm does not wet the ectoplasm and due to this the kinoplasm
occupies the smallest volume. This process is based on a change in surface tension at the boundary of two layers of protoplasm. Ectoplasm by its nature is a protein solution, and kinoplasm is a lecithin-type lipoid. Kinoplasm is emulsified (very finely divided) in ectoplasm.
In addition to nervous regulation, chromatophores also have hormonal regulation. It must be assumed that under different conditions one or another regulation is carried out. A striking adaptation of body color to the color of the environment is observed in sea needles, gobies, flounders. 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, by transforming this perception, the nervous system controls the function of the pigment cells.
In other cases, hormonal regulation clearly appears (coloration during the breeding season). In the blood of fish there are hormones of the adrenal gland adrenaline and the posterior pituitary gland - pituitrin. Adrenaline causes concentration, pituitrin is an antagonist of adrenaline and causes expansion (diffusion).
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.) matter. The time required to change the color of the fish is different 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 the environment. Such copying is carried out only if the fish can see the color and pattern of the ground. This is evidenced by the following example. If the flounder lies on a black board, but does not see it, then it does not have the color of a black board, but of the white soil visible to it. On the contrary, if a flounder lies on white ground, but sees a black board, then its body acquires the color of a black board. These experiments convincingly show that fish easily adapt, changing their color to an unusual ground for them.
Lighting affects the color of the fish. "Like in dark places where there is low light, fish lose their color. Bright fish that have lived for some time in the dark become pale in color. Blinded fish become dark in color. In dark places, the fish becomes dark in color, in light light. Frisch managed to establish that the darkening and the lightening of the body of the fish depends not only on the illumination of the ground, but also on the angle of view at which the fish can see the ground.So, if the eyes of a trout are tied or removed, the fish becomes black.If you cover up only the lower half of the eye, the fish becomes dark, and if you glue only the upper half of the eye, then the fish retains its color.
Light has the strongest and most varied influence on the color of fish. Light
affects melanophores both through the eyes and nervous system, and directly. So Frisch, illuminating certain areas of the skin of the fish, received a local change in color: a darkening of the illuminated area (expansion of melanophores) was observed, which disappeared 1-2 minutes after the light was turned off. In connection with prolonged illumination in fish, the color of the back and abdomen changes. Usually the back of fish living on shallow depths and in clear waters it has a dark tone, and the belly is light. In fish living at great depths and muddy waters no such color difference is observed. It is believed that the difference in the coloration of the back and abdomen has an adaptive value: the dark back of the fish is less visible from above against a dark background, and the light abdomen from below. In this case, the different coloration of the abdomen and back is due to the uneven arrangement 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.
With local heating of the skin, the expansion of melanophores occurs, leading to darkening, while cooling - to lightening. A decrease in the concentration of oxygen and an increase in the concentration of carbonic acid also change the color of the fish. You probably observed that in fish after death, the part of the body that was in the water has a lighter color (melanophore concentration), and the part that protrudes from the water and comes into contact with the air is dark (melanophore expansion). The fish are in a normal state, usually the color is bright, multi-colored. With a sharp decrease in oxygen or in a state of suffocation, it becomes paler, dark tones almost completely disappear. The fading of the color of the integument of the fish network is the result of the concentration of chromatophores and , primarily melanophores. As a result of a lack of oxygen, the skin surface of the fish is not supplied with oxygen as a result of circulatory arrest or a poor supply of oxygen to the body (the beginning of suffocation), it always acquires pale tones. An increase in carbon dioxide in the 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 action of hormones on the color of fish is revealed, first of all, during mating season(breeding period). Especially interesting coloring skin and fins observed in males. The function of chromatophores is under the control of hormonal agents and the feather system. Example with fighting fish. In this case, mature males, under the influence of hormones, acquire the corresponding coloration, the brightness and brilliance of which is enhanced by the sight of a female. The eyes of the male see the female, this perception is transmitted through the nervous system to the chromatophores and causes them to expand. The male skin chromatophores function in this case under the control of hormones and the nervous system.
Experimental work on the minnow showed that the injection of adrenaline causes a lightening of the integument of the fish (melanophore contraction). A microscopic examination of the skin of an adrenalized minnow showed that melanophores are in a state of contraction, and lipophores are in expansion.
Questions for self-examination:
1. The structure and functional significance of fish skin.
2. The mechanism of mucus formation, its composition and significance.
3. Structure and functions of scales.
4. Physiological role of skin and scale regeneration.
5. The role of pigmentation and coloration in the life of fish.
Section 2: Materials of laboratory works.
Why do fish need bright colors? What is the origin of the varied pigmentation of fish? What is mimicry? Who sees the bright colors of fish at a depth where eternal darkness reigns? About how the color of fish correlates with their behavioral reactions and what social functions it has - biologists Alexander Mikulin and Gerard Chernyaev.
Topic overview
Coloration is of great ecological importance for fish. There are protective and warning colors. The protective coloration is intended to camouflage the fish against the background of the environment. Warning, or sematic, coloration usually consists of conspicuous large, contrasting spots or bands that have clear boundaries. It is intended, for example, in poisonous and poisonous fish, to prevent a predator from attacking them, and in this case it is called a deterrent. Identification coloration is used to warn territorial fish of rivals, or to attract females to males, warning them that males are ready to spawn. The last type of warning coloration is commonly referred to as the mating dress of fish. Often the identification coloration unmasks the fish. It is for this reason that in many fish guarding the territory or their offspring, the identification coloration in the form of a bright red spot is located on the belly, shown to the opponent if necessary, and does not interfere with the masking of the fish when it is located belly to the bottom.
There is also a pseudosematic coloration that mimics the warning coloration of another species. It is also called mimicry. It allows harmless species of fish to avoid the attack of a predator that takes them for a dangerous species.
There are other color classifications. For example, types of fish coloration are distinguished, reflecting the characteristics of the ecological confinement of this species. Pelagic coloration is characteristic of near-surface inhabitants of fresh and marine waters. It is characterized by a black, blue or green back and silvery sides and belly. The dark back makes the fish less visible against the bottom. River fish have black and dark brown backs, so they are less noticeable against the background of a dark bottom. In lake fish, the back is colored in bluish and greenish tones, since this color of their back is less noticeable against the background of greenish water. The blue and green back is characteristic of most marine pelagic fish, which hides them against the background of the blue depths of the sea. The silvery sides and light belly of the fish are poorly visible from below against the background of a mirror surface. The presence of a keel on the belly of pelagic fish minimizes the shadow that forms from the ventral side and unmasks the fish. When looking at the fish from the side, the light falling on the dark back, and the shadow of the lower part of the fish, hidden by the sheen of the scales, give the fish a gray, inconspicuous appearance.
The bottom coloration is characterized by a dark back and sides, sometimes with darker stains, and a light belly. In bottom fish living above the pebbly soil of rivers with clear water, usually on the sides of the body there are light, black and other colored spots, sometimes slightly elongated in the dorsal-abdominal direction, sometimes located in the form of a longitudinal strip (the so-called channel coloration). This coloration makes the fish inconspicuous against the background of pebble ground in a transparent flowing water. Bottom fish of stagnant freshwater reservoirs do not have bright dark spots on the sides of the body or they have blurred outlines.
The overgrown coloration of fish is characterized by a brownish, greenish or yellowish back and usually transverse or longitudinal stripes and stains on the sides. This coloration is characteristic of fish that live among underwater vegetation and coral reefs. Transverse stripes are characteristic of ambush predators hunting from an ambush of coastal thickets (pike, perch), or fish swimming slowly among them (barbs). Fish living near the surface, among the algae lying on the surface, are characterized by longitudinal stripes (zebrafish). The stripes not only mask the fish among the algae, but also dissect the appearance of the fish. Dissecting coloration, often very bright against a background unusual for fish, is characteristic of coral fish where they are invisible against the backdrop of bright corals.
Schooling fish are characterized by schooling coloration. This coloration facilitates the orientation of individuals in the flock to each other. It usually appears on the background of other forms of coloration and is expressed either in the form of one or more spots on the sides of the body or on dorsal fin, or as a dark stripe along the body or at the base of the caudal peduncle.
Many peaceful fish have a "deceptive eye" in the back of the body, which disorients the predator in the direction of the prey's throw.
The whole variety of fish colors is due to special cells - chromatophores, which occur in the skin of fish and contain pigments. The following chromatophores are distinguished: melanophores containing black pigment grains (melanin); red erythrophores and yellow xanthophores, called lipophores, since the pigments (carotenoids) in them are dissolved in lipids; guanophores or iridocytes containing guanine crystals in their structure, which give the fish a metallic sheen and silvery scales. Melanophores and erythrophores are stellate, xanthophores are rounded.
Chemically, the pigments of different pigment cells differ significantly. Melanins are polymers with a relatively high molecular weight black, brown, red or yellow.
Melanins are very stable compounds. They are insoluble in any of the polar or non-polar solvents, nor in acids. However, melanins can discolor in bright sunlight, prolonged exposure to air, or, especially effectively, prolonged oxidation with hydrogen peroxide.
Melanophores are capable of synthesizing melanins. The formation of melanin occurs in several stages due to the sequential oxidation of tyrosine to dihydroxyphenylalanine (DOPA) and then until the polymerization of the melanin macromolecule occurs. Melanins can also be synthesized from tryptophan and even from adrenaline.
In xanthophores and erythrophores, the predominant pigments are carotenoids dissolved in fats. In addition to them, these cells can contain pterins, either without carotenoids or in combination with them. The pterins in these cells are localized in specialized small organelles called pterinosomes, which are located throughout the cytoplasm. Even in species that are colored mainly by carotenoids, pterins are first synthesized and become visible in the developing xanthophores and erythrophores, while carotenoids, which must be obtained from food, are detected only later.
Pterins provide yellow, orange, or red coloration in a number of fish groups, as well as in amphibians and reptiles. Pterins are amphoteric molecules with weak acidic and basic properties. They are poorly soluble in water. Synthesis of pterins occurs through purine (guanine) intermediates.
Guanophores (iridophores) are very diverse in shape and size. Guanophores are composed of guanine crystals. Guanine is a purine base. Hexagonal crystals of guanine are located in the plasma of guanophores and, due to plasma currents, can be concentrated or distributed throughout the cell. This circumstance, taking into account the angle of incidence of light, leads to a change in the color of the integument of fish from silver-white to bluish-violet and blue-green or even yellow-red. So, a brilliant blue-green stripe of a neon fish under the influence of electric current acquires a red luster, like erythrosonus. Guanophores, located in the skin below the rest of the pigment cells, in combination with xanthophores and erythrophores give green, and with these cells and melanophores - blue.
Another method of acquiring the bluish-green color of their integuments by fish has been discovered. It has been noted that not all oocytes are spawned by female lumpfish during spawning. Some of them remain in the gonads and acquire a bluish-green color in the process of resorption. In the post-spawning period, the blood plasma of lumpfish females acquires a bright green color. A similar blue-green pigment was found in the fins and skin of females, which, apparently, has an adaptive value during their post-spawning fattening in the coastal zone of the sea among algae.
According to some researchers, only melanophores are suitable for nerve endings, and melanophores have dual innervation: sympathetic and parasympathetic, while xanthophores, erythrophores and guanophores do not have innervation. The experimental data of other authors point to the nervous regulation of erythrophores as well. All types of pigment cells are subject to humoral regulation.
Changes in the color of fish occur in two ways: due to the accumulation, synthesis or destruction of the pigment in the cell and due to a change in the physiological state of the chromatophore itself without changing the pigment content in it. An example of the first method of color change is its enhancement during the pre-spawning period in many fish due to the accumulation of carotenoid pigments in xanthophores and erythrophores when they enter these cells from other organs and tissues. Another example: the dwelling of fish on a light background causes an increase in the formation of guanine in guanophores and at the same time the decay of melanin in melanophores and, conversely, the formation of melanin occurring on a dark background is accompanied by the disappearance of guanine.
With a physiological change in the state of the melanophore under the action of a nerve impulse, the pigment grains located in the moving part of the plasma - in the kinoplasm, together with it are collected in the central part of the cell. This process is called contraction (aggregation) of the melanophore. Due to contraction, the vast majority of the pigment cell is freed from pigment grains, resulting in a decrease in color brightness. At the same time, the form of the melanophore, supported by the cell surface membrane and skeletal fibrils, remains unchanged. The process of distribution of pigment grains throughout the cell is called expansion.
Melanophores located in the epidermis of lungfish and you and me are not capable of changing color due to the movement of pigment grains in them. In humans, darkening of the skin in the sun occurs due to the synthesis of pigment in melanophores, and enlightenment due to desquamation of the epidermis along with pigment cells.
Under the influence of hormonal regulation, the color of xanthophores, erythrophores and guanophores changes due to a change in the shape of the cell itself, and in xanthophores and erythrophores, and due to a change in the concentration of pigments in the cell itself.
The processes of contraction and expansion of pigment granules of melanophores are associated with changes in the processes of wettability of the kinoplasm and ectoplasm of the cell, leading to a change in the surface tension at the boundary of these two plasma layers. This is a purely physical process and can be carried out artificially even in dead fish.
Under hormonal regulation, melatonin and adrenaline cause contraction of melanophores, in turn, hormones of the posterior pituitary gland - expansion: pituitrin - melanophores, and prolactin causes expansion of xanthophores and erythrophores. Guanophores are also subject to hormonal influences. Thus, adrenaline increases the dispersion of platelets in guanophores, while an increase in the intracellular level of cAMP enhances platelet aggregation. Melanophores regulate the movement of the pigment by changing the intracellular content of cAMP and Ca ++, while in erythrophores, regulation is carried out only on the basis of calcium. A sharp increase in the level of extracellular calcium or its microinjection into the cell is accompanied by the aggregation of pigment granules in erythrophores, but not in melanophores.
The above data show that both intracellular and extracellular calcium play an important role in the regulation of expansion and contraction of both melanophores and erythrophores.
The coloration of fish in their evolution could not have arisen specifically for behavioral responses and must have some prior physiological function. In other words, the set of skin pigments, the structure of pigment cells and their location in the skin of fish are apparently not accidental and should reflect the evolutionary path of changes in the functions of these structures, during which modern organization pigment complex of the skin of living fish.
Presumably, initially the pigment system participated in the physiological processes of the body as part of the excretory system of the skin. Subsequently, the pigment complex of fish skin began to participate in the regulation of photochemical processes occurring in the corium, and at the later stages of evolutionary development, it began to perform the function of the actual coloration of fish in behavioral reactions.
For primitive organisms, the excretory system of the skin plays an important role in their life. Naturally, one of the tasks of reducing the harmful effects of metabolic end products is to reduce their solubility in water by polymerization. This, on the one hand, makes it possible to neutralize their toxic effect and simultaneously accumulate metabolites in specialized cells without them. significant costs with further removal of these polymer structures from the body. On the other hand, the polymerization process itself is often associated with elongation of structures that absorb light, which can lead to the appearance of colored compounds.
Apparently, purines, in the form of guanine crystals, and pterins ended up in the skin as products of nitrogen metabolism and were removed or accumulated, for example, in the ancient inhabitants of the swamps during periods of drought, when they fell into hibernation. It is interesting to note that purines and especially pterins are widely represented in the integument of the body not only of fish, but also of amphibians and reptiles, as well as arthropods, in particular insects, which may be due to the difficulty of their removal due to the emergence of these groups of animals on land. .
It is more difficult to explain the accumulation of melanin and carotenoids in the skin of fish. As mentioned above, melanin biosynthesis is carried out due to the polymerization of indole molecules, which are products of the enzymatic oxidation of tyrosine. Indole is toxic to the body. Melanin turns out to be an ideal option for the preservation of harmful indole derivatives.
Carotenoid pigments, in contrast to those discussed above, are not end products of metabolism and are highly reactive. They are of food origin and, therefore, to clarify their role, it is more convenient to consider their participation in metabolism in closed system, for example, in fish roe.
Over the past century, more than two dozen opinions have been expressed about the functional significance of carotenoids in the body of animals, including fish and their caviar. Particularly heated debate was about the role of carotenoids in respiration and other redox processes. Thus, it was assumed that carotenoids are capable of transmembranely transporting oxygen, or storing it along the central double bond of the pigment. In the seventies of the last century, Viktor Vladimirovich Petrunyaka suggested the possible participation of carotenoids in calcium metabolism. He discovered the concentration of carotenoids in certain areas of the mitochondria, called calcospherules. An interaction of carotenoids with calcium during the embryonic development of fish, due to which a change in the color of these pigments occurs, has been found.
It has been established that the main functions of carotenoids in fish roe are: their antioxidant role in relation to lipids, as well as participation in the regulation of calcium metabolism. They are not directly involved in the processes of respiration, but purely physically contribute to the dissolution, and, consequently, the storage of oxygen in fatty inclusions.
The views on the functions of carotenoids have fundamentally changed in connection with structural organization their molecules. Carotenoids consist of ionic rings, including oxygen-containing groups - xanthophylls, or without them - carotenes and a carbon chain, including a system of double conjugated bonds. Previously, changes in the groupings in the ionone rings of their molecules, that is, the transformation of some carotenoids into others, were of great importance in the functions of carotenoids. We have shown that the qualitative composition in the work of carotenoids of great importance does not, and the functionality of carotenoids is associated with the presence of a conjugation chain. It determines the spectral properties of these pigments, as well as the spatial structure of their molecules. This structure quenches the energy of radicals in the processes of lipid peroxidation, performing the function of antioxidants. It provides or interferes with the transmembrane transport of calcium.
There are other pigments in fish caviar. Thus, a pigment close in light absorption spectrum to bile pigments and its protein complex in scorpion fish determine the diversity of the color of eggs of these fish, ensuring the detection of native clutch. A unique hemoprotein in the yolk of whitefish eggs contributes to its survival during development in the pagon state, that is, when it freezes into ice. It contributes to the idle burning of part of the yolk. It was found that its content in caviar is higher in those species of whitefish, the development of which occurs in more severe conditions. temperature conditions winters.
Carotenoids and their derivatives - retinoids, such as vitamin A, are able to accumulate or transmembrane transfer salts of divalent metals. This property, apparently, is very important for marine invertebrates, which remove calcium from the body, which is later used in the construction of the external skeleton. Perhaps this is the reason for the presence of an external rather than an internal skeleton in the vast majority of invertebrates. It is well known that external calcium-containing structures are widely represented in sponges, hydroids, corals, and worms. They contain significant concentrations of carotenoids. In mollusks, the main mass of carotenoids is concentrated in motile mantle cells - amoebocytes, which transport and secrete CaCO 3 into the shell. In crustaceans and echinoderms, carotenoids in combination with calcium and protein are part of their shell.
It remains unclear how these pigments are delivered to the skin. It is possible that phagocytes were the original cells delivering pigments to the skin. Macrophages that phagocytize melanin have been found in fish. The similarity of melanophores with phagocytes is indicated by the presence of processes in their cells and the amoeboid movement of both phagocytes and melanophore precursors to their permanent locations in the skin. When the epidermis is destroyed, macrophages also appear in it, consuming melanin, lipofuscin and guanine.
The place of formation of chromatophores in all classes of vertebrates is the accumulation of cells of the so-called neural crest, which arises above the neural tube at the site of separation of the neural tube from the ectoderm during neurulation. This detachment is carried out by phagocytes. Chromatophores in the form of unpigmented chromatoblasts at the embryonic stages of fish development are able to move to genetically predetermined areas of the body. More mature chromatophores are not capable of amoeboid movements and do not change their shape. Further, a pigment corresponding to this chromatophore is formed in them. AT embryonic development bony fish chromatophores different types appear in a certain sequence. Dermal melanophores differentiate first, followed by xanthophores and guanophores. In the process of ontogenesis, erythrophores originate from xanthophores. Thus, the early processes of phagocytosis in embryogenesis coincide in time and space with the appearance of unpigmented chromatoblasts, precursors of melanophores.
Thus, a comparative analysis of the structure and functions of melanophores and melanomacrophages gives reason to believe that at the early stages of animal phylogenesis, the pigment system, apparently, was part of the excretory system of the skin.
Having appeared in the surface layers of the body, pigment cells began to perform a different function, not related to excretory processes. In the dermal layer of the skin of bony fish, chromatophores are localized in a special way. Xanthophores and erythrophores are usually located in the middle layer of the dermis. Below them lie guanophores. Melanophores are found in the lower dermis below the guanophores and in the upper dermis just below the epidermis. This arrangement of pigment cells is not accidental and, possibly, due to the fact that photoinduced processes of synthesis of a number of substances important for metabolic processes, in particular, vitamins of group D, are concentrated in the skin. To perform this function, melanophores regulate the intensity of light penetration into the skin, and guanophores perform the function of a reflector, passing light twice through the dermis when it is lacking. It is interesting to note that direct exposure to light on skin areas leads to a change in the response of melanophores.
There are two types of melanophores, differing in appearance, localization in the skin, reactions to nervous and humoral influences.
In higher vertebrates, including mammals and birds, mainly epidermal melanophores, more commonly referred to as melanocytes, are found. In amphibians and reptiles, they are thin elongated cells that play a minor role in the rapid color change. There are epidermal melanophores in primitive fish, in particular lungfish. They do not have innervation, do not contain microtubules, and are not capable of contraction and expansion. To a greater extent, the change in the color of these cells is associated with their ability to synthesize their own melanin pigment, especially when exposed to light, and the weakening of the color occurs in the process of desquamation of the epidermis. Epidermal melanophores are characteristic of organisms living either in drying up water bodies and falling into anabiosis (lungfish), or living out of water (terrestrial vertebrates).
Almost all poikilothermic animals, including fish, have dendro-shaped dermal melanophores that quickly respond to nervous and humoral influences. Considering that melanin is not reactive, it cannot perform any other physiological functions, except for screening or dosed transmission of light into the skin. It is interesting to note that the process of tyrosine oxidation from a certain moment goes in two directions: towards the formation of melanin and towards the formation of adrenaline. In evolutionary terms, in ancient chordates, such oxidation of tyrosine could occur only in the skin, where oxygen was available. At the same time, adrenaline itself modern fish acts through the nervous system on melanophores, and in the past, possibly produced in the skin, directly led to their contraction. Given that the excretory function was originally performed by the skin, and, later, the kidneys, which are intensively supplied with blood oxygen, specialized in performing this function, chromaffin cells in modern fish that produce adrenaline are located in the adrenal glands.
Let us consider the formation of the pigment system in the skin during the phylogenetic development of primitive chordates, pisciformes, and fish.
The lancelet has no pigment cells in the skin. However, the lancelet has an unpaired photosensitive pigment spot on the anterior wall of the neural tube. Also, along the entire neural tube, along the edges of the neurocoel, there are light-sensitive formations - Hesse's eyes. Each of them is a combination of two cells: photosensitive and pigment.
In tunicates, the body is dressed in a single-layer cellular epidermis, which highlights on its surface a special thick gelatinous membrane - a tunic. Vessels pass through the thickness of the tunic, through which blood circulates. There are no specialized pigment cells in the skin. There are no tunicates and specialized excretory organs. However, they have special cells - nephrocytes, in which metabolic products accumulate, giving them and the body a reddish-brown color.
Primitive cyclostomes have two layers of melanophores in their skin. In the upper layer of the skin - the corium, under the epidermis there are rare cells, and in the lower part of the corium there is a powerful layer of cells containing melanin or guanine, which shields the light from entering the underlying organs and tissues. As mentioned above, lungfish have non-innervated stellate epidermal and dermal melanophores. In phylogenetically more advanced fish, melanophores, capable of changing their light transmission due to nervous and humoral regulation, are located in the upper layers under the epidermis, and guanophores - in the lower layers of the dermis. In bony ganoids and teleosts, xanthophores and erythrophores appear in the dermis between the layers of melanophores and guanophores.
In the process of phylogenetic development of lower vertebrates, in parallel with the complication of the pigment system of the skin, the organs of vision improved. It was the photosensitivity of nerve cells in combination with the regulation of light transmission by melanophores that formed the basis for the emergence of visual organs in vertebrates.
Thus, the neurons of many animals respond to illumination by a change in electrical activity, as well as an increase in the rate of neurotransmitter release from nerve endings. Nonspecific photosensitivity of nervous tissue containing carotenoids was found.
All parts of the brain are photosensitive, but the middle part of the brain, located between the eyes, and the pineal gland are the most photosensitive. In the cells of the pineal gland there is an enzyme whose function is the conversion of serotonin to melatonin. The latter causes contraction of skin melanophores and retardation of the growth of gonads of producers. When the pineal gland is illuminated, the concentration of melatonin in it decreases.
It is known that sighted fish darken on a dark background, and brighten on a light background. However, bright light causes darkening of the fish due to a decrease in the production of melatonin by the pineal gland, and low or no light causes brightening. Similarly, fish react to light after removing their eyes, that is, they brighten in the dark and darken in the light. It was noted that in a blind cave fish, residual melanophores of the scalp and middle part of the body react to light. In many fish, when they mature, due to the hormones of the pineal gland, the color of the skin intensifies.
A light-induced color change in reflection by guanophores was found in fundulus, red neon, and blue neon. This indicates that the change in the color of the luster, which determines day and night coloration, depends not only on the visual perception of light by the fish, but also on the direct effect of light on the skin.
In embryos, larvae and fry of fish developing in the upper, well-lit layers of water, melanophores, on the dorsal side, cover the central nervous system from exposure to light and it seems that all five parts of the brain are visible. Those developing at the bottom have no such adaptation. Exposure to light on eggs and larvae of the Sevan whitefish causes an increased synthesis of melanin in the skin of embryos during the embryonic development of this species.
The melanophore-guanophore system of light regulation in fish skin, however, has a drawback. To perform photochemical processes, a light sensor is needed, which would determine how much light actually passed into the skin, and would transmit this information to melanophores, which should either enhance or weaken the light flux. Consequently, the structures of such a sensor must, on the one hand, absorb light, i.e., contain pigments, and, on the other hand, report information about the magnitude of the flux of light falling on them. To do this, they must be highly reactive, be fat-soluble, and also change the structure of membranes under the action of light and change its permeability to various substances. Such pigment sensors should be located in the skin below the melanophores, but above the guanophores. It is in this place that erythrophores and xanthophores containing carotenoids are located.
As is known, carotenoids are involved in light perception in primitive organisms. Carotenoids are present in the eyes of unicellular organisms capable of phototaxis, in the structures of fungi, the hyphae of which react to light, in the eyes of a number of invertebrates and fish.
Later, in more highly developed organisms, carotenoids in the organs of vision are replaced by vitamin A, which does not absorb light in the visible part of the spectrum, but, being part of rhodopsin, is also a pigment. The advantage of such a system is obvious, since colored rhodopsin, having absorbed light, decomposes into opsin and vitamin A, which, unlike carotenoids, do not absorb visible light.
The division of the lipophores themselves into erythrophores, which are capable of changing light transmission under the action of hormones, and xanthophores, which, in fact, apparently, are light detectors, allowed this system to regulate photosynthetic processes in the skin, not only when light is simultaneously exposed to the body from the outside, but also to correlate it is with the physiological state and the body's needs for these substances, hormonally regulating light transmission through both melanophores and erythrophores.
Thus, the coloration itself, apparently, was a transformed consequence of the performance by pigments of other physiological functions associated with the surface of the body and, picked up by evolutionary selection, acquired an independent function in mimicry and for signaling purposes.
emergence various types coloring initially had physiological causes. So, for the inhabitants of surface waters, influenced significant insolation, powerful melanin pigmentation is required on the dorsal part of the body in the form of melanophores of the upper dermis (to regulate the transmission of light into the skin) and in the lower layer of the dermis (to shield the body from excess light). On the sides and especially the belly, where the intensity of light penetration into the skin is less, it is necessary to reduce the concentration of melanophores in the skin with an increase in the number of guanophores. The appearance of such coloration in pelagic fish simultaneously contributed to a decrease in the visibility of these fish in the water column.
Juvenile fish react to the intensity of illumination to a greater extent than to a change in the background, that is, in complete darkness they brighten, and darken in the light. This indicates the protective role of melanophores against excessive exposure to light on the body. In this case, fish fry, due to their smaller size than adults, are more susceptible to the harmful effects of light. This is confirmed by the significantly greater death of fry less pigmented with melanophores when exposed to direct rays of sunlight. On the other hand, darker fry are eaten more intensively by predators. The impact of these two factors: light and predators leads to the occurrence of diurnal vertical migrations in most fish.
In juveniles of many species of fish that lead a schooling lifestyle at the very surface of the water, in order to protect the body from excessive exposure to light, a powerful layer of guanophores develops on the back under the melanophores, giving the back a bluish or greenish tint, and in the fry of some fish, such as mullets, the back is behind guanine literally glows with reflected light, protecting from excessive insolation, but also making fry visible to fish-eating birds.
In many tropical fish that live in small streams shaded by the forest canopy from sunlight, a layer of guanophores is enhanced in the skin under the melanophores, for the secondary transmission of light through the skin. In such fish, species are often found that additionally use guanine luster in the form of “luminous” stripes, like neons, or spots as a guide when creating flocks or in spawning behavior to detect individuals of the opposite sex of their species in the twilight.
Marine bottom fish, often flattened in the dorso-ventral direction and leading a sedentary lifestyle, must have, in order to regulate photochemical processes in the skin, rapid changes in individual groups of pigment cells on their surface in accordance with the local focusing of light on their skin surface, which occurs during the process. its refraction by the surface of the water during waves and ripples. This phenomenon could be picked up by selection and lead to the emergence of mimicry, expressed in a rapid change in the tone or pattern of the body to match the color of the bottom. It is interesting to note that sea bottom inhabitants or fish whose ancestors were bottom usually have a high ability to change their color. In fresh waters, the phenomenon of "sunbeams" at the bottom, as a rule, does not occur, and there are no fish with a rapid color change.
With depth, the light intensity decreases, which, in our opinion, leads to the need to increase light transmission through the integument, and, consequently, to a decrease in the number of melanophores with a simultaneous increase in the regulation of light penetration with the help of lipophores. It is with this, apparently, that it becomes red in many semi-deep-water fish. Red pigments at a depth where the red rays of sunlight do not reach appear black. At great depths, fish are either colorless or, in luminous fish, have a black color. In this they differ from cave fish, where in the absence of light there is no need at all for a light-regulating system in the skin, in connection with which melanophores and guanophores disappear in them, and last of all, in many, lipophores.
The development of protective and warning coloration in different systematic groups of fish, in our opinion, could proceed only on the basis of the level of organization of the pigment complex of the skin of a particular group of fish that had already arisen in the process of evolutionary development.
Thus, such a complex organization of the skin pigment system, which allows many fish to change color and adapt to different living conditions, had its own prehistory with a change in functions, such as participation in excretory processes, in skin photoprocesses, and, finally, in the actual color of the body of fish.
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The color of the fish is very diverse. AT Far Eastern waters 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, 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, 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 highly 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 sea fish, 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 color tropical butterflies and birds. Azure, yellowish green, velvety black and striped fish flicker and curl in crowds. You involuntarily take up 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 patronizing coloration: the white abdomen 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 red fish ( sea bass), pink (liparis) and dark brown (pinagore) flowers. 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 was once in large numbers lived 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 whitefish, 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: grey colour her back merges with the color of 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.