How do fish see? Can they see us? And who are we to them? Aliens, for whom the inhabitants of the underwater world are only a food product, or friendly aliens exploring their unknown and mysterious world. The life of underwater inhabitants is full of wonderful and amazing secrets.
The role of vision for underwater animals is extremely important. With its help, as with the help of other senses (smell, touch, hearing), fish receive information about the environment, and also provide contact between individuals of their species. Vision also determines the feeding activity of fish. Among predators, it has one goal - to find prey and hide from a stronger inhabitant of the sea in order to avoid attack and rush again in search of less protected and weaker individuals. And for defenseless herbivorous fish, nothing is more important than to get away from a predator and hide in a secluded place.
The optical properties of water do not allow the animal to see far. The lens in fish cannot change shape and adapt vision to distance. Its pungency depends on the transparency of the water. Fish can see well in clear water at a distance of no more than 1.5-2 meters, but they can distinguish objects within 12-15 meters.
Predatory fish living in flowing clear water (trout, grayling, asp) see better. Since the eyes of fish are located on the sides of the head and at some elevation above the surface of the body, their angle of vision is very large and, without turning, they can see with each eye not only in front, but also on the sides - up to 1700 horizontally and about 1500 horizontally. verticals.
The hammerhead shark, due to the strange shape of its head, sees clearly in all directions: not only what is happening in front of it, but also vertically - above and below, to the side and behind.
In muddy and low-transparent water, fish are able to navigate through second sight - the lateral line, a unique device that functions as a kind of radar that allows it to detect the slightest fluctuations in the water. The eyes of fish do not have eyelids, and they are constantly open. Sea water washes them and cleanses them of foreign impurities.
Now let's return to the question of whether the fish can see us. This is especially often asked by amateur fishermen. Not entirely good, but fish can also see the surface world. According to the law of refraction of light rays, they see relatively clearly, without distortion, objects located directly above their heads, for example, a boat or a bird flying over the water.
Obliquely incident rays are refracted. And the sharper the angle and lower the object, the more distorted it appears to the fish. For example, an angler standing on the shore is visible to the fish quite well. But if he sits down, the fish practically does not see him, especially in stormy weather.
When fishing for mullet with a lifting hatchery, a fish caught in a net trap clearly sees the wall blocking its path and strives to escape, trying to jump over it. Sometimes large mullet conduct initial reconnaissance by slightly jumping out of the water, assessing the height of the wall, and only then make a powerful jump.
Finding themselves not in their environment, on the shore, fish do not lose their ability to navigate. For example, an eel calmly crawls from one body of water to another. And try throwing a live, freshly caught large fish ashore: it will do everything to find itself in its native element. Pisces can not only see, but also remember what they see.
An amazing incident occurred off the coast of Puerto Rico. A large mako shark was shot with a hunting harpoon gun. Having made a dash towards the sea and freed herself from the arrow, she rushed to the shore. To the amazement of those present, she tried to grab the unlucky hunter standing on the shore, not paying attention to the people nearby.
And some fish have eyes that are specially adapted for observation not only in water, but also in the air. Anableps fish is a four-eyed fish native to the Amazon. Her eyes are divided into upper and lower chambers, equipped with special optics. The upper part of the eye is adapted for observation in the air, the lower part - in water. This fish perfectly sees both a mosquito in the air and a small crustacean in the water.
Predatory fish see much better than herbivores. They need keen vision when tracking and pursuing victims. The peculiarity of the visual apparatus of some fish allows them to divide the movement of escaping prey into separate phases and guess its direction and speed, which allows them to catch a fast and agile prey with a lightning-fast throw. Small schooling fish see much worse.
Research has confirmed that fish even distinguish the shape of an object, distinguish a square from a triangle, and a cube from a pyramid, which even some land animals cannot do.
Pisces can see color. Especially those living in the surface layers of water, where the sun's rays penetrate well. This has long been proven by numerous experiments and is confirmed by their rich body coloration with various color shades, especially during the spawning period. And fish brides have a more favorable attitude towards a male with a bright and variegated coloring - after all, they accept him based on his clothes.
But who knows what else fish females are guided by when choosing a partner for procreation. Many species of fish know by sight the “husbands” they have chosen for life together and do not allow a stranger to invade their lives and ruin their family happiness.
Color vision allows fish to adapt to their environment to protect themselves from predators. For example, fish that live on light pound have light colors, while those living among algae have striped camouflage clothing.
Well, some fish, such as flounder, change color literally on the move depending on the color of the soil and blend in with it so much that a predator, swimming over the hidden fish, does not notice it. However, blind fish, including flounder, do not change their color depending on the change in the color of the ground, and visual perception in this case remains fundamental.
Diurnal predator fish are sharper than others. These include pike, trout, and grayling. At night - pike perch, bream, catfish. They have light-sensitive elements in the retina of their eyes that perceive very weak light rays, which make it possible to distinguish the shadows of the victim in the dark.
Fish have adapted to navigate in constant darkness - in the deep-sea part of the ocean. The eyes, as a rule, are large and have a telescopic structure, allowing them to capture the slightest glimpses of light, usually emanating from the deep-sea inhabitants themselves.
Many of them have peculiar light organs - “flashlights”, built for convenience into some part of the body, for example, into the mouth. The hungry fish opens its mouth wide and the light automatically lights up. Small fish, attracted by the light, swim into the mouth, and the cunning predator immediately closes it. In some deep-sea fish, elongated processes emanating from the head “burn”, like antennas that perceive the voices of other underwater inhabitants - “friends” or “strangers”.
And others shine entirely, like Christmas tree decorations, in the light of burning multi-colored garlands. The researchers, who descended in the submersible to great depths, into the utter kingdom of darkness, were amazed at the wonderful colorful world that opened up before them. Sparkling ghosts floated in front of them, shimmering in multicolor.
What beauty hides from human sight in the endless depths of the ocean! I would like for the underwater inhabitants to be just a peace-loving alien exploring this mysterious world.
Vladimir KORKOSH, ichthyologist, journalist (Kerch).
We continue our traditional column Tips from experienced fishermen - we’ll tell you about the sensory organs of fish:
Navigation: About fish - organs, instincts
Vision
The eye of a fish is a fairly advanced optical device. It has no eyelids and is constantly open. In practice, fish in clear water can see no further than 10-12 m, and clear water only within 1.5 m. The angle of vision of fish is very large. Without turning their body, they can see objects with each eye vertically in a zone of about 150° and horizontally up to 170°. The fish sees objects located in front and to the sides well, somewhat worse from behind, but even when stationary it is able to view most of the environment. 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. 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 rough, the fish stops seeing the object altogether. Rays coming from the eye of the fish outside the cone shown in Fig. 1 are completely reflected from the water surface, and it appears mirror-like to the fish. It reflects the bottom, aquatic plants, and swimming fish. Rice. 1. Diagram of the visual angles at which the fish sees objects in the water
Rice. 1.2. Diagram of visual angles at which fish see objects above water
On the other hand, the peculiarities of the refraction of rays allow the fish to see seemingly hidden objects. Let's imagine a pond 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 (Fig. 2). Therefore, when fishing, it is always preferable to sit rather than stand, since the likelihood of getting into the field of view of a fish is much less.
The structural features of the fish eye, as well as other organs, depend primarily on the living conditions and their lifestyle. Rice. 2 Refraction of rays by human and fish vision
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 better vision is of paramount importance for finding prey.
Many of 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. These fish also have the ability to distinguish colors and even shades. It’s not for nothing that fishermen attract the attention of fish by decorating their hooks with colored hairs, most often red.
Fishermen know well that for successful fishing, the color of the lures used is not indifferent.
The ability to distinguish colors is developed differently in different fish. Fish living near the surface, where there is a lot of light, can distinguish colors better. Worse are those who live in the depths, where only part of the light rays penetrate. Pisces do not respond equally to artificial light. It attracts some, repels others. For example, a fire built on the bank of a river attracts, according to old fishermen, roach, burbot, and catfish. But eel and carp do not like light.
The visual characteristics of fish allow us to draw some conclusions that are useful for the fisherman. It is safe to say that a fish located at the surface of the water is not able to see a fisherman standing on the shore further than 10-12 m, and a fisherman sitting or wading - further than 5-6 m; The transparency of the water also matters. In practice, we can assume that if an angler does not see a fish in the water when he looks at a well-lit water surface at an angle close to 90°, then the fish does not see the angler. Therefore, camouflage makes sense only when fishing in shallow places or on top in clear water and when casting over a short distance. On the contrary, items of fishing equipment close to the fish - a leash, a sinker, a net, a float, a boat - should blend into the surrounding background.
Touch in fish
Touch or tactile sensitivity in fish is the main way they understand the world around them. The source of information in this case is touching objects, other fish, plants, and substrate. And it is obtained through tactile receptors, which are located differently in fish: in cartilaginous species - on parts of the body that are not protected by placoid scales (on the antennae of sawnose sharks, on the belly of stingrays); in bony species - throughout the body, but most concentrated on the fins, antennae, and lips.
Tactile receptors are located in the skin that covers the body of the fish, in the nasal sac (in the lining), in the oral cavity, in the thickness of its mucous membrane (including the pharyngeal and gill cavities). All of them are divided by experts into groups:
- rapidly adapting receptors:
- thermal Krause flasks and Meissner corpuscles, which perceive friction, movement, vibration, touch; they contain hairs, the displacement and bending of which conveys some information to the fish;
- Pacinian corpuscles, “responsible” in fish for the perception of high-frequency vibration.
- slow adapting receptors:
- Markel cells, which respond to local pressure and are capable of detecting spatially high differences in stimuli;
- Ruffini corpuscles, capable of detecting stretching of the outer integuments of the skin.
- free nerve endings that cover almost the entire surface of the body in fish;
- nerve endings on the head, which are the exit of the trigeminal nerve;
- nerve endings on the fins, caudal peduncle, body, which are the exit of the spinal nerves.
Nerve endings, in addition to purely tactile sensations, allow fish to “discriminate” temperature, pain and chemical characteristics.
Organs of touch
Ichthyology claims that in fish the tactile specialized function is performed by a whole set of “devices”: growths, outgrowths, free fin rays, fins, whiskers, rostrum. In addition, they often carry additional chemosensory taste buds, which expands their function in assessing the surrounding world and allows them to “take a closer look,” in particular, at fishing devices and baits.
Mustache
This type of receptor is an epidermal, tentacle-shaped outgrowth located on the head of the fish, most often around or near the mouth. Their length, number, and shape vary greatly among different fish species; The mustache can be stationary or movable. When a significant portion is lost or damaged, the receptors are regenerated. In the epidermis of the mustache skin, in addition to tactile receptors, there are many taste buds.
Such a wide range of “possibilities” of the whiskers indicates their importance in the life of fish and determines their lifestyle, behavior, and nutrition. They are especially needed in highly turbid waters, at depths where sunlight practically does not penetrate.
The structure and length of the whiskers influence the feeding ecology of fish. For example, long-whiskered and short-whiskered common crucian carp, in which the difference in the size of the whiskers is 1...2 cm, in conditions of food shortage, feed on various food items.
From observations useful for fishermen: if there are taste buds in the fish’s whiskers, it means they are more active in exploring the surrounding space when searching for food. This, for example, is inherent in many species of catfish, which prefer to feed on the bottom and, moreover, at dusk. Cod fish do the same, adding to the capabilities of the whiskers the functions of free fin rays.
Fins
The free rays present in the fins are among the main organs that provide fish with a sense of touch. They are found in the pectoral, pelvic and dorsal fins. The length of the rays varies; in some fish they can even exceed the length of the body.
In the rays, scientists have discovered sensory cells similar to those located on the chin barbels of fish. With such receptors, underwater inhabitants test bottom objects, assessing their possibility of use as food.
There are examples of free rays that can move. For example, in gurnards, their sector of movement reaches 180°, which allows the fish to feel a much larger area than it can inspect using vision.
Rostrums
This type of receptor is the part of the head located in front of the eyes. Like all others, they come in different sizes and perform different functions. For example, in fish that swim quickly, the rostrum is elongated and helps reduce water resistance; They also allow the existing tactile sensors to sense the flow of water and select the optimal direction of movement.
The network of lateral canals present on the rostrum informs the fish about the speed of movement. In sturgeons, electroreceptive organs are also located here; in shovelnose fish, in which the rostrum is thickened and equal in length to a third of the total length of the fish, they are equipped with ampullary receptors that can “report” the presence of individual planktonic organisms nearby or their accumulation.
In addition to sturgeon, other species of fish, using tactile receptors on the rostrum, search for food in the thickness or on the surface of the bottom. The rostrum is also used by some fish as a tool for obtaining food from the soil.
Dermal teeth and spawning growths
During the preparation period and during the spawning process, spawning growths act as the most popular tactile receptors. Dermal teeth (or odontodes) are scattered throughout the body of fish and are intended for testing food and controlling the flow of water.
In general, tactile sensations are more important for grass, bottom, and cave fish. According to observations, for example, catfish grab food only when the whiskers touch it. If the bait floats past, the predator often does not react to it. The importance of touch is emphasized by an experiment in which minnows and trout were blinded, but the fish did not die of hunger precisely because of the use of tactile sensations using different receptors.
Especially for lovitut.ru - V.A.N.
Hearing
It has long been known that fish react to sounds. A noise or sound can both scare and attract fish. Fishermen skillfully use both the curiosity and timidity of fish. Catfish are successfully caught by luring them by hitting the water with a special mallet - a “quok”. Fishermen often use noise to drive fish into their nets. It has been established that fish are able to detect sounds with a frequency ranging from 5 Hz to 13 kHz, i.e. in a wider range compared to humans (from 16 Hz to 13 kHz). Vibrations generated in the air do not reach the ears of fish well, because these waves are almost completely reflected from the water surface. You have probably observed that fish swimming in a river near the surface of the water do not respond to noise (even strong) from a distance of about 8-10 m. But any noise created in the water irritates the fish. This is explained by the fact that fish can hear sounds arising in water at a considerable distance. And some fishermen, without taking this into account, often lower their fishing rods, tanks with fish with a splash, or, even worse, trying to free themselves from a blade of grass on a spoon, they begin to forcefully whip it into the water.
Fish perceive sounds with a frequency of 16 to 13,000 vibrations per second through the auditory labyrinths in the head and through the skin. Considering the hearing capabilities of fish, when fishing you should try to be quiet, without creating noise that could scare away the fish and ruin your fishing for you and other anglers. Fish perceive mechanical and infrasonic vibrations with frequencies from 5 to 16 per second with the “sixth” sense organ, which will be discussed in detail in the next section.
Aquaria2.RU
It cannot be assumed that fish are not endowed with vision, that they do not hear, do not have a sense of smell and touch, and do not feel taste. Pisces have all of the five senses listed above, and they also have the corresponding organs of these senses. In addition, it is believed that fish have a sixth sense associated with the perception of vibrations and flow of water.
The eyes of fish are distinguished by peculiar features corresponding to the living conditions of this group of animals. Fish see only at close range; the average norm for their visibility is considered to be a distance of 1 meter; beyond 10–12 meters the fish see nothing at all. In a dense, low-transparency water environment, and their eyes are more advanced than those of fish, they cannot see far.
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 washed ashore directs its movements in such a way as to find itself again in the water element; The pike behaves the same way.
The eyes of the Anableps fish, found in the sea off the coast of Brazil, have a unique structure. The length of this fish is up to 20 centimeters. Its scientific name is “tetrophthalmus,” which in Russian means four eyes. The eyes of Tetrophthalmus are divided into two parts by a horizontal stripe (but there is only one lens). This fish usually swims on the surface of the water, the lower halves of the eyes are in the water, and the upper halves are in the air, and the fish can thus see objects both in the water and in the air.
The bulging eyes of the jumper fish also see both in water and in the air. Let's remember the splasher, or shooter, who accurately directs a stream of water at insects sitting on the coastal grass.
Fish that live at great depths, as well as in cave waters, have less perfect eyes, sometimes they have no organ of vision at all.
The lamprey, whose eyes seem so lifeless, responds well to light. I conducted observations of lampreys in the aquariums of the Saratov Biological Station. During the day, lampreys, usually crowded together, hang in the corners of aquariums, and from evening until dawn they rush and even jump out of the water. If you illuminate the aquarium at night, the lampreys begin to gather again and stick to the glass. But here's what's interesting. The lampreys in the aquarium did not react at all to attempts to attract their attention with dark and shiny objects that I rotated in front of the glass. It was possible to bring the lampreys out of their dormant state only by touching their body.
Do fish see colors? This question must be answered in the affirmative. It is no coincidence that anglers hang bunches of bright red threads on their spoons; Fish are also attracted by the shiny, silver or golden color of the spoon. Perches take bait with a red worm more readily than with a white one. Beluga is attracted to the color white. Previously, in the Caspian Sea there was beluga fishing “on kalada”. A piece of white oilcloth in the shape of a triangle was placed on large hooks. It is possible that the beluga mistakes the bait for a white shell and takes it. Such fishing was so intensive that it undermined the reserves of the most valuable sturgeon fish. Therefore, it was strictly prohibited in the Caspian and other seas.
Aquarium fish lovers know that it is possible to train fish to match certain colors.
Fishermen paint their nets in colors that are unnoticeable to fish.
The hearing apparatus in fish is poorly developed, and this gives rise to talk about the deafness of fish. But the fact that the organ of hearing in different species of fish is developed to varying degrees (in lampreys it is simpler, in bony fish it is more complex) indicates the improvement of the organ, and, undoubtedly, there is expediency in this. Pisces have the ability to hear.
Let us turn again to fishing practice. I saw how Koreans fish for pollock in the Sea of Japan. They catch this fish with hooks, without any bait, but they always hang trinkets (metal plates, nails, etc.) above the hooks. A fisherman, sitting in a boat, tugs on such a tackle, and the pollocks flock to the trinkets. Catching fish without trinkets does not bring good luck.
Screaming, knocking, shots above the water disturb the fish, but it is more fair to explain this not so much by the perceptions of the hearing aid, but by the ability of the fish to perceive the oscillatory movements of the water using the lateral line, although the method of catching catfish is “by shred”, by the sound produced by a special (hollowed out) blade and resembling the croaking of a frog, many are inclined to consider it evidence of hearing in fish. Catfish approach this sound and take the fisherman’s hook.
In L.P. Sabaneev’s classic book “Fishes of Russia,” unsurpassed in its fascination, bright pages are devoted to the method of catching catfish by sound. The author does not explain why this sound attracts catfish, but cites the opinion of fishermen that it is similar to the voice of catfish, which seem to cluck at dawn, calling for males, or to the croaking of frogs, which catfish love to feast on. In any case, there is reason to assume that the catfish hears.
In the Amur there is a commercial fish, silver carp, known for being a school fish and jumping out of the water when it makes noise. You will go out on a boat to the places where the silver carp are found, hit the water or the side of the boat with an oar, and the silver carp will not be slow to respond: several fish will immediately jump out of the river noisily, rising 1–2 meters above its surface. Hit it again, and the silver carp will jump out of the water again. They say that there are cases when silver carp jumping out of the water sink the small boats of the Nanai. Once on our boat, a silver carp jumped out of the water and broke the window. This is the effect of sound on silver carp, apparently a very restless (nervous) fish. This fish, almost a meter long, can be caught without a trap.
Pond (domestic) fish approach the sound of a bell.
But there are more convincing facts that speak in favor of hearing in fish. Many fish make their own sounds. In the South China Sea, fishermen have long learned to eavesdrop on fish. The fisherman lowers his head over the side of the boat, plunges it into the water about 20 centimeters and listens to the underwater sounds. Experienced fishermen distinguish fish by their voice. Fish of one species grumble, of another they chirp, of a third they hum, etc. Schools of herring chirp like chicks, sprat make noise like the wind in the forest. Hearers claim that fish of the same species make a different sound when feeding than when migrating.
The fish sea eagle (up to 2 meters long), sea raven and drummer, living off the coast of tropical and subtropical seas (they are also found in the Mediterranean and Black Seas) make peculiar sounds underwater. The large drummer fish (about 1.5 meters long), living in the western part of the Atlantic Ocean, received this name for a reason: the sounds it makes resemble the beat of a drum. The scientific name of this fish is “pogonias chromis”, which translated from Greek into Russian means bearded creaker. This fish has small antennae on its chin, and the sound it makes seems to some like a squeak.
Flounder lives in tropical waters and makes a sound reminiscent of a harp or a bell. The Black Sea seacock trigla, similar to a goby, makes an “oo-hrr-oo” sound. The origin of this sound is explained by the friction of the bones of the gill covers against each other. Trigla is also remarkable in that it can move (walk) along the bottom of the sea, using the three rays of the pectoral fins as legs. These same three fins are credited with the role of organs of touch and even organs of taste. Some species of trigla have luminescent organs.
Further studies of fish will undoubtedly reveal many other species whose representatives make sounds.
Scientists have sophisticated equipment for marine research. There are devices that allow you to find schools of fish, determine their approximate numbers, etc. An echo sounder has now become a universal device that is used by both research and fishing vessels. Time will pass, and a device will appear that will allow one to perceive and record the sounds of the underwater kingdom, and then no one will be able to claim that eternal silence reigns in the world of fish.
The ability to make and perceive sounds has a certain significance in the life of fish. Just as geese and swans communicate with each other through voice during migration, fish may also signal each other during migration, when they herd to spawn or search for feeding grounds.
The olfactory organs of fish are well developed. In sharks and rays, the nasal openings are located on the underside of the head, in bony fish - on the upper side, in front of the eyes. The water entering the nasal openings washes the nasal fossa, the walls of which are penetrated by the branches of the olfactory nerve.
The sense of smell plays a significant role in the life of fish. We carried out such an experiment. The blinded burbot's nostrils were closed and food was brought very close, but the fish did not detect it. When the nostrils were opened, the same blind burbot quickly found food, even located 30 centimeters from it. Here's another experience. Different food was placed in the corners of the aquarium, and the fish, using its sense of smell, found the food it needed.
Sharks have a particularly well developed sense of smell. The smell of waste from whale factories attracts them from quite considerable distances. If you damage the olfactory lobes of the brain in a shark's head, it will lose its sense of smell. Sharks are caught with hooks skewered with strong-smelling fried pieces of seal meat.
Feel the fish and taste. If a shark is eager for a fried piece of seal meat or fish, then it recognizes this piece as tasty. The beluga grabs a white oilcloth attached to a hook because he mistakes it for an edible shell. The organs of taste in fish are papillae, buds on the lips and body. If you throw food that is unsuitable for a fish, it may grab it in a hurry, but then quickly spit it out.
Fishermen know which fish like which food and prepare the appropriate bait. On the Neva, and in other places, bream is caught well with bait in the form of buckwheat porridge. Ide is caught on soaked peas, catfish on frogs, and so on.
Everyone knows that fish have a sense of touch - all fish instantly react to the lightest touch on their body. You look at a pike sleeping at the bottom of the river, and it seems that it is dead, but as soon as you touch the tail or head with a rod, the pike instantly disappears.
When hunting with a light beam, fish staying near the bottom are clearly visible. The fisherman brings the spear very close to the body of the fish, but it does not detect any alarm until the moment the spear touches it. By the way, it must be said that such hunting is prohibited, and I remembered it only to prove the ability of fish to feel the touch of solid objects on their body and respond to these touches. Fish also use their fins and whiskers to touch.
We have already said that fish also have a sixth, the so-called lateral sense. Fish feel vibrations in the water, the movement of other fish in the neighborhood, and feel approaching objects. This sense allows fish to swim freely both at night and in muddy water.
The main organ of the lateral sense is the lateral line, which in most fish is a series of perforated scales along which runs a canal with sensitive buds located in it. In the lowly developed frilled shark, the lateral line runs in the form of a groove from head to tail; in other sharks, like bony sharks, the groove has turned into a closed channel with pores for communication with the external environment.
The lateral sense organs in some fish larvae are represented by appendages on the body. The picture shows a larva of a common gudgeon, in which the lateral sense organs - in the form of delicate appendages - are located on the head. They disappear with age.
A blinded pike was placed in an aquarium, but thanks to its lateral line, it quickly overtook its prey and swallowed it. When the lateral line was damaged, the pike lost the ability to detect prey.
In some fish, the lateral line is expressed only on the anterior scales. Smelt has several dozen transverse rows of scales on the sides of its body, while the lateral line runs only along 4–15 front scales. In minnows, the lateral line runs intermittently; in some fish it is strongly curved. There are fish that have two, three or even more lateral lines on each side, sometimes they are branched. In a number of fish, the functions of this organ are performed by numerous grooves, tubules, which are located on the head and are a continuation of the lateral line. According to some scientists, the dense network of head sensory canals made the lateral line in herring redundant, and it gradually disappeared in them. An interesting and clear example of the evolution of an organ!
The sensitive tubules on the head are clearly visible if the skin is carefully removed from the head. Water pressure is transmitted to the fish through mucus contained in the lateral line and head canals. It has been proven that sound vibrations are not perceived by the lateral line. The “sixth sense” of fish needs further research.
‹ Peaceful and predatory fishTopAge and growth of fish ›
Sixth Sense
The main organ of this sense in fish is the lateral line. This organ is found only in fish and amphibians that constantly live in water. The lateral line is a canal that usually runs along the body from head to tail. The canal contains sensory buds, connected to the external environment, to the nerves and to the brain through tiny holes located in the scales. The lateral line perceives even the slightest water vibrations and helps fish determine the strength and direction of the current, catch reflected water currents, feel the movement of a neighbor in the school, and disturbances on the surface. Using their “sixth” sense, fish can swim at night in muddy water without bumping into underwater objects or each other. It is not without reason that an experienced spinning fisherman pays attention not only to the appearance of the spoon and its “game”, but also to the nature of the vibrations it creates. Even special spinners are used - acoustic ones. The lateral line also makes it possible to capture those vibrations that are transmitted to the water from the outside - as a result of soil shaking, impacts on the water, or a blast wave. Fish feel such vibrations with much greater sensitivity than vibrations in the air. Therefore, experienced fishermen are careful not to knock on the boat, walk along the shore without stomping, but are not afraid to talk loudly.
Predatory fish also use the lateral line as a locator, through which they monitor the movement of the prey. The lateral line helps peaceful fish to detect the enemy in a timely manner and distinguish it from its relatives.
Organs of touch, smell and taste. In addition to the “sixth” sense, touch and smell help fish navigate in the water. These two senses help the fish in its search for food. A well-developed sense of smell, the organs of which are the nasal pits, divided into two parts (the front pair of holes serves for water entry, and the back one for exit), allows fish to sense the appearance of unusual or familiar dissolved substances in the aquatic environment, even in negligible quantities . The organs of touch in some fish, such as carp, are located almost throughout the body. But most often they are located near the mouth. In burbot, the organ of touch is the antennae on the lower lip. The catfish has two long, movable whiskers. Pisces are good at distinguishing between tasty and tasteless, sweet and sour and salty. The taste organs are located in the mouth and pharyngeal cavity. In some individuals they come out of the mouth and onto the surface of the body: in carp - on the mustache, in catfish and burbot - on the lips. Thus, the fisherman must keep in mind that fish cannot be seduced by just any “dish”; it must also look attractive in appearance and have a good smell and taste. Table 1.1 Legend: xxx - the main organ involved in finding food; x x - an organ that is always involved in finding food: x - an organ that is sometimes involved in finding food; 0 - organ absent or not involved in finding food
The fish's senses include: vision, hearing, lateral line, electroreception, smell, taste and touch. Let's look at each one separately.
Nervous system and sensory organs of fish
1. The nervous system of fish is represented by the brain and spinal cord
. The brain is divided into the following sections: forebrain, diencephalon, midbrain, cerebellum and medulla oblongata. Twelve cranial nerves, grouped in pairs, extend from the brain.
2. At the forebrain
there is no division into hemispheres, and accordingly, there is almost no cortex. At its anterior end are the olfactory lobes.
3. From intermediate
and
the midbrain,
the optic nerves go to the eyes. The midbrain of most fish is small. It contains the centers of visual reflexes.
4. Cerebellum
responsible for the movements of the fish, it is well developed.
5. Medulla
responsible for the functioning of the digestive system, the functioning of the respiratory center, heart and other organs.
Sense organs
1. Olfactory organs
- one nostril in cyclostomes and paired nostrils in all other fish, from which openings lead into the olfactory cavities, which are not connected, as is typical for fish, with the oral cavity. How do fish smell in water? The nostril is divided by a septum into two halves, water flows into one and exits through the other. It is at this moment that the fish has time to analyze the smell and determine in which direction the food is located.
2. Organs of touch
- body coverings, sensitive rays of fins and whiskers. Sturgeon have very funny whiskers, and catfish have phenomenal whiskers - thick and long.
3. Organs of taste
- taste buds growing on the lips, in the mouth and even on the antennae.
4. Organs of vision
- large eyes, which, alas, see poorly; already a couple of meters away the picture becomes blurred. For most fish, the doctor would prescribe glasses for myopia. But the angle of vision of fish is large, up to 170 degrees with one eye, and they distinguish colors perfectly. Daytime predators such as trout or pike see best. Some nocturnal fish have adapted to see in the dark; catfish, for example, have special nerves for this. Deep-sea fish have almost lost their eyes in the process of evolution.
5. Hearing organs
- the inner ear located in the skull. Fish do not have an external ear at all as it is unnecessary, because water conducts sound well, and fish feel it through the bones of the skull. This is why fishermen are so sensitive to loud sounds near the water.
6. Organs of balance
in the form of three semicircular canals are also part of the inner ear. The channels are paired, just like the hearing organ.
7. Side line
- an interesting organ of fish, something between the organs of touch and hearing. On the sides of the body, under the scales, there are channels with sensitive cells that detect the direction of movement and the strength of the water current (seismosensory value), as well as infrasound (low frequencies). Using the lateral line, fish can determine at what distance from them other fish, food, and various objects are located.
8. swim bladder
, first of all, guarantees buoyancy, thanks to the gases filling it. But in addition to this, it can participate in the breathing process and produce sounds. Yes, fish can make noise and even “talk” - they chatter their teeth, rub their fins against each other, make sounds by moving their swim bladder.
Do you want to pass the exam with flying colors? Click here - preparation for the Unified State Exam in biology (Moscow)
Organ of vision
Vision
- one of the main sense organs in fish. The eye consists of a round shaped lens that has a hard structure. It is located near the cornea and allows you to see at a distance of up to 5 m at rest, maximum vision reaches 10-14 m.
The lens captures many light rays, allowing you to see in several directions. Often the eye has an elevated position, so it receives direct rays of light, oblique, as well as from above, below, and from the sides. This significantly expands the fish’s field of vision: in the vertical plane up to 150°, and in the horizontal plane up to 170°.
Monocular vision
– the right and left eyes receive a separate image. The eye consists of three membranes: the sclera (protects from mechanical damage), the vascular (supplies nutrients), and the retinal (provides light perception and color perception due to the system of rods and cones).
Organ system
Digestive
The digestive system begins with the mouth. Perch and other predatory bony fish have numerous small, sharp teeth on their jaws and many bones in their mouths that help them capture and hold prey. There is no muscular tongue. Through the pharynx into the esophagus, food enters the large stomach, where it begins to be digested under the influence of hydrochloric acid and pepsin. Partially digested food enters the small intestine, where the ducts of the pancreas and liver empty. The latter secretes bile, which accumulates in the gallbladder.
At the beginning of the small intestine, blind processes flow into it, due to which the glandular and absorptive surface of the intestine increases. Undigested residues are excreted into the hindgut and removed through the anus.
Respiratory
The respiratory organs - gills - are located on four gill arches in the form of a row of bright red gill filaments, covered on the outside with numerous thin folds, increasing the relative surface of the gills.
Water enters the fish's mouth, is filtered through the gill slits, washes the gills, and is thrown out from under the gill cover. Gas exchange occurs in numerous gill capillaries, in which blood flows towards the water washing the gills. Fish are able to absorb 46-82% of oxygen dissolved in water.
Opposite each row of gill filaments are whitish gill rakers, which are of great importance for the nutrition of fish: in some they form a filtering apparatus with a corresponding structure, in others they help retain prey in the oral cavity.
Blood
The circulatory system consists of a two-chambered heart and blood vessels. The heart has an atrium and a ventricle.
excretory
The excretory system is represented by two dark red ribbon-like buds, lying below the spinal column almost along the entire body cavity.
The kidneys filter waste products from the blood in the form of urine, which passes through two ureters into the bladder, which opens outward behind the anus. A significant part of the toxic decomposition products (ammonia, urea, etc.) are excreted from the body through the gill filaments of fish.
Nervous
The nervous system looks like a hollow tube thickened in front. Its anterior end forms the brain, which has five sections: the forebrain, diencephalon, midbrain, cerebellum and medulla oblongata.
The centers of different sense organs are located in different parts of the brain. The cavity inside the spinal cord is called the spinal canal.
Hearing organ
Hearing aid
(inner ear or labyrinth) located in the back of the skull, includes two compartments:
the upper oval and round lower sacs
.
The oval sac contains three semicircular canals - this is an organ of balance; endolymph flows inside the labyrinth; in cartilaginous fish it connects with the environment through the excretory duct; in bony fish it ends blindly. The organ of hearing in fish is combined with the organ of balance.
The inner ear is divided into three chambers, each containing the otolith (part of the vestibular apparatus that responds to mechanical irritation). The auditory nerve ends inside the ear, forming hair cells (receptors); when the position of the body changes, they are irritated by the endolymph of the semicircular canals and help maintain balance.
The perception of sounds is carried out due to the lower part of the labyrinth - a round sac. Fish are able to detect sounds in the range of 5Hz – 15kHz. The hearing aid includes the lateral line (allows you to hear low-frequency sounds) and the swim bladder (acts as a resonator, connected to the inner ear through the Weberian apparatus
, consisting of 4 bones).
Pisces are myopic animals
, often move in muddy water, with poor lighting; some individuals live in the depths of the sea, where there is no light at all. What sense organs and how do they allow one to navigate in water under such conditions?
Features of the organization of bony fishes (Osteichthyes)
The organ of hearing and balance in bony fish, like cartilaginous fish, is represented only by the inner ear, enclosed in a cartilaginous capsule, the outer walls of which ossify. The membranous labyrinth, or the inner ear itself, is formed by three well-developed semicircular canals lying in mutually perpendicular planes, extending from the oval sac (vestibular apparatus or organ of balance); the underlying round sac has a more or less clearly defined hollow outgrowth - lagena - and serves as the organ itself hearing The thin endolymphatic duct extending from the round sac ends blindly. In the cavity of the lagena, round and oval sacs lie otoliths, or auditory pebbles; they are formed by crystals of lime carbonate, held together by organic matter (by their layering, visible on thin sections, the age of the fish can be determined in many species). The principles of operation of the organ of hearing and balance are described above. In some bony fishes, a connection between the swim bladder and the membranous labyrinth occurs: the blind processes of the swim bladder adjoin the membrane-covered windows of the perilymphatic cavity (some perciformes, codfishes) or a Weberian apparatus is formed - a system of bones connecting the wall of the swim bladder with the perilymphatic cavity of the inner ear (cypriniformes, catfishes). ). Thanks to this, the membranous labyrinth serves as a receptor that detects changes in pressure in the swim bladder, and the swim bladder acts as a resonator and thereby increases hearing acuity. Bony fish perceive sound waves with frequencies ranging from 16 to 12,000 Hz. The receptor is the sensitive fields of the lagena and the round sac, and possibly the oval sac. Low-frequency sounds no higher than 500-600 Hz, apparently, can also be perceived by the lateral line organs. It should be recalled that in water sounds travel at a much higher speed than in air (about 1500 m/s versus 330 m/s) and over long distances. Therefore, sound orientation for aquatic animals, including fish, is very important. The sound conductivity of fish body tissues is close to the sound conductivity of water, and therefore the perception of sounds is possible with a relatively simple structure of the hearing organ.
Blind fish (Astyanax fasciatus)
In recent decades, it has become clear that the popular expression “dumb as a fish” is not true. Fish produce a variety of sounds that are perceived by individuals of the same and other species as signals of a certain meaning. Mechanical or nonspecific sounds that occur during various actions of the fish (swimming, breathing, eating) also have a signaling value. The sounds of the jaws when grasping prey and when grinding food attract other individuals of their species and predators; the sounds of feeding of predatory fish cause a defensive reaction in peaceful fish: flight, hiding, compaction of the school, etc. The sound of fluttering or “cries of pain” of the captured fish also attracts predators fish. Sounds specially produced by fish in a certain situation have a more specific species-specific meaning: when meeting partners during the breeding season (spawning signals, including the call of an individual of the other sex, recognition and stimulation of the release of reproductive products), warning signals, and threats when protecting laid eggs or protecting their own territories, etc. These specific sound signals can be very diverse. Creaking and grinding sounds are produced when the free bone rays of the fins, jaw bones and gill cover, pectoral fin girdle, etc. rub against each other at random.
The sounds produced with the help of the swim bladder are especially varied: they resemble drumming, clapping, whistling, grumbling, clucking, buzzing, moaning, etc. In the toadfish (batrach-shaped) on the outer wall of the heart-shaped swim bladder there are flat drum muscles, and the bladder cavity is divided by a dense diaphragm with a hole in the middle; makes sounds similar to grunting and steamship whistles. In terapons (perciformes), the drum muscles are attached to the occipital region of the skull and to the walls of the anterior part of the swim bladder, the sounds resemble clapping or drumming. Low grumbling sounds are produced by grenadiers, whose ribbon-like tympanic muscles lie on the sides of the swim bladder. Sound vibrations of the walls of the swim bladder can cause vibrations of the ossicles of the Weberian apparatus, the bones of the pectoral fin girdle, or rhythmic beats of the fin rays on the body. The mechanisms of sound in gobies, beluga and a number of other fish have not yet been clarified. The frequencies of sounds produced by fish lie in the range of 20-12,000 Hz, i.e., within the sensitivity of their hearing aid. The most diverse acoustic signals are characteristic of twilight and bottom-dwelling fish, fish with a complex population structure.
Thus, bony fishes have a variety of sensory organs. When navigating and searching for food, many receptors are almost always used. Thus, a violation of body position, for example, when a wave hits, is perceived by the eyes, the lateral line, the semicircular canals and the sensitive fields of the round and oval sacs (the areas to which the otoliths are adjacent), the swim bladder and the tactile corpuscles. When searching for moving prey, vision, lateral line organs and electrical organs are used, smell and touch help to find motionless food, and the capture and swallowing of food is controlled by vision and gustatory and tactile bodies located on the antennae and in the oral cavity.
Behavior and lifestyle. The behavior and associated population structure of bony fishes is quite complex. The richness of the unconditional reflex (innate) basis of the nervous activity of fish is expressed in complex instincts that ensure the search and acquisition of food, reproduction (spawning signals, selection of optimal places for spawning, various forms of care for offspring), migration, protection of individual areas or school organization , ensuring the development of large territories. Bony fish are capable of developing conditioned reflexes to colors, shapes and sizes of objects, sounds and other stimuli. All this determines the existence of certain and quite different population structures among different species. Complex forms of fish behavior are associated not only with the medulla oblongata and midbrain, but also with the striatal bodies of the forebrain. Thus, cichlids (perciformes), after removal of the forebrain, recognize individuals of the other sex, study a new territory, but cannot lay eggs and fertilize them, and lose the ability to unite in schools. In Hemichromis fish, the ability to guard eggs was not restored even 19 months after damage to the striatum.
Moon fish (Mola mola)
Territorial behavior is accompanied by the formation of various intrapopulation groups. Their initial form, apparently, is a “brood” - juveniles hatched from one clutch. The newly hatched larvae do not pay attention to each other, but after 2-3 days they usually get closer and repeat the movements of their neighbors, forming a single flock with coordinated behavior. This is facilitated by imitative behavior, based on the special signal “school” coloring inherent in the juveniles of many species - a distinct pattern or contrasting colored spots - which serves as identification landmarks. “Broods” of fry usually soon unite into large schools (elementary populations), consisting of fish that have developed together and have a similar physiological state and size. Such groupings often persist until puberty.
When moving in a school, fish adapt to each other in a certain way, providing a hydrodynamically favorable arrangement. The orderly placement of fish in a school is sometimes preserved during rest. The advantages of the school life of the so-called “peaceful” fish are undoubted: the school quickly finds accumulations of food and more easily detects the approach of an enemy; when the latter appears, the fish gather in such a dense group that it is difficult for even a large predator to tear off the prey, or, conversely, they scatter, disorienting the predator. Raider predators form “dispersed schools”, in which individuals or groups of several fish stay separated, but within the limits of “visibility” (visual or acoustic). This formation makes it easier to search for moving prey, attack and capture it. Many species of fish live in schools throughout their lives (herring, cod, carp, perch, etc.). Others unite during feeding and spawning migrations, but break up into small groups in food pastures and spawning grounds, where females often occupy separate areas for spawning, sometimes protected even after laying eggs by either a female (Pacific salmon) or a male (some tropical catfish, etc.) .). Freshwater predators such as catfish and pike, and a number of bottom-dwelling marine fish (anglerfishes, moray eels from eels, sculpin gobies from scorpionfishes, etc.) lead a solitary lifestyle.
When there is a lack of food in a reservoir, cannibalism often occurs - eating its own eggs and young. In some cases, it may even become the norm. In some lakes of Western Siberia, large individuals of common perch feed mainly on small perches, which in turn live off plankton - food that is not available to large perches. This makes it possible for the population to exist in water bodies where there is no other food for adult individuals.
Particularly complex intraspecific and interspecific relationships are characteristic of fish inhabiting tropical reservoirs and coral reefs. They are accompanied by a huge variety of colors and patterns, the development of sound signaling and display behavior, complex forms of mating behavior and bizarre hermaphroditism, caring for offspring (building nests, protecting eggs and young). Such an intraspecific (population) organization regulates the use of space with its vital resources. An example of the complication of relationships in species-rich biocenoses of tropical seas is the existence of small “cleaner fish” that collect parasites from the skin, surface of the pharynx and gills of larger fish – “patients”. The latter sometimes gather at the habitats of the “cleaners” in large groups, cartoonishly reminiscent of patients patiently waiting in the “doctor’s” waiting room. The cleaners themselves are usually brightly colored, which prevents attacks on them. One of these cleaners, the fish Labroides dimidiatus, which lives in the tropical Pacific Ocean, is a quickly and reversibly reversible hermaphrodite, capable of changing from male to female or back within a few minutes. They live in groups consisting of a head - a large male and a harem of females, among which large individuals dominate over small ones. The male, by active behavior, prevents the transformation of females into males, but when he dies, the dominant female immediately turns into a male, taking his place (Robertson, 1972). The relationship between cleaners and the large fish they serve has led to the emergence of a kind of mimicry, when small predators, resembling cleaners in shape and color, penetrate the gill cavities of deceived “patients”, tearing out pieces of gills.
Peruvian sardine (Sardinops sagax)
Species with a solitary lifestyle are often characterized by protective coloring and powerful weapons (spines, sharp rays of fins, sometimes with poisonous glands at the base, etc.); they usually have special sound signals associated with calling a female and protecting the territory.
Features of the lifestyle and behavior of fish belonging to various orders are described above. Regardless of the ecological appearance or systematic affiliation, the life of a fish always consists of alternation in a certain sequence of events, which in their totality form a biological cycle, closely related to seasonal changes in living conditions. It consists of breeding, feeding, preparation for the winter period and wintering, after which the new breeding season begins. Individual stages of the life (seasonal) cycle of fish are highlighted when describing nutrition, reproduction and other biological phenomena.
An important element of the annual life cycle of many fish species are migrations - movements with changes in habitats. Migrations can be active or passive. In the first case, the fish actively move in the chosen direction, sometimes overcoming strong currents and even rapids (for example, salmon). Passive migration uses the force of the current. Both forms of migration are usually combined: active - in adults, passive - in larvae and juveniles (migration of larvae of herring, eel, etc.). Passive migration also occurs in some sedentary pelagic fish living in areas of circular warm currents (sunfish, etc.).
During active migrations, fish navigate using all their senses. Chemical and temperature perceptions are thought to be especially important. Although fish are able to distinguish even small, fractions of a degree, temperature differences, the main guide seems to be the chemical sense. Adult eels swim in the direction of increasing salinity, and salmon swim in the direction of decreasing salinity. As mentioned above, when entering a river, fish orient themselves using chemical memory, which has retained the smell of the “native” river from the larval period. Observations of the behavior of schools of Pacific salmon migrating to the sea suggested that the choice of the general direction to the native shore is carried out using solar orientation or celestial navigation (the assumption needs to be verified).
In the life of many fish, migrations of different types replace each other. After spawning, making feeding migrations, the fish move to “pastures” rich in food. Some species remain more or less sedentary in these feeding areas until the next breeding cycle, while others constantly move in search of food. With the onset of the next breeding period, spawning migrations begin. Many freshwater and some marine fish of northern and temperate latitudes undergo wintering migrations after feeding. At wintering sites, fish survive the winter period in a state of minimal activity. In fresh water bodies, wintering places are usually the deepest areas - “pits”. In the lower reaches of the Urals, Volga and other Caspian rivers, sturgeon, roach, bream, carp and pike perch spend the winter in “pits”. The fish “stand” motionless, close to each other, sometimes in several layers. Anchovy, which feeds and spawns in the Sea of Azov, goes to the Black Sea for the winter in the fall. Far Eastern flounders in the Peter the Great Bay area feed in coastal areas of the sea, and during wintering they concentrate in a few areas at depths of about 100-150 m; they choose areas with positive temperatures and bury themselves in the silt, sometimes in several layers.
The beginning of wintering migrations is determined by the physiological state of the fish (the amount of accumulated fat, the appearance of “cold” enzymes, etc.) and changes in external conditions (temperature, salinity, oxygen content). In the absence of fat reserves, wintering migration may not take place. Thus, anchovy, which has a fat content of less than 14%, does not migrate from the Sea of Azov even with sharp drops in water temperature, with a fat content of 14-17% it begins to migrate with a temperature difference of 9-14 ° C, and with a fat content of about 22% it migrates together even at slight decrease in temperature. Sometimes mature populations leave for the winter, and immature individuals continue to feed throughout the winter (bream, pike perch, etc.).
Cleaner wrasse (Labroides dimidiatus)
The dynamics of fish numbers reflects the interaction of their populations with the environment. Its character is determined by many factors: the life expectancy of individuals of a given species, the nature and rate of their reproduction, food supply, mortality rates and variability of environmental factors (fluctuations in water level, temperature and oxygen content, changes in the power and direction of sea currents, etc.). In monocyclic species, which reproduce only once, at the end of life, the numbers are usually less stable and subject to greater fluctuations than in long-lived polycyclic species. The stability of numbers depends on the availability of food; Enemies and food competitors have a significant influence. Due to the greater stability of physicochemical conditions in the aquatic environment, especially in the seas, compared to land, fluctuations in the number of fish occur with a smaller amplitude than in many terrestrial animals. But freezing of spawning grounds in harsh winters has a catastrophic effect on individual populations of Far Eastern salmon, and the rubbing of caviar by floating ice has a catastrophic effect on the yield of herring in the Sea of Okhotsk.
Recently, human economic activity has had an increasing impact on the dynamics of fish numbers: fishing is increasing, pollution of water bodies by industrial and other waste is increasing, the construction of hydroelectric power stations is changing the hydrological regime, etc.
The frequency and amplitude of fluctuations in the number of individuals in populations varies widely. Thus, the catches of Pacific halibut - N. hippoglossus for the period 1925-1947. fluctuated by a factor of two, and catches of the Pacific sardine - Sardinops sagax in 1937-1957. varied from 2 million centners to zero. A high number of pink salmon entering the rivers of the Pacific coast usually occurs every year, and for Atlantic salmon - once every 10-11 years.
Fishing, by thinning out the population, leads to a “rejuvenation” of its age composition: the proportion of slowly growing older age groups decreases, and improved nutrition leads to accelerated growth and earlier maturation of young fish. Thus, fishing in a certain amount has a positive effect on the reproduction of the population, increasing the intensity of reproduction and the growth rate of fish. However, if the catch exceeds the norm (varies for different species and regions), it reduces the herd of breeders and the population begins to decline. Therefore, for each species and for a given reservoir, it is important to determine optimal catch rates that ensure consistently high catches by maintaining an increased reproductive capacity of the population.
Literature: N. P. Naumov, N. N. Kartashev. Zoology of vertebrates. Lower chordates, jawless fish, amphibians. Moscow "Higher School", 1979
Side line
First of all, this is the side line
- the main sensory organ in fish. It is a channel that runs under the skin along the entire body and branches in the head area, forming a complex network. It has holes through which it communicates with the environment. Inside there are sensitive kidneys (receptor cells) that perceive the slightest changes around.
This way they can determine the direction of the current, navigate the area at night, and sense the movement of other fish, both in a school and of predators approaching them. The lateral line is equipped with mechanoreceptors; they help aquatic inhabitants to dodge pitfalls and foreign objects, even in poor visibility.
The lateral line can be complete (located from the head to the tail), incomplete, or can be completely replaced by other developed nerve endings
.
If the lateral line is injured, the fish will no longer be able to survive for long, which indicates the importance of this organ. The lateral line of fish is the main organ of orientation
Electroreception
Electroreception
– a sensory organ of cartilaginous fish and some bony fish (electric catfish). Sharks and rays sense electric fields using ampullae of Lorenzini - small capsules filled with mucous contents and lined with specific sensitive cells, located in the head area and communicate with the surface of the skin using a thin tube.
Very susceptible and capable of sensing weak electric fields (the reaction occurs at a voltage of 0.001 mKV/m).
Thus, electrosensitive fish can track down prey hidden in the sand thanks to the electric fields that are created when muscle fibers contract during breathing.
Lateral line and electrosensitivity
– these sense organs are characteristic only of fish!
General characteristics of the Pisces class and the organization of their nervous system
Telencephaloncartilaginous and bony fish are fundamentally different from each other in structure, development and level of functional organization, so they must be analyzed separately.
The telencephalon (cerebral hemispheres) of cartilaginous fish is built according to the inverted type, i.e. contain lateral medullary ventricles, although the extent of their development varies among groups of sharks and rays. In the hemispheres of sharks and rays, two main areas are distinguished: dorsal (pallial) and ventral (subpallial), homologous to the corresponding areas of the brain of terrestrial vertebrates (Fig. 11).
Rice. 11. Structure of the hemispheres of the telencephalon of the shark Squalus acanthyas L. (after: Obukhov, 1999, with modifications). A-E – levels of brain slices, DP, MP, LP – dorsal, medial and lateral pallium, Str – striatum (subpallium), Spt – septum, Tol – olfactory tubercle, Vlat – lateral ventricle (cerebral cavity), NC – central nucleus, arrows – boundaries of hemisphere areas.
It should be noted that in a number of shark species, a true cortical layer with differentiated forms of neurons is formed in the dorsal pallium, similar to those in the neocortex of mammals and birds!
The high level of cytoarchitectonic and neural differentiation of a number of parts of the telencephalon of cartilaginous fish correlates with a high level of functional organization of the telencephalon in certain species of sharks and rays. All major sensory systems are projected into the hemispheres of their brain, and the biochemical composition of neuronal membranes is similar to that of mammals. The systems of afferent and efferent projections are also similar. The formation in the central nervous system of a number of cartilaginous fish of structures similar in level of morpho-functional organization to higher vertebrates is a manifestation of the evolutionary phenomenon of “phylogenetic advance”.
This phenomenon is associated with the appearance during evolution in individual representatives of a certain group of animals of characteristics that go beyond the “typical” characteristics of the group, which reflects the mosaic nature of evolution.
In general, the direction in which the central nervous system developed in a number of cartilaginous fish species can be considered evolutionarily progressive
(Obukhov, 1999).
Among bony fishes, ray-finned fishes are the only group of vertebrates whose telencephalon is built according to the everted type (Fig. 12).
The dorsal part of the hemisphere is subject to the process of eversion. According to one classification, it is divided into a number of cytoarchitectonic zones: medial, dorsal, dorsolateral, lateral and central. The ventral (subpallial) region is also divided into a number of zones. In connection with the peculiarities of embryogenesis of the telencephalon of ray-finned fish, the question of homology of their hemispheres with the structures of the inverted type of telencephalon is difficult. Some researchers propose direct homology of brain zones of the two types, others consider it impossible to make any comparisons, since they consider the telencephalon of ray-finned fish as a special line in the evolution of the vertebrate brain. Still others, and they are the majority, based on modern data on the morphology, histochemistry and connections of the telencephalon of vertebrates and taking into account the peculiarities of the processes of inversion and eversion, believe that a solution to this problem can be found. Thus, zone Dp is considered as a possible homologue of the lateral pallium, zones Dl and Dd - the medial and dorsal pallium of terrestrial vertebrates, respectively. The caudal parts of zone Dm and part of zone Dc are compared with the striatum, noting that other parts of these zones include components of the dorsal pallium. The rostral sections of the medial zone are homologated with part of the amygdala. The ventral zones Vd and Vv are compared with the region of the septal nuclei, the Vl zone - with the olfactory tubercle, and the caudal sections Vs, Vp, Vi - with part of the amygdala.
Among the huge number of species and groups of ray-finned fish, there are different levels of differentiation of the hemispheres: from the most simply structured hemisphere in multi-finned and sturgeon fish, to the more complex structure of the hemispheres in a number of higher bony fish. There is a clear evolutionary line of development of the telencephalon of ray-finned fish: Chondrostei – Holostei – Teleostei (Fig. 13).
Rice. 13. Schemes of the cytoarchitectonic structure of the hemispheres of a number of species of ray-finned fish (A) and a fragment of the neural structure of the telencephalon of carp (B) (after: Obukhov, 1975; Nikonorov, Obukhov, 1983). 1 – Polypterus palmas L., 2 – Aciperser baeri Br., 3 – Lepomis punctatus, 4 – Salmo salar L., 5 – Ictalurus punctatus L. DL, DC – zones of the dorsal region of the hemisphere of the carp Ciprinus carpio L., ext, d, rn – fusiform, horizontal and radial neurons, af, ef – afferent and efferent fibers.
An analysis of the neural structure of the telencephalon hemispheres of various representatives of ray-finned fish showed that the general level of its organization is quite low. The bulk of pallium neurons is represented by varieties of one – allodendrite class of neurons. These are multipolar radial neurons located predominantly in the deep layers of the peripheral zones of the pallium and in the central zone, as well as fan-shaped and horizontal neurons concentrated in the superficial layers of the zones (Fig. 13 and Fig. 14).
The degree of dendritic branching does not exceed 3-4 classes; the axon often departs not from the neuron body, but from the initial segment of one of the dendritic trunks. Cells combine the characteristics of associative and projection elements, since some of their axon collaterals branch within a given zone, while others - long projection branches extend beyond the zone and even the hemisphere region. In most other vertebrates (both higher and lower), populations of pallium neurons are divided into subpopulations of associative interneurons and projection neurons. In the ventral, subpallial region of the hemispheres, neural differentiation is even weaker—leptodendritic type neurons predominate here. In ray-finned fish, highly differentiated short-axon stellate neurons, which are a criterion for a high level of organization of nerve centers, were not found in the pallium and subpallium.
In general, in the evolutionary series of ray-finned fish (Chondrostei – Holostei – Teleostei) there are no significant changes in the level of neural differentiation of the hemispheres, which made it possible to put forward a hypothesis about a special, evolutionarily conservative
Pathways of brain development in ray-finned fish. This is confirmed by data on the physiology, communication system and behavior of these fish.
Olfactory organ
Smell
carried out using cilia located on the surface of special bags. When the fish smells the smell, the sacs begin to move: they contract and expand, capturing odorous substances. The nose includes 4 nostrils, sent out by many sensory cells.
With their sense of smell they easily find food, relatives, and a partner for the spawning period. Some individuals are able to signal danger by releasing substances to which other fish are sensitive. It is believed that the sense of smell for aquatic inhabitants is more important than vision.
