How fish see. Structure and physiological characteristics of fish

A person sees very poorly under water. The ability to refract light rays in water and the lens of the eye of terrestrial animals is almost the same, so the rays are concentrated at a focus far behind the retina. On the retina itself, an unclear, blurry image is obtained.

The lens of the fish's eye is spherical; it refracts rays better, but cannot change shape. And yet, to some extent, fish can adapt their vision to distance. They achieve this by bringing the lens closer to or moving away from the retina using special muscles.

In practice, fish in clear water can see no further than 10-12 meters, but clearly - only within one and a half meters.

The angle of view of fish is very wide. Without turning their body, they can see objects with each eye vertically in a zone of about 150° and horizontally up to 170°. This is explained by the location of the eyes on both sides of the head and the position of the lens, shifted towards the cornea itself.

The surface world must seem completely unusual to the fish. Without distortion, the fish sees only objects located directly above its head - at the zenith. For example, a cloud or a soaring seagull. But the sharper the angle of entry of the light beam into the water and the lower the surface object is located, the more distorted it appears to the fish. When the light beam falls at an angle of 5-10°, especially if the water surface is choppy, the fish stops seeing the object altogether.

The rays coming from the eye of the fish outside the cone of 97.6° are completely reflected from the water surface, and it appears mirror-like to the fish. It reflects the bottom, aquatic plants, and swimming fish.

On the other hand, the peculiarities of the refraction of rays allow the fish to see seemingly hidden objects. Let's imagine a body of water with a steep, steep bank. A person sitting on the shore will not see the fish - it is hidden by the coastal ledge, but the fish will see the person.

Objects half-submerged in water look fantastic. This is how, according to L. Ya. Perelman, a person who is chest-deep in water should appear to fish: “For them, walking through shallow water, we split into two, turning into two creatures: the upper one is legless, the lower one is headless with four legs! When We are moving away from the underwater observer, the upper half of our body is increasingly compressed in the lower part; at some distance almost the entire surface body disappears - only one freely floating head remains."

Even when going underwater, it is difficult for a person to check how fish see. With the naked eye he will not see anything clearly at all, but when looking through a glass mask or from the window of a submarine, he will see everything in a distorted form. Indeed, in these cases, there will also be air between the human eye and the water, which will certainly change the course of the light rays.

How fish see objects located outside the water was verified by underwater photography. Using special photographic equipment, photographs were obtained that fully confirmed the considerations expressed above. An idea of how the surface world appears to underwater observers can be formed by lowering a mirror under water. At a certain tilt, we will see the reflection of surface objects in it.

The structural features of the fish eye, as well as other organs, depend primarily on the living conditions and their lifestyle.

More sharp than others are the daytime predatory fish: trout, asp, pike. This is understandable: they detect prey mainly by sight. Fish that feed on plankton and bottom organisms can see well. Their vision is also of paramount importance for finding prey.

Our freshwater fish - bream, pike perch, catfish, burbot - hunt more often at night. They need to see well in the dark. And nature took care of it. Bream and pike perch have a light-sensitive substance in the retina of their eyes, and catfish and burbot even have special bundles of nerves that perceive the weakest light rays.

Anomalops and photoblepharon fish, living in the waters of the Malay Archipelago, use their own lighting in the dark. The flashlights are located near their eyes and shine forward, just like car headlights. The glow is caused by bacteria located in special cones. The lanterns can be switched on and off at the owners' request. Anomalops turns them off, turning the luminous side inward, and photoblepharon closes the lanterns, like a curtain, with a fold of skin.

The location of the eyes on the head also depends on the lifestyle. Many bottom fish - flounder, catfish, stargazer - have eyes located in the upper part of the head. This allows them to better see enemies and prey passing above them. Interestingly, in infancy, flounder eyes are located in the same way as most fish - on both sides of the head. At this time, flounders have a cylindrical body shape, live in the water column and feed on zooplankton. Later they switch to feeding on worms, mollusks, and sometimes fish. And then remarkable transformations occur with flounders: their left side begins to grow faster than their right, the left eye moves to the right side, the body becomes flat, and eventually both eyes end up on the right side. Having completed the transformation, flounders sink to the bottom and lie on their left side - it’s not for nothing that they are aptly nicknamed couch potatoes.

The eyes of flounders have another feature. They can turn in different directions independently of one another. This allows fish to simultaneously monitor the approach of prey or an enemy from the right and left.

Callichthys callichthys catfish

In hammerhead fish, the eyes are located at both ends of the hammer-shaped outgrowth. This is no coincidence. The hammerhead fish often hunts for stingrays, but some of them have spines on their tails, and if the hammerhead fish had a different eye position, they could easily get hurt.

Outside of water, the vast majority of fish are completely blind. But there are also exceptions. The mudskipper hunts for insects on land and sees well in the air, so that its eyes do not dry out in the air; they are hidden in its recesses.

Blennies also see well out of water. They spend a lot of time hunting on the coastal sand!

The eyes of the small viviparous fish Tetraphthalmus, which translated into Russian means four eyes, have a completely unusual arrangement. This fish lives in shallow lagoons of the tropical coast of South America. Her eyes are designed in such a way that they can see both in water and in air. They are divided into two parts by a horizontal partition. The septum divides the lens, the iris, and the cornea. It really turns out to be four eyes. The lower part of the lens is more convex and serves the fish for underwater vision; the upper one - flatter - gives her the opportunity to see well in the air. And since the four-eyed bird spends most of its time on the surface, with the upper part of its eye exposed, it can simultaneously monitor enemies and prey both in the air and under water.

The amount of light penetrating to different depths is not the same. It is light at the surface, but the deeper it is, the darker it is. At a depth of 200-300 meters, something is still visible, and below 500-600 meters the sun's rays do not penetrate at all. The darkness there is broken only by luminous organisms. Therefore, fish living at depths have eyes that are structured differently than fish living in the upper layers of water. What they are is described in the chapter “Fishes of the Deep”. The lighting in caves is also different. Therefore, among their inhabitants there are fish with a wide variety of eyes, some with very small ones, and some fish without eyes at all.

Anontychthys fish are especially interesting. They were discovered in cave ponds in Mexico in 1938. These fish emerge from eggs with eyes. At first, the fry stay in the upper layers of water and feed on zooplankton. Without eyes, it would be difficult for them to catch nimble ciliates and crustaceans. By the end of the second month of life, the fish switch to feeding on bottom invertebrates and descend into the depths. It is completely dark here, and not all fish need eyes to catch sedentary mollusks, so they are destroyed, overgrown with skin.

Pisces distinguish colors and even their shades.

Try putting several different colored cups into the aquarium, but only put food in one of them. Continue to provide food in the same colored cup each day. Soon the fish will begin to rush to the cup only of the color in which you usually gave them food; they will find the cup even if you put it in a different place.

Or another experiment: one side of the aquarium is covered with cardboard, leaving a narrow vertical gap in the middle. A white stick is placed at the opposite side of the aquarium, and rays are passed through the gap, coloring the stick in one color or another. Food is given to fish at a certain color. After some time, the fish begin to gather towards the stick as soon as it turns into a “food” color.

These experiments showed that fish perceive not only colors, but also their individual shades no worse than humans. Crucian carp, for example, are distinguished by lemon, yellow and orange.

The fact that fish have color vision is confirmed by their protective and mating coloration, because otherwise it would be simply useless. Blinded fish do not distinguish colors and always remain dark-colored.

Sports anglers know well that for successful fishing, the color of the lures used is not indifferent.

The ability to distinguish colors is not equally developed in different fish. Fish that live near the surface, where there is a lot of light, distinguish colors best. Worse are those who live in the depths, where only part of the light rays penetrate. There are also colorblind fish, such as stingrays.

Pisces do not respond equally to artificial light. It attracts some, repels others. For example, a fire built on the river bank attracts, according to old fishermen, roach, burbot, and catfish. In the Mediterranean Sea, fishermen have long caught sardines by luring them with the light of torches.

Research in recent years has shown that sprat, saury, mullet, syrti, and sardines always go to sources of underwater lighting. Fishermen used these features of fish. Now in the USSR, electric light is used in commercial fishing for sprat in the Caspian Sea, saury off the Kuril Islands, and sardines off the coast of Africa.

Sometimes overhead lighting sources are also used. In Congo on Lake Tanganyika, fishermen hang gas lamps from their catamarans. Ndakala fish rush towards the light. When enough fish are collected, they are caught with a net.

But lamprey, eel, and carp do not like light. This feature of fish is also used in fishing. On the Volga when catching lamprey, and in Denmark and Sweden - eel. They do it like this. A narrow dark corridor is left among the illuminated area. A net trap is set at the end of the corridor. The fish, avoiding the light, swim through a dark passage and fall into a trap. When catching carp with nets, bright light drives it out of snags.

Why fish come to the light has not been definitively established. According to one theory, in the sea, in places better illuminated by the sun, fish find more food. Plant plankton develops rapidly here, and many small crustaceans accumulate. And over a number of generations, fish have developed a positive reaction to light. The light became a food signal for them. This theory does not explain why fish that eat mollusks, and not just feed on plankton, rush to the light. It also does not explain why fish, having entered the illuminated area and not finding food, linger in it.

According to another theory, fish are drawn to light by “curiosity.” According to the teachings of I.P. Pavlov, animals are characterized by the “What is this?” reflex. Electric light is unusual under water and, noticing it, fish swim closer to get acquainted with the new phenomenon. Subsequently, near the light source, a wide variety of reflexes arise in different fish, depending on their lifestyle. If a defensive reflex occurs, the fish immediately swim away, but if a schooling or feeding reflex appears, the fish linger for a long time in the illuminated area.

Literature: Sabunaev Viktor Borisovich. Entertaining ichthyology, 1967

Read: Variety of fish: shape, size, color

Sense organs: fish vision

Read more: Sense organs of fish

Organs of vision. Fish vision.

The eyes of most fish are located on the sides of the head. Fish vision is monocular, i.e. each eye sees independently (field of view horizontally 160–170°, vertically about 150°). In many fish, the lens protrudes from the opening of the pupil, which increases the field of vision. In front, the monocular vision of each eye overlaps, and binocular vision is formed (total 15–30°). The main disadvantage of monocular vision is inaccurate distance estimation.

Many freshwater fish have a fixed pupil; some species can contract and dilate it (eels, flounders, stargazers, cartilaginous fish). The eyes of most fish do not have eyelids, some sharks have a nictitating membrane, and mullets and some herrings develop fatty eyelids.

In fish, the eye includes three membranes: 1) sclera (outer); 2) vascular (medium); 3) retina, or retina (inner).

The sclera protects the eye from mechanical damage; in the front part of the eye it forms a transparent, flattened cornea. The choroid supplies the eye with blood. In the area where the optic nerve enters the eye, there is a vascular gland characteristic of fish. In the front part of the eye, the choroid passes into the iris, which has an opening - the pupil, into which the lens protrudes.

The retina includes: 1) pigment layer (pigment cells); 2) photosensitive layer (photosensitive cells: rods and cones); 3) two layers of nerve cells.

Most fish have rods and cones in their retinas. Rods function in the dark and are insensitive to color; cones perceive color.

The lens in the upper part is supported by a ligament, and in the lower part it is attached with the help of a special muscle (Haller's bell) to the falciform process at the bottom of the eyeball, which is found in most bony fish. The lens of fish is spherical and does not change its shape. Accommodation (adjustment for sharpness) is carried out not by changing the curvature of the lens, but with the help of a muscle (Haller's bell), which tightens or removes the lens from the retina. The lens has the same density as water, as a result of which light passing through it is not refracted and a clear image is obtained on the retina.

Depending on the presence of light-sensitive cells (rods, cones), fish are divided into: 1) crepuscular (there is little melanin in the pigment layer, only rods are present in the retina); 2) daytime (there is a lot of melanin in the pigment layer, rods are few in the retina, cones are large).

Fish perceive light waves of 400–750 nm. Almost all fish (except crepuscular fish and most cartilaginous fish) have color vision and some of them can change body color. Fish have different visual acuity. They usually see objects at a distance of no more than 10–15 m. Cartilaginous fish are the most farsighted, as they are able to contract and dilate the pupil of the eye. With a decrease in illumination, in some species the size of the eyes increases, and they are able to capture weak light (deep-sea fish - sea bass, luminous anchovies), in others - the size of the eyes decreases (burbot, river eel). A number of deep-sea and cave fish do not have eyes.

In the air, fish almost cannot see with their eyes; some of them have special devices in their eyes for this purpose. In four-eyed fish, each eye is divided into two parts by a horizontal partition. At the top of the eye, the lens is simplified and the cornea is convex, allowing vision in air.

N.V. ILMAST. INTRODUCTION TO ICHTHYOLOGY. Petrozavodsk, 2005

The eye is a perfect optical device. It resembles a photographic camera. The lens of the eye is like a lens, and the retina is like a film on which the image is produced. In terrestrial animals, the lens is lenticular and can change its curvature, which makes it possible to adapt vision to distance. In fish, the lens of the eye is more convex, almost spherical, and cannot change shape. And yet, to some extent, fish adapt their vision to distance. They achieve this by moving the lens closer or further away from the retina using special muscles.

In clear water, fish can practically see no further than 10-12 m, but usually clearly distinguish objects within 1.5 m.

Pisces have a wide range of vision. Without turning their body, they can see objects with each eye vertically in a zone of about 150° and horizontally up to 170° (Fig. 87). This is explained by the location of the eyes on both sides of the head and the position of the lens, shifted towards the cornea itself.

The surface world must seem completely unusual to the fish. Without distortion, the fish sees only objects located directly above its head - at the zenith. For example, a cloud or a soaring seagull. But the smaller the angle of entry of the light beam into the water and the lower the surface object is located, the more distorted it appears to the fish.

Pisces are excellent at distinguishing colors and even their shades.

Or another experiment: one side of the aquarium is covered with cardboard, leaving a narrow vertical gap in the middle. A white stick is placed on the opposite side of it, and rays are passed through the gap, coloring the stick in one color or another. Food is given to fish at a certain color. After some time, the fish begin to gather towards the stick as soon as it turns “food” color. These experiments showed that fish perceive not only color, but also its individual shades no worse than humans. Crucian carp, for example, are distinguished by lemon, yellow and orange. The fact that fish have color vision is confirmed by their protective and mating coloration - otherwise it would be simply useless. Sports fishermen are well aware that the color of the lures used is important for successful fishing.

The ability to distinguish colors varies among different fish. The colors are best distinguished by fish that live in the upper layers of water, where there is a lot of light. Worse are those who live at a depth where only part of the light rays penetrate.

Fish react differently to artificial light. It attracts some, repels others.

Why fish come to the light has not been definitively established. According to one theory, in the sea, in places better illuminated by the sun, fish find more food. Plant plankton develops rapidly here, and many small crustaceans accumulate. And the fish developed a positive reaction to light, which became a “food” signal for them. This theory does not explain why fish that eat shellfish rush to the light. It also does not explain why fish, having found themselves in an illuminated area and not finding food, linger in it and do not swim away immediately.

According to another theory, fish are drawn to light by “curiosity.” According to the teachings of I.P. Pavlov, animals are characterized by a reflex - “What is this?” The electric light is unusual underwater, and when the fish notice it, they swim closer. Subsequently, near the light source, a wide variety of reflexes arise in different fish, depending on their lifestyle. If a defensive reflex occurs, the fish immediately swim away, but if they are schooling or feeding, the fish linger for a long time in the illuminated area.

(http://www.urhu.ru/fishing/ryby)

Light-sensitive cells are located on the side of the pigment membrane. Their processes, which are shaped like rods and cones, contain a light-sensitive pigment. The number of these photoreceptor cells is very large: there are 50 thousand of them per 1 mm 2 of the retina in a carp, 162 thousand in a squid, 16 in a spider, 400 thousand in a human. Through a complex system of contacts between the terminal branches of sensory cells and the dendrites of nerve cells, light stimuli enter the optic nerve. In bright light, cones perceive the details of objects and color: they capture long waves of the spectrum. Rods perceive weak light, but cannot create a detailed image: perceiving short waves, they are about 1000 times more sensitive than cones. The position and interaction of the cells of the pigment membrane, rods and cones changes depending on the illumination. In the light, pigment cells expand and cover the rods located near them; The cones are pulled towards the cell nuclei and thus move towards the light. In the dark, sticks are pulled towards the nuclei and are closer to the surface; the cones approach the pigment layer, and the pigment cells, which contract in the dark, cover them. The number of different types of receptors depends on the lifestyle of the fish. In diurnal fish, cones predominate in the retina, while in crepuscular and nocturnal fish, rods predominate: burbot has 14 times more rods than pike. Deep-sea fish that live in the darkness of the depths do not have cones, but the rods become larger and their number increases sharply - up to 25 million per 1 mm 2 of the retina; the likelihood of catching even weak light increases. Most fish distinguish colors. Some features in the structure of fish eyes are associated with the characteristics of life in water. They are ellipsoidal in shape and have a silvery shell between the vascular and the albumen, rich in guanine crystals, which gives the eye a greenish-golden sheen. The cornea of fish is almost flat (and not convex), the lens is spherical (and not biconvex) - this expands the field of view. The hole in the iris (pupil) can change its diameter only within small limits. Fish, as a rule, do not have eyelids. Only sharks have a nictitating membrane covering the eye like a curtain, and some herring and mullet have a fatty eyelid-transparent film covering part of the eye. The location of the eyes in most species on the sides of the head is the reason that fish have largely monocular vision, and the ability Binocular vision is limited. The spherical shape of the lens and its movement forward to the cornea provides a wide field of vision: light enters the eye from all sides. The vertical viewing angle is 150°, horizontal - 168...170°. But at the same time, the spherical shape of the lens causes myopia in fish. Their range of vision is limited and varies due to the turbidity of the water from several centimeters to several tens of meters. Vision over long distances becomes possible due to the fact that the lens can be pulled back by a special muscle - the falciform process, coming from the choroid of the bottom of the optic cup, and not due to changes in the curvature of the lens, as in mammals. With the help of vision, fish also orient themselves relative to objects located on the ground. Improving vision in the dark is achieved by the presence of a reflective layer (tapetum) - guanine crystals, underlying pigment. This layer transmits light to the tissues lying behind the retina, but reflects it and returns it to the secondary retina. This increases the ability of the receptors to use the light entering the eye. Due to the living conditions, the eyes of fish can change greatly. In cave or abyssal (deep-sea) forms, the eyes can be reduced and even disappear. Some deep-sea fish, on the contrary, have huge eyes that allow them to capture very weak light, or telescopic eyes, the collecting lenses of which the fish can place parallel and gain binocular vision. The eyes of some eels and larvae of tropical fish are carried forward on long projections (stalked eyes). The modification of the eyes of the four-eyed fish, which lives in the waters of Central and South America, is unusual. Its eyes are placed on the top of the head, each of them is divided by a partition into two independent parts: the upper fish sees in the air, the lower one in the water. The eyes of fish crawling onto land can function in the air. In addition to the eyes, the pineal gland (endocrine gland) and light-sensitive cells located in the tail, for example, in lampreys, perceive light. The role of vision as a source of information for most fish is great: when orienting during movement, searching for and capturing food, preserving the flock, during the spawning period (perception of defensive and aggressive postures and movements by rival males, and between individuals of different sexes, mating plumage and spawning “ceremonial”), in prey-predator relationships, etc. Carp sees at illumination of 0.0001 lux, crucian carp - 0.01 lux. The ability of fish to perceive light has long been used in fishing: fishing for light. It is known that fish of different species react differently to light of different intensities and different wavelengths, i.e. e. different colors. Thus, bright artificial light attracts some fish (Caspian sprat, saury, horse mackerel, mackerel) and repels others (mullet, lamprey, eel). Different species are also selective in their response to different colors and different light sources—overwater and underwater. All this forms the basis for organizing industrial fishing using electric light. This is how sprat, saury and other fish are caught. The organ of hearing and balance of fish. It is located at the back of the skull and is represented by a labyrinth. There are no ear openings, an auricle and a cochlea, i.e. the organ of hearing is represented by the inner ear. It reaches its greatest complexity in real fish: a large membranous labyrinth is placed in a cartilaginous or bone chamber under the cover of the ear bones. It consists of an upper part - an oval pouch (ear, utriculus) and a lower round pouch (sacculus). From the top. three semicircular canals extend from parts in mutually perpendicular directions, each of which is expanded into an ampulla at one end

The oval sac with the semicircular canals makes up the organ of balance (vestibular apparatus). The lateral expansion of the lower part of the round sac (lagena), which is the rudiment of the cochlea, does not develop further in fish. An internal lymphatic (endolymphatic) canal departs from the round sac, which in sharks and rays comes out through a special hole in the skull, and in other fish it blindly ends at the scalp. The epithelium lining the sections of the labyrinth has sensory cells with hairs extending into the internal cavity . Their bases are intertwined with branches of the auditory nerve. The cavity of the labyrinth is filled with endolymph, it contains “auditory” stones consisting of carbon dioxide (otoliths), three on each side of the head: in the oval and round sacs and lagena. On otoliths, like on scales, concentric layers are formed, therefore otoliths, especially the largest, are often used to determine the age of fish, and sometimes for systematic determinations, since their sizes and contours are not the same in different species. In most fish, the largest otolith is located in a round sac, but in cyprinids and some others, in the lagena. A sense of balance is associated with the labyrinth: when the fish moves, the pressure of the endolymph in the semicircular canals, as well as from the otolith, changes, and the resulting irritation is picked up by the nerve endings. When the upper part of the labyrinth with semicircular canals is experimentally destroyed, the fish loses the ability to maintain balance and lies on its side, back or belly. Destruction of the lower part of the labyrinth does not lead to loss of balance. The perception of sounds is associated with the lower part of the labyrinth: when the lower part of the labyrinth with a round sac and lager is removed, fish cannot distinguish sound tones, for example, when developing conditioned reflexes. Fish without the oval sac and semicircular canals, that is, without the upper part of the labyrinth, are amenable to training. Thus, it has been established that the sound receptors are the round sac and the lagena. Fish perceive both mechanical and sound vibrations with a frequency of 5 to 25 Hz by the lateral line organs, and from 16 to 13,000 Hz by the labyrinth. Some species of fish detect vibrations located at the boundary of infrasonic waves by the lateral line, labyrinth and skin receptors. Hearing acuity in fish is less than in higher vertebrates, and is not the same among different species: ide perceives vibrations whose wavelength is 25... 5524 Hz, silver crucian carp - 25...3840, eel - 36...650 Hz, and they pick up low sounds better. Sharks hear sounds made by fish at a distance of 500 m. Fish also pick up those sounds whose source is not in the water, but in the atmosphere, despite the fact that such sound is 99.9% reflected by the surface of the water and, therefore, penetrates into the water only 0.1% of the sound waves generated. In the perception of sound in carp and catfish fish, a large role is played by the swim bladder, connected to the labyrinth and serving as a resonator. Fish can also make sounds themselves. The sound-producing organs of fish are different. These are the swim bladder (croakers, wrasses, etc.), the rays of the pectoral fins in combination with the bones of the shoulder girdle (somas), jaw and pharyngeal teeth (perch and carp), etc. In this regard, the nature of the sounds is also different. They can resemble blows, clattering, whistling, grunting, grunting, squeaking, croaking, growling, crackling, rumble, ringing, wheezing, beeping, bird cries and chirping insects. The strength and frequency of sounds made by fish of the same species depends on gender, age , food activity, health, pain, etc. The sound and perception of sounds is of great importance in the life of fish. It helps individuals of different sexes find each other, maintain the flock, inform relatives about the presence of food, protect the territory, nest and offspring from enemies, and is a stimulator of maturation during mating games, i.e., it serves as an important means of communication. It is assumed that in deep-sea fish, dispersed in the darkness at oceanic depths, it is hearing, in combination with the lateral line organs and sense of smell, that ensures communication, especially since sound conductivity, which is higher in water than in air, increases at depth. Hearing is especially important for nocturnal fish and inhabitants of turbid waters. The reaction of different fish to extraneous sounds is different: when there is noise, some move away, others (silver carp, salmon, mullet) jump out of the water. This is used when organizing fishing. In fish farms, during the spawning period, traffic is prohibited near spawning ponds.

Endocrine glands

The endocrine glands are the pituitary gland, pineal gland, adrenal glands, pancreas, thyroid and ultimobronchial (subesophageal) glands, as well as the urohypophysis and gonads. They secrete hormones into the blood. The pituitary gland is an unpaired, irregular oval-shaped formation extending from the lower side of the diencephalon (hypothalamus) . Its outline, size and position are extremely varied. In carp, carp and many other fish, the pituitary gland is heart-shaped and lies almost perpendicular to the brain. In goldfish, it is elongated, slightly flattened laterally and lies parallel to the brain. In the pituitary gland, two main sections of different origin are distinguished: the cerebral (neurohypophysis), which makes up the inner part of the gland, which develops from the lower wall of the diencephalon as an invagination of the bottom of the third cerebral ventricle, and the glandular (adenohypophysis), formed from the invagination of the upper wall of the pharynx. The adenohypophysis is divided into three parts (lobes, lobes): main (anterior, located on the periphery), transitional (largest) and intermediate (Fig. 34). The adenohypophysis is the central gland of the endocrine system. In the glandular parenchyma of its lobes, a secret is produced containing a number of hormones that stimulate growth (somatic hormone is necessary for bone growth), regulate the functions of the gonads and thus affect puberty, affecting the activity of pigment cells (determine body color and, above all, the appearance of breeding plumage ) and increase the resistance of fish to high temperatures, stimulates protein synthesis, the functioning of the thyroid gland, and is involved in osmoregulation. Removal of the pituitary gland entails the cessation of growth and maturation. Hormones secreted by the neurohypophysis are synthesized in the nuclei of the hypothalamus and transported along nerve fibers to the neurohypophysis, and then enter the capillaries that penetrate it. Thus, it is a neutrosecretory gland. Hormones take part in osmoregulation and cause spawning reactions. A single system with the pituitary gland is formed by the hypothalamus, the cells of which secrete a secret that regulates the hormone-forming activity of the pituitary gland, as well as water-salt metabolism, etc. The most intensive development of the pituitary gland occurs during the period of transformation of the larva into a fry. In sexually mature In fish, its activity is uneven due to the biology of fish reproduction and, in particular, the nature of spawning. In fish that spawn at the same time, the secretion accumulates in the glandular cells almost simultaneously “after the secretion is excreted, by the time of ovulation the pituitary gland is emptied, and there is a break in its secretory activity. In the ovaries, by the time of spawning, the development of oocytes, prepared for spawning in a given season, ends. Oocytes are spawned in one go and thus constitute a single generation. In spawning fish, the secretion in the cells is not formed simultaneously. As a result, after the secretion is released during the first spawning, some cells remain in which the process of colloid formation has not completed. As a result, it can be released in portions throughout the spawning period. In turn, oocytes prepared for laying in a given season also develop asynchronously. By the time of the first spawning, the ovaries contain not only mature oocytes, but also those whose development has not yet been completed. Such oocytes mature some time after the hatching of the first generation of oocytes, i.e., the first portion of eggs. In this way, several portions of caviar are formed. Research on ways to stimulate the maturation of fish led almost simultaneously in the first half of our century, but independently of each other, Brazilian (Iering and Cardozo, 1934-1935) and Soviet scientists (Gerbilsky and his school, 1932-1934) to the development method of pituitary injections to producers to accelerate their maturation. This method made it possible to significantly control the process of fish maturation and thereby increase the scope of fish farming operations for the reproduction of valuable species. Pituitary injections are widely used in artificial breeding of sturgeon and carp fish. The third neurosecretory section of the diencephalon is the pineal gland. Its hormones (serotin, melatonin, adrenoglomerulotropin) are involved in seasonal changes in metabolism. Its activity is affected by illumination and daylight hours: when they increase, the activity of fish increases, growth accelerates, gonads change, etc. The thyroid gland is located in the pharynx, near the abdominal aorta. In some fish (some sharks, salmon) it is a dense paired formation consisting of follicles that secrete hormones; in others (perch, carp) glandular cells do not form a formed organ, but lie diffusely in the connective tissue. Secretory activity of the thyroid gland begins very early . For example, in sturgeon larvae, on the 2nd day after hatching, the gland, although not fully formed, exhibits active secretory activity, and on the 15th day, the formation of follicles is almost complete. Follicles containing colloid are found in 4-day-old stellate sturgeon larvae. Subsequently, the gland periodically secretes an accumulated secretion, and an increase in its activity is noted in juveniles during metamorphosis, and in mature fish in the pre-spawning period, before the appearance of the nuptial plumage. Maximum activity coincides with the moment of ovulation. The activity of the thyroid gland changes throughout life, gradually falling during the aging process, and also depending on the food supply of fish: underfeeding causes increased function. In females, the thyroid gland is more developed than in males, but in males it more active. The thyroid gland plays an important role in the regulation of metabolism, growth and differentiation processes, carbohydrate metabolism, osmoregulation, maintaining the normal activity of nerve centers, the adrenal cortex, and gonads. Adding a thyroid preparation to the feed accelerates the development of fry. When the function of the thyroid gland is impaired, a goiter appears. The sex glands - the ovaries and testes - secrete sex hormones. Their secretion is periodic: the largest amount of hormones is formed during the period of gonad maturity. The appearance of mating plumage is associated with these hormones. The hormones 17^-estradiol and esterone, localized mainly in the eggs, and less so in the ovarian tissue, were found in the ovaries of sharks and river eels, as well as in the blood plasma of sharks. Deoxycorticosterone and progesterone were found in male sharks and salmon. In fish, there is a relationship between the pituitary gland, thyroid gland and gonads. In the pre-spawning and spawning periods, the maturation of the gonads is directed by the activity of the pituitary gland and the thyroid gland, and the activity of these glands is also interconnected. The pancreas in bony fish performs a dual function - the glands of external (secretion of enzymes) and internal (secretion of insulin) secretion. The formation of insulin is localized in the islets of Langerhans , embedded in the liver tissue. It plays an important role in the regulation of carbohydrate metabolism and protein synthesis. Ultimobranchial (supraperibranchial, or subesophageal) glands are found in both marine and freshwater fish. These are paired or unpaired formations lying, for example in pikes and salmon, on the sides of the esophagus. Gland cells secrete the hormone calcitonin, which prevents the resorption of calcium from bones and thus prevents its concentration in the blood from increasing. Adrenal glands. Unlike higher animals, in fish the brain and cortex are separated and do not form a single organ. In bony fishes they are located in different parts of the kidney. The cortex (corresponding to the cortical tissue of higher vertebrates) is embedded in the anterior part of the kidney and is called interrenal tissue. The same substances are found in it as in other vertebrates, but the content of, for example, lipids, phospholipids, cholesterol, and ascorbic acid in fish is higher. Hormones of the cortical layer have a multifaceted effect on the vital functions of the body. Thus, glucocorticoids (cortisol, cortisone, 11-deoxycortisol are found in fish) and sex hormones take part in the development of the skeleton, muscles, sexual behavior, and carbohydrate metabolism. Removal of interrenal tissue leads to respiratory arrest before cardiac arrest. Cortisol is involved in osmoregulation. The adrenal medulla in higher animals and fish corresponds to chromaffin tissue, individual cells of which are scattered and kidney tissue. The hormone adrenaline they secrete affects the vascular and muscular systems, increases the excitability and force of heart pulsation, and causes dilation and constriction of blood vessels. An increase in the concentration of adrenaline in the blood causes a feeling of anxiety. The neurosecretory and endocrine organ in teleost fish is the urohypophysis, located in the caudal region of the spinal cord and involved in osmoregulation, which has a great influence on the functioning of the kidneys.

Venom content and toxicity of fish

Venom-bearing fish have a venom-bearing apparatus consisting of spines and poisonous glands located at the base of these spines (Mvoxocephalus scorpius during the spawning period) or in their grooves of spines and grooves of fin rays (Scorpaena, Frachinus, Amiurus, Sebastes, etc.).

The strength of the poisons varies: from the formation of an abscess at the injection site to respiratory and cardiac dysfunction and death (in severe cases of Trachurus damage). In our seas, the poisonous ones are the sea dragon (scorpion), stargazer (sea cow), sea ruffe (scorpionfish), stingray, sea cat, spiny shark Katran), sculpin, sea bass, nosari ruff, aukha (Chinese ruff), sea mouse (lyra), high-beam perch.

These fish are harmless when eaten.

Fish, the tissues and organs of which are poisonous in chemical composition, are classified as poisonous and should not be eaten. They are especially numerous in the tropics. The shark Carcharinus glaucus has a poisonous liver, and the shark Tetradon has poisonous ovaries and eggs. In our fauna, the caviar and peritoneum of the marinka Schizothorax and the osman Diptychus are poisonous; in the longhorned beetle Barbus and the khramuli Varicorhynus, the caviar has a laxative effect. The venom of poisonous fish affects the respiratory and vasomotor centers and is not destroyed by boiling. Some fish have poisonous blood (eels Muraena, Anguilla, Conger, lamprey, tench, tuna, carp, etc.). Poisonous properties appear when the blood serum of these fish is injected; they disappear when heated, under the influence of acids and alkalis.

Poisoning with stale fish is associated with the appearance in it of toxic waste products of putrefactive bacteria. Specific “fish poison” is formed in benign fish (mainly sturgeon and white fish) as a product of the vital activity of anaerobic bacteria Bacillus ichthyismi, close to B. botulinus. The effect of the poison is manifested when eating raw, including salted fish.

Close one eye! Now open and close the other one. What did you saw? It’s practically the same thing with both the right and left eyes, because with both eyes you look forward. Now imagine a fish doing the same. If she closes her right eye, she will see what is on the left side of her; if she closes her left eye, she will see what is on her right. But a fish cannot close its eyes - which means it looks both to the right and to the left at the same time! And he sees completely different pictures. How does a fish understand them?

Located on different sides of the head, the eyes of the fish are adapted for monocular vision, since the spherical lens is shifted far forward, towards the cornea itself (Fig. 1), rays penetrate into the eye not only from the front, but also from above and from the sides - and therefore the field of view There is a lot of fish!

Fig.1.

Counting together with eye movements, the visual angle covers 166-170° horizontally, and about 150° vertically; and binocular vision is only possible in a very limited field (approximately 130°). And it is in this field that the fish clearly distinguishes objects. The position of the fish's eyes is a determining factor in this regard. If a fish wants to look at an object, it is forced to quickly turn around so that it is in the field of view of both eyes - in a narrow cone-shaped binocular space (Fig. 2).

Fig.2.

The fish is able to see objects above the surface of the water through the so-called “visual window”. This window is equal to a circle on the surface of the water formed by an angle of 97.6° with the vertex located at the point where the fish is located (Fig. 3).

Fig.3.

Through this window, fish see from the zenith to the horizon in all directions. This hemispherical visual field contains all objects located above a plane tangent to the surface of the water at the edge of the window. But the distortion and brightness of objects are very different. Objects located directly above your head appear larger (they are perceived by the fish almost without distortion), and you should remember this when catching shy fish. As the object descends along the meridian of the air hemisphere towards the horizon, its image will decrease both in width and length and at the same time be distorted, although the linear distance from the fish to the object is unchanged. The object becomes more dimly visible due to the fact that the rays, forming an ever smaller angle with the surface of the water, are strongly reflected from the surface and only partially enter the fish’s eye. The phenomenon of light refraction also causes a discrepancy between the true and observed location of an object in space. In this case, the greatest discrepancy between them will be at an angle of incidence of the light rays of 45°, decreasing as it approaches 90°.

Unlike other animals, the fish's eye has an ellipsoidal shape and is equipped with a flat cornea. The refractive power of the eye depends not only on the curvature of the cornea and lens, but also on the properties of the material from which they are composed, and the cornea in fish, like in humans, is not capable of refracting light rays in water.

Most fish are nearsighted - they see well only at close distances - about 1 m, and beyond 10-12 m they cannot see anything at all. In the retina of bony fish there are special perceptive elements - cones and rods. Moreover, among diurnal fish, cones predominate, while among fish that obtain food at dusk and at night, rods abound: for example, the night burbot has 260 rods in the same area where the pike has only 18! In the light, the state of the retina changes: the cones move towards the light, and vice versa, at dusk the rods move towards the light.

In fish (as in humans), different concentrations of light-perceiving elements lead to the fact that they see clearly only the object specifically examined. Predatory fish that lie in wait for their prey need a very wide field of vision in order to clearly see a fairly large area, and such vision is not very suitable for them. However, here too, nature has found a way out - the light-perceiving devices of the eye are designed in such a way that they are capable of transmitting information to the brain not about the intensity of the light falling on them, but only about the nature of the change in illumination. As soon as there is even the slightest change in the illumination of the rods and cones, they immediately telegraph this to the brain and wait for the next changes to give the next telegram. And so all my life.

Most predatory fish have a very strong motor feeding reaction to the movement of food objects. Forms of protection of prey fish from predator fish are the formation of schools, immobility, etc. To escape from predators, peaceful fish must see approaching danger from afar, therefore the slightest, barely noticeable movement of large objects, their silhouettes, shadows and unclear flickers are well perceived by these fish and cause a defensive reaction in them. So when fishing, take into account these visual features of non-predatory fish and try not to scare them away with your scary look and equally scary shadow. By the way, it is this clearly expressed defensive reaction to the shadow that underlies the method of catching mullet with a matting.

When you're fishing with a spinner, live bait, or other moving bait, there's another important factor to consider. The perception of movement by fish can be measured in so-called optical moments, which are characterized by the fish's ability to perceive the intermittency of light. The human optical moment is 1/18-1/24 s. This means that when 18-24 identical objects per second pass through a person’s visual field, they merge together, taking the form of a stationary line. As this speed decreases, successively moving objects are perceived first as flickers and then as individual moving objects. Ichthyologists determine optical moments using a special optomotor unit. For example, in Black Sea fish, as well as bream and perch, they are half as fast as in humans (1/57-1/67 s), which means that compared to humans, fish are able to perceive twice as fast movements. In freshwater: minnow, tench, crucian carp, silver carp, pike and verkhovka, the optical moment is approximately twice as large (1/18-1/27 s). This diversity of optical moments in fish is apparently associated with different perceptions of movements. Small values of optical moments allow some “visual fish” to successfully feed on moving objects and avoid their enemies. Any moving object that is smaller than or equal to the size of the fish is a visual food signal, and a moving object that is larger is a visual defensive signal. Almost all fish react to a moving shadow, but the perception of movements and the nature of the responses depend on the lifestyle of the fish. This is associated with a more crude ability to perceive movements in freshwater sedentary fish - crucian carp and silver carp, which feed on stationary and sedentary objects. It is precisely small optical moments that can explain why, when fishing from boats or spinning rods, the hooks remain empty - the fish either do not notice the bait rushing by at high speed, or it has a deterrent effect on them, but you tried so hard!

Of course, you don’t need to take a calculator and computer with you when fishing; it’s better to take a closer look at how and what the fish eat.

It turns out that fish eyes are able to identify most geometric shapes. The choice of food baits by fish is significantly influenced by their shape. Ichthyologists used baits of approximately the same size in the following shapes: ball, cone, triangle, square, parallelepiped, worm-shaped, star, etc. All proposed shapes, with the exception of the star, were perceived positively by the fish. Probably, the unusual shape of the star scared them off, since even very hungry fish avoided grabbing it.

Do fish perceive color? Previously it was believed that distinguishing colors in water was impossible. But back in the middle of the 20th century. Karl Frisch successfully developed conditioned reflexes of a gudgeon to a certain color, always giving food in a red bowl while simultaneously laying out empty black, gray and white bowls. Very soon the minnows learned to swim straight to the red bowl. It has been proven that fish use cones for color vision.

Experiments on the study of color vision in fish have been continued by many ichthyologists and are still being carried out. Schiemenz found that fish perceive ultraviolet rays as colors, distinguishing them from others. If we remember that ultraviolet penetrates deeper than other rays, then the idea of complete darkness at depths up to 1500 m will not be correct. By the way, Herter trained fish not only for different colors, but also for a certain shape, and even for the letters R and L.

But these are all scientists. What do fishermen say? For example, perches take bait with a red worm more readily than with a white one, but beluga, on the contrary, are attracted to the white color. Previously, in the Caspian Sea there was poaching of beluga “on kalada”. Pieces of white oilcloth in the shape of a triangle were placed on large hooks. It is possible that the beluga mistakes the bait for a white shell and takes it. For a long time, fishermen have painted their nets in colors that are unnoticeable to fish.

Unfortunately, not all species of fish have been studied for the presence of color vision today, but it is known for sure that river lamprey, capelin, cod, haddock, pollock, striped catfish, sculpin, ruff flounder, mullet, anchovy, horse mackerel, and sea fish distinguish colors. and river burbot, red mullet, bream, pike, river perch, golden carp, tench, carp, river eel, eared perch, minnow and some other fish. It was also found that fish raised on different feeds prefer different colors of food.

By the way, do not forget that fish that find themselves on the shore do not lose their ability to see. An eel crawls from one body of water to another. Salmon or pike washed ashore direct their movements in such a way as to find themselves back in the reservoir. So be careful and don’t scatter fish along the shore, otherwise the prey will only wag its tail at you!