What are the physiological characteristics of migratory fish. Possibilities of rearing anadromous fish in brackish water. Abiotic factors of water bodies

Rice. Fish scale shape. a - placoid; b - ganoid; c - cycloid; d - ctenoid

Placoid - the most ancient, preserved in cartilaginous fish (sharks, rays). It consists of a plate on which a spine rises. Old scales are discarded, new ones appear in their place. Ganoid - mainly in fossil fish. The scales are rhombic in shape, closely articulated with each other, so that the body is enclosed in a shell. Scales do not change over time. The scales owe their name to ganoin (dentine-like substance), which lies in a thick layer on the bone plate. Among modern fish, armored pikes and multifins have it. In addition, sturgeons have it in the form of plates on the upper lobe of the caudal fin (fulcra) and scutes scattered over the body (a modification of several merged ganoid scales).
Gradually changing, the scales lost ganoin. Modern bony fish no longer have it, and the scales consist of bony plates (bone scales). These scales can be cycloid - rounded, with smooth edges (cyprinids) and ctenoid with a serrated trailing edge (percids). Both forms are related, but the cycloid, as a more primitive one, is found in low-organized fish. There are cases when, within the same species, males have ctenoid scales, and females have cycloid scales (flounders of the genus Liopsetta), or even scales of both forms are found in one individual.
The size and thickness of the scales in fish vary greatly - from microscopic scales of an ordinary eel to very large, palm-sized scales of a three-meter long barbel that lives in Indian rivers. Only a few fish do not have scales. In some, it merged into a solid, immovable shell, like a boxfish, or formed rows of closely connected bone plates, like seahorses.
Bone scales, like ganoid scales, are permanent, do not change and only increase annually in accordance with the growth of the fish, and distinct annual and seasonal marks remain on them. The winter layer has more frequent and thin layers than the summer one, so it is darker than the summer one. By the number of summer and winter layers on the scales, one can determine the age of some fish.
Under the scales, many fish have silvery crystals of guanine. Washed from scales, they are a valuable substance for obtaining artificial pearls. Glue is made from fish scales.
On the sides of the body of many fish, one can observe a number of prominent scales with holes that form the lateral line - one of the most important sense organs. The number of scales in the lateral line -
In the unicellular glands of the skin, pheromones are formed - volatile (odorous) substances released into the environment and affecting the receptors of other fish. They are specific to different species, even closely related ones; in some cases, their intraspecific differentiation (age, sex) was determined.
In many fish, including cyprinids, the so-called fear substance (ichthyopterin) is formed, which is released into the water from the body of a wounded individual and is perceived by its relatives as a signal announcing danger.
Fish skin regenerates quickly. Through it, on the one hand, a partial release of the end products of metabolism occurs, and on the other hand, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play a large role in life). The skin also plays an important role as a receptor surface: it contains thermo-, baro-, chemo- and other receptors.
In the thickness of the corium, the integumentary bones of the skull and pectoral fin belts are formed.
Through the muscle fibers of the myomers connected to its inner surface, the skin participates in the work of the trunk and tail muscles.

Muscular system and electrical organs

The muscular system of fish, like other vertebrates, is divided into the muscular system of the body (somatic) and internal organs (visceral).

In the first, the muscles of the trunk, head and fins are isolated. Internal organs have their own muscles.
The muscular system is interconnected with the skeleton (support during contraction) and the nervous system (a nerve fiber approaches each muscle fiber, and each muscle is innervated by a specific nerve). Nerves, blood and lymphatic vessels are located in the connective tissue layer of muscles, which, unlike the muscles of mammals, is small,
In fish, like other vertebrates, the trunk muscles are most developed. It provides swimming fish. In real fish, it is represented by two large strands located along the body from head to tail (large lateral muscle - m. lateralis magnus) (Fig. 1). This muscle is divided by a longitudinal connective tissue layer into dorsal (upper) and abdominal (lower) parts.

Rice. 1 Musculature of bony fish (according to Kuznetsov, Chernov, 1972):

1 - myomers, 2 - myosepts

The lateral muscles are divided by myosepts into myomers, the number of which corresponds to the number of vertebrae. Myomeres are most clearly visible in fish larvae, while their bodies are transparent.
The muscles of the right and left sides, contracting alternately, bend the caudal section of the body and change the position of the caudal fin, due to which the body moves forward.
Above the large lateral muscle along the body between the shoulder girdle and tail in sturgeons and teleosts lies the rectus lateral superficial muscle (m. rectus lateralis, m. lateralis superficialis). In salmon, a lot of fat is deposited in it. The rectus abdominis (m. rectus abdominalis) stretches along the underside of the body; some fish, such as eels, do not. Between it and the direct lateral superficial muscle are oblique muscles (m. obliguus).
The muscle groups of the head control the movements of the jaw and gill apparatus (visceral muscles). The fins have their own muscles.
The greatest accumulation of muscles also determines the location of the center of gravity of the body: in most fish it is located in the dorsal part.
The activity of the trunk muscles is regulated by the spinal cord and cerebellum, and the visceral muscles are innervated by the peripheral nervous system, which is excited involuntarily.

A distinction is made between striated (acting largely voluntarily) and smooth muscles (which act independently of the will of the animal). The striated muscles include the skeletal muscles of the body (trunk) and the muscles of the heart. Trunk muscles can contract quickly and strongly, but soon get tired. A feature of the structure of the heart muscles is not the parallel arrangement of isolated fibers, but the branching of their tips and the transition from one bundle to another, which determines the continuous operation of this organ.
Smooth muscles also consist of fibers, but much shorter and do not exhibit transverse striation. These are the muscles of the internal organs and the walls of blood vessels, which have peripheral (sympathetic) innervation.
Striated fibers, and therefore muscles, are divided into red and white, which differ, as the name implies, in color. The color is due to the presence of myoglobin, a protein that readily binds oxygen. Myoglobin provides respiratory phosphorylation, accompanied by the release of a large amount of energy.
Red and white fibers are different in a number of morphophysiological characteristics: color, shape, mechanical and biochemical properties (respiratory rate, glycogen content, etc.).
Red muscle fibers (m. lateralis superficialis) - narrow, thin, intensively supplied with blood, located more superficially (in most species under the skin, along the body from head to tail), contain more myoglobin in the sarcoplasm;
accumulations of fat and glycogen were found in them. Their excitability is less, individual contractions last longer, but proceed more slowly; oxidative, phosphorus and carbohydrate metabolism is more intense than in whites.
The heart muscle (red) has little glycogen and a lot of enzymes of aerobic metabolism (oxidative metabolism). It is characterized by a moderate rate of contractions and tires more slowly than white muscles.
In wide, thicker, light white fibers m. lateralis magnus myoglobin is small, they have less glycogen and respiratory enzymes. Carbohydrate metabolism occurs predominantly anaerobically, and the amount of energy released is less. Individual cuts are fast. Muscles contract and fatigue faster than red ones. They lie deeper.
The red muscles are constantly active. They ensure long-term and uninterrupted functioning of the organs, support the constant movement of the pectoral fins, ensure the bending of the body when swimming and turning, and the continuous work of the heart.
With fast movement, throws, white muscles are active, with slow movement, red ones. Therefore, the presence of red or white fibers (muscles) depends on the mobility of the fish: "sprinters" have almost exclusively white muscles, in fish that are characterized by long migrations, in addition to the red lateral muscles, there are additional red fibers in the white muscles.
The bulk of the muscle tissue in fish is made up of white muscles. For example, in asp, roach, sabrefish, they account for 96.3; 95.2 and 94.9% respectively.
White and red muscles differ in chemical composition. Red muscles contain more fat, while white muscles contain more moisture and protein.
The thickness (diameter) of the muscle fiber varies depending on the type of fish, their age, size, lifestyle, and in pond fish - on the conditions of detention. For example, in a carp grown on natural food, the diameter of the muscle fiber is (µm): in fry - 5 ... 19, underyearlings - 14 ... 41, two-year-olds - 25 ... 50.
The trunk muscles form the bulk of fish meat. The yield of meat as a percentage of the total body weight (meatiness) is not the same in different species, and in individuals of the same species it varies depending on sex, conditions of detention, etc.
Fish meat is digested faster than the meat of warm-blooded animals. It is often colorless (perch) or has shades (orange in salmon, yellowish in sturgeon, etc.), depending on the presence of various fats and carotenoids.
The bulk of fish muscle proteins are albumins and globulins (85%), in total, 4 ... 7 protein fractions are isolated from different fish.
The chemical composition of meat (water, fats, proteins, minerals) is different not only in different species, but also in different parts of the body. In fish of the same species, the amount and chemical composition of meat depend on the nutritional conditions and the physiological state of the fish.
During the spawning period, especially in migratory fish, reserve substances are consumed, depletion is observed and, as a result, the amount of fat decreases and the quality of meat deteriorates. In chum salmon, for example, during the approach to spawning grounds, the relative mass of bones increases by 1.5 times, skin - by 2.5 times. Muscles are hydrated - the dry matter content is reduced by more than two times; fat and nitrogenous substances practically disappear from the muscles - the fish loses up to 98.4% of fat and 57% of protein.
Features of the environment (primarily food and water) can greatly change the nutritional value of fish: in swampy, muddy or oil-polluted water bodies, fish have meat with an unpleasant odor. The quality of meat also depends on the diameter of the muscle fiber, as well as the amount of fat in the muscles. To a large extent, it is determined by the ratio of the mass of muscle and connective tissues, which can be used to judge the content of full-fledged muscle proteins in the muscles (compared to defective proteins of the connective tissue layer). This ratio varies depending on the physiological state of the fish and environmental factors. In the muscle proteins of bony fish, proteins account for: sarcoplasms 20 ... 30%, myofibrils - 60 ... 70, stroma - about 2%.
All the variety of body movements is provided by the work of the muscular system. It mainly provides the release of heat and electricity in the body of the fish. An electric current is formed when a nerve impulse is conducted along a nerve, with a contraction of myofibrils, irritation of photosensitive cells, mechanochemoreceptors, etc.
Electric Organs

The structure and physiological characteristics of fish

table of contents

Body shape and methods of movement

The skin of fish

Digestive system

Respiratory system and gas exchange (New)

Circulatory system

Nervous system and sense organs

Endocrine glands

Poisonousness and poisonousness of fish

The shape of the body of fish and the ways of movement of fish

The shape of the body should provide the fish with the opportunity to move in water (an environment much denser than air) with the least expenditure of energy and at a speed corresponding to its vital needs.
The shape of the body that meets these requirements has developed in fish as a result of evolution: a smooth body without protrusions, covered with mucus, facilitates movement; no neck; a pointed head with pressed gill covers and clenched jaws cuts through the water; the fin system determines the movement in the right direction. According to lifestyle, up to 12 different types of body shape are distinguished

Rice. 1 - garfish; 2 - mackerel; 3 - bream; 4 - moon fish; 5 - flounder; 6 - eel; 7 - fish-needle; 8 - herring king; 9 - slope; 10 - hedgehog fish; 11 - bodywork; 12 - grenadier.

Arrow-shaped - the bones of the snout are elongated and pointed, the body of the fish has the same height along the entire length, the dorsal fin is related to the caudal and is located above the anal, which creates an imitation of the plumage of an arrow. This form is typical for fish that do not travel long distances, stay in ambush and develop high speeds of movement for a short period of time due to the push of the fins when throwing at prey or avoiding a predator. These are pikes (Esox), garfish (Belone), etc. Torpedo-shaped (it is often called spindle-shaped) - characterized by a pointed head, rounded, oval-shaped body in cross section, thinned caudal peduncle, often with additional fins. It is characteristic of good swimmers capable of long-term movements - tuna, salmon, mackerel, sharks, etc. These fish are able to swim for a long time, so to speak, at a cruising speed of 18 km per hour. Salmon are capable of jumping two to three meters when overcoming obstacles during spawning migrations. The maximum speed that a fish can develop is 100-130 km per hour. This record belongs to the sailfish. The body is symmetrically compressed laterally - strongly laterally compressed, high with a relatively short length and high. These are fish of coral reefs - bristle teeth (Chaetodon), thickets of bottom vegetation - angelfish (Pterophyllum). This body shape helps them to easily maneuver among obstacles. Some pelagic fish also have a symmetrically laterally compressed body shape, which needs to quickly change position in space to disorientate predators. The moonfish (Mola mola L.) and bream (Abramis brama L.) have the same body shape. The body is asymmetrically compressed from the sides - the eyes are shifted to one side, which creates an asymmetry of the body. It is characteristic of demersal sedentary fish of the Flounder-like order, helping them to camouflage themselves well at the bottom. In the movement of these fish, an important role is played by the wavy bending of the long dorsal and anal fins. The body is flattened in the dorsoventral direction - strongly compressed in the dorsal-abdominal direction, as a rule, the pectoral fins are well developed. Sedentary bottom fish have this body shape - most rays (Batomorpha), monkfish (Lophius piscatorius L.). The flattened body camouflages the fish in bottom conditions, and the eyes located on top help to see the prey. Eel-shaped - the body of the fish is elongated, rounded, having the appearance of an oval in a cross section. The dorsal and anal fins are long, there are no pelvic fins, and the caudal fin is small. It is characteristic of bottom and bottom fish, such as eels (Anguilliformes), which move by bending their bodies laterally. Ribbon-shaped - the body of the fish is elongated, but unlike the eel-shaped form, it is strongly compressed from the sides, which provides a large specific surface area and allows the fish to live in the water column. The nature of their movement is the same as that of eel-shaped fish. This body shape is typical for saber fish (Trichiuridae), herring king (Regalecus). Macro-shaped - the body of the fish is high in the front, narrowed from the back, especially in the tail section. The head is large, massive, the eyes are large. It is characteristic of deep-sea sedentary fish - macrourus-like (Macrurus), chimeric (Chimaeriformes). Asterolepid (or body-shaped) - the body is enclosed in a bony shell, which provides protection from predators. This body shape is characteristic of benthic inhabitants, many of which are found in coral reefs, such as boxfish (Ostracion). The spherical shape is characteristic of some species from the Tetraodontiformes order - the ball fish (Sphaeroides), the hedgehog fish (Diodon), etc. These fish are poor swimmers and move with the help of undulating (wave-like) movements of the fins over short distances. When threatened, fish inflate the intestinal air sacs, filling them with water or air; at the same time, the spikes and spines on the body are straightened, protecting them from predators. The needle-shaped body shape is characteristic of marine needles (Syngnathus). Their elongated body, hidden in a bone shell, imitates the leaves of the zoster, in the thickets of which they live. The fish lack lateral mobility and move with the help of the undulating (wave-like) action of the dorsal fin.
Often there are fish whose body shape resembles simultaneously different types of forms. To eliminate the unmasking shadow on the belly of the fish that occurs when illuminated from above, small pelagic fish, such as herring (Clupeidae), sabrefish (Pelecus cultratus (L.)], have a pointed, laterally compressed abdomen with a sharp keel. Large mobile pelagic predators have mackerel (Scomber), swordfish (Xiphias gladius L.), tuna (Thunnus) - usually do not develop a keel.Their method of defense is speed of movement, not camouflage.In demersal fish, the cross-sectional shape approaches an isosceles trapezium facing large base down, which eliminates the appearance of shadows on the sides when illuminated from above.Therefore, most demersal fish have a wide flattened body.

SKIN, SCALES AND LUMINOSIS

Rice. Fish scale shape. a - placoid; b - ganoid; c - cycloid; g - ctenoid

Placoid - the most ancient, preserved in cartilaginous fish (sharks, rays). It consists of a plate on which a spine rises. Old scales are discarded, new ones appear in their place. Ganoid - mainly in fossil fish. The scales are rhombic in shape, closely articulated with each other, so that the body is enclosed in a shell. Scales do not change over time. The scales owe their name to ganoin (dentine-like substance), which lies in a thick layer on the bone plate. Among modern fish, armored pikes and multifins have it. In addition, sturgeons have it in the form of plates on the upper lobe of the caudal fin (fulcra) and scutes scattered over the body (a modification of several merged ganoid scales).
Gradually changing, the scales lost ganoin. Modern bony fish no longer have it, and the scales consist of bony plates (bone scales). These scales can be cycloid - rounded, with smooth edges (cyprinids) and ctenoid with a serrated trailing edge (perch). Both forms are related, but the cycloid, as a more primitive one, is found in low-organized fish. There are cases when, within the same species, males have ctenoid scales, and females have cycloid scales (flounders of the genus Liopsetta), or even scales of both forms are found in one individual.
The size and thickness of the scales in fish vary greatly - from microscopic scales of an ordinary eel to very large, palm-sized scales of a three-meter long barbel that lives in Indian rivers. Only a few fish do not have scales. In some, it merged into a solid, immovable shell, like a boxfish, or formed rows of closely connected bone plates, like seahorses.
Bone scales, like ganoid scales, are permanent, do not change, and only increase annually in accordance with the growth of the fish, and distinct annual and seasonal marks remain on them. The winter layer has more frequent and thin layers than the summer one, so it is darker than the summer one. By the number of summer and winter layers on the scales, one can determine the age of some fish.
Under the scales, many fish have silvery crystals of guanine. Washed from scales, they are a valuable substance for obtaining artificial pearls. Glue is made from fish scales.
On the sides of the body of many fish, one can observe a number of prominent scales with holes that form the lateral line - one of the most important sense organs. The number of scales in the lateral line -
In the unicellular glands of the skin, pheromones are formed - volatile (odorous) substances released into the environment and affecting the receptors of other fish. They are specific to different species, even closely related ones; in some cases, their intraspecific differentiation (age, sex) was determined.
In many fish, including cyprinids, the so-called fear substance (ichthyopterin) is formed, which is released into the water from the body of a wounded individual and is perceived by its relatives as a signal announcing danger.
Fish skin regenerates quickly. Through it, on the one hand, a partial release of the end products of metabolism occurs, and on the other hand, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play a large role in life). The skin also plays an important role as a receptor surface: it contains thermo-, baro-, chemo- and other receptors.
In the thickness of the corium, the integumentary bones of the skull and pectoral fin belts are formed.
Through the muscle fibers of the myomers, connected to its inner surface, the skin participates in the work of the trunk and tail muscles.

Muscular system and electrical organs

The muscular system of fish, like other vertebrates, is divided into the muscular system of the body (somatic) and internal organs (visceral).

Rice. 1 Musculature of bony fish (according to Kuznetsov, Chernov, 1972):

1 - myomers, 2 - myosepts

Electric organs are peculiarly altered muscles. These organs develop from the rudiments of striated muscles and are located on the sides of the fish body. They consist of many muscle plates (there are about 6000 in electric eel), converted into electrical plates (electrocytes), interbedded with gelatinous connective tissue. The bottom of the plate is negatively charged, the top is positively charged. Discharges occur under the influence of impulses of the medulla oblongata. As a result of discharges, water decomposes into hydrogen and oxygen, therefore, for example, in the overseas reservoirs of the tropics, small inhabitants accumulate near electric fish - mollusks, crustaceans, attracted by more favorable breathing conditions.
Electric organs can be located in different parts of the body: for example, in the sea fox stingray - on the tail, in the electric catfish - on the sides.
By generating electric current and perceiving lines of force,
distorted by objects on the way, the fish navigate in the stream, detect obstacles or prey from a distance of several meters, even in muddy water.
In accordance with the ability to generate electric fields, fish are divided into three groups:
1. Strongly electric types - they have large electric organs that generate discharges from 20 to 600 and even 1000 V. The main purpose of the discharges is attack and defense (electric eel, electric ramp, electric catfish).
2. Weakly electric species - have small electric organs that generate discharges with a voltage of less than 17 V. The main purpose of the discharges is location, signaling, orientation (many mormirids, hymnotids, and some rays that live in the muddy rivers of Africa).
3. Non-electric species - do not have specialized organs, but have electrical activity. The discharges generated by them extend to 10 ... 15 m in sea water and up to 2 m in fresh water. The main purpose of the generated electricity is location, orientation, signaling (many marine and freshwater fish: for example, horse mackerel, sable, perch, etc.).

Digestive system

In the digestive tract of real fish, the oral cavity, pharynx, esophagus, stomach, intestines (small, large, rectum ending in the anus) are distinguished. Sharks, stingrays and some other fish have a cloaca in front of the anus - an extension into which the rectum and ducts of the urinary and reproductive systems drain.

There are no salivary glands in the oral cavity of fish. The glandular cells of the oral cavity and pharynx secrete mucus, which does not have digestive enzymes and contributes only to the ingestion of food, and also protects the epithelium of the oral cavity with interspersed taste buds (receptors).

Only cyclostomes have a powerful and retractable tongue; in bony fish, it does not have its own muscles.

The mouth is usually equipped with teeth. By the presence of an enamel cap and layers of dentin, they resemble the teeth of higher vertebrates. In predators, they are located both on the jaws and on other bones of the oral cavity, sometimes even on the tongue; they are sharp. often hook-shaped, tilted inward towards the pharynx and serve to grasp and hold the prey. Many peaceful fish (many herring, cyprinids, etc.) have no teeth on their jaws.

The mechanism of nutrition is coordinated with the respiratory mechanism. Water sucked into the mouth during inhalation also carries small planktonic organisms, which, when water is pushed out of the gill cavity (exhalation), are retained in it by gill rakers.

Rice. 1 Gill rakers of planktivorous (a), benthivorous (b), predatory (c) fish.

They are so thin, long and numerous in fish that feed on plankton (plankton feeders) that they form a filtering apparatus. The filtered lump of food is sent to the esophagus. Predatory fish do not need to filter food, their stamens are rare, low, coarse, sharp or hooked: they are involved in holding the prey.

Some benthic fish have wide and massive pharyngeal teeth on the posterior branchial arch. They serve to grind food.

The esophagus following the pharynx, usually short, wide and straight with strong muscular walls, carries food to the stomach. In the walls of the esophagus there are numerous cells that secrete mucus. In open bladder fish, the duct of the swim bladder opens into the esophagus.

Not all fish have a stomach. The stomachless include cyprinids, many gobies and some others.

In the mucous membrane of the stomach there are glandular cells. producing hydrochloric acid and pepsin, which breaks down protein in an acidic environment, and mucus. This is where predatory fish digest most of their food.

The bile duct and the pancreatic duct empty into the initial part of the intestine (small intestine). Bile and pancreatic enzymes enter the intestine through them, under the action of which proteins are broken down into amino acids, fats into glycerol and fatty acids and polysaccharides are broken down into sugars, mainly glucose.

In the intestine, in addition to the breakdown of nutrients, their absorption occurs, most intensively occurring in the posterior region. This is facilitated by the folded structure of its walls, the presence of villi-like outgrowths in them, penetrated by capillaries and lymphatic vessels, the presence of cells that secrete mucus.

In many species, blind processes are placed in the initial part of the intestine - pyloric appendages, the number of which varies greatly: from 3 in perch to 400 in salmon

Cyprinids, catfish, pikes and some other fish do not have pyloric appendages. With the help of pyloric appendages, the absorptive surface of the intestine increases several times.

In fish that do not have a stomach, the intestinal tract is mostly an undifferentiated tube, tapering towards the end. In some fish, in particular carp, the anterior part of the intestine is expanded and resembles the shape of the stomach. However, this is only an external analogy: there are no pepsin-producing glands characteristic of the stomach.

The structure, shape and length of the digestive tract are diverse due to the nature of the food (food objects, their digestibility), digestion characteristics. There is a certain dependence of the length of the digestive tract on the type of food. So, the relative length of the intestine (the ratio of the length of the intestine to the length of the body.) Is in herbivores (pinagor and silver carp) - b ... 15, in omnivores (crucian carp and carp) - 2 ... 3, in carnivores (pike, pike perch, perch) - 0.6 ... 1.2.

The liver is a large digestive gland, second in size in adult fish only to the gonads. Its mass is 14 ... 25% in sharks, 1 ... 8% in bony sharks. This is a complex tubular-mesh gland, originally associated with the intestines. In embryos, it is its blind outgrowth.

The bile ducts conduct bile to the gallbladder (only a few species do not have it). Bile due to the alkaline reaction neutralizes the acid reaction of gastric juice. It emulsifies fats, activates lipase - an enzyme of the pancreas.

From the digestive tract, all blood slowly flows through the liver. In the liver cells, in addition to the formation of bile, the neutralization of foreign proteins and poisons with food occurs, glycogen is deposited, and in sharks and cod (cod, burbot, etc.). fat and vitamins. After passing through the liver, the blood travels through the hepatic vein to the heart.

The barrier function of the liver (cleansing the blood of harmful substances) determines its most important role not only in digestion, but also in blood circulation.

The pancreas, a complex alveolar gland, also a derivative of the intestine, is a compact organ only in sharks and a few other fish. In most fish, it is not visually detected, since it is diffusely embedded in the liver tissue (for the most part), and therefore it can only be distinguished on histological preparations. Each lobule is connected to an artery, a vein, a nerve ending, and a duct that leads to the gallbladder. Both glands are collectively called hepatopancreas.

The pancreas produces digestive enzymes that act on proteins, fats and carbohydrates (trypsin, erepsin, enterocokinase, lipase, amylase, maltase), which are excreted into the intestine.

In bony fish (for the first time among vertebrates), there are islets of Langerhans in the pancreatic parenchyma, in which there are numerous cells that synthesize insulin, which is secreted directly into the blood and regulates carbohydrate metabolism.

Thus, the pancreas is a gland of external and internal secretion.

From the sac-like protrusion of the dorsal part of the beginning of the intestine, a swim bladder is formed in fish - an organ peculiar only to fish.

RESPIRATORY SYSTEM AND GAS EXCHANGE

The evolution of fish led to the appearance of the gill apparatus, an increase in the respiratory surface of the gills, and a deviation from the main line of development - to the development of adaptations for using air oxygen. Most fish breathe oxygen dissolved in water, but there are species that have partially adapted to air breathing (lungfish, jumper, snakehead, etc.).

The main organs of respiration. The gills are the main organ for extracting oxygen from the water.

The shape of the gills is varied and depends on the species and mobility: pouches with folds (in fish-like), plates, petals, mucosal bundles with a rich network of capillaries. All these devices are aimed at creating the largest surface with the smallest volume.

In bony fish, the gill apparatus consists of five gill arches located in the gill cavity and covered by the gill cover. The four arches on the outer convex side each have two rows of gill filaments supported by supporting cartilages. Gill petals are covered with thin folds - petals. They are where gas exchange takes place. The number of petals varies; per 1 mm of the gill lobe they account for:

in pike - 15, flounder - 28, perch - 36. As a result, the useful respiratory surface of the gills is very large. The afferent branchial artery approaches the base of the gill filaments, its capillaries pierce the petals; of these, oxidized (arterial) blood enters the aortic root through the efferent branchial artery. In capillaries, blood flows in the opposite direction to the flow of water.

Fig. 1 Scheme of the counterflow of blood and water in the gills of fish:

1 - cartilage rod; 2 - gill arch; 3 - gill petals; 4 - gill plates; 5 - afferent artery from the abdominal aorta; 6 - efferent artery to the dorsal aorta.

More active fish have a larger gill surface: in perch it is almost 2.5 times larger than in flounder. The counterflow of blood in the capillaries and the water washing the gills ensures complete saturation of the blood with oxygen. When inhaling, the mouth opens, the gill arches move to the sides, the gill covers are pressed tightly against the head by external pressure and close the gill slits. Due to the decrease in pressure, water is sucked into the gill cavity, washing the gill filaments. When exhaling, the mouth closes, the gill arches and gill covers approach each other, the pressure in the gill cavity increases, the gill slits open and water is pushed out through them.

Rice. 2 Breathing mechanism of adult fish

When a fish swims, a current of water can be created by moving with its mouth open. Thus, the gills are located, as it were, between two pumps - oral (associated with the oral muscles) and gill (associated with the movement of the gill cover), the work of which creates pumping of water and ventilation of the gills. During the day, at least 1 m 3 of water per 1 kg of body weight is pumped through the gills.

In the capillaries of the gill filaments, oxygen is absorbed from the water (it binds to hemoglobin in the blood) and carbon dioxide, ammonia, and urea are released.

Gills also play an important role in water-salt metabolism, regulating the absorption or release of water and salts. The gill apparatus sensitively reacts to the composition of water: such toxicants as ammonia, nitrites, CO2, at an increased content, affect the respiratory folds in the very first 4 hours of contact.

Remarkable adaptations for breathing in fish in the embryonic period of development - in embryos and larvae, when the gill apparatus is not yet formed, and the circulatory system is already functioning. At this time, the respiratory organs are:

a) the surface of the body and the system of blood vessels - the Cuvier ducts, the veins of the dorsal and caudal fins, the subintestinal vein, the network of capillaries on the yolk sac, the head, the fin border and the gill cover; b) external gills

Rice. 3 Respiratory organs in fish embryos

a - pelagic fish; b - carp; in - loach; 1 - Cuvier ducts; 2 - lower tail vein; 3 - network of capillaries; 4 - external gills.

These are temporary, specific larval formations that disappear after the formation of the definitive respiratory organs. The worse the breathing conditions of embryos and larvae, the stronger the development of the circulatory system or external gills. Therefore, in fish that are systematically close but differ in their spawning ecology, the degree of development of the larval respiratory organs is different.

Additional organs of respiration. Additional devices that help to endure adverse oxygen conditions include water skin respiration, i.e. the use of oxygen dissolved in water with the help of the skin, and air respiration - the use of air with the help of a swim bladder, intestines or through special additional organs

Breathing through the skin of the body is one of the characteristic features of aquatic animals. And although in fish scales make it difficult to breathe with the surface of the body, in many species the role of the so-called skin respiration is great, especially in adverse conditions. According to the intensity of such breathing, freshwater fish are divided into three groups:

1. Fish adapted to live in conditions of severe oxygen deficiency. These are fish that inhabit well-warmed water bodies with a high content of organic substances, in which there is often a lack of oxygen. In these fish, the share of skin respiration in total respiration is 17 ... 22%, in some individuals - 42 ... 80%. These are carp, crucian carp, catfish, eel, loach. At the same time, fish, in which the skin is of the greatest importance in respiration, are devoid of scales or it is small and does not form a continuous cover. For example, in a loach, 63% of oxygen is absorbed by the skin, 37% by the gills; when the gills are turned off, up to 85% of oxygen is consumed through the skin, and the rest enters through the intestines.

2. Fish less oxygen deficient and exposed to adverse conditions less frequently. These include living at the bottom, but in running water, sturgeons - sterlet, sturgeon, stellate sturgeon. The intensity of their skin respiration is 9 ... 12%.

3. Fish that do not fall into conditions of oxygen deficiency, living in flowing or stagnant, but clean, oxygen-rich waters. The intensity of skin respiration does not exceed 3.3 ... 9%. These are whitefish, smelt, perch, ruff.

Carbon dioxide is also released through the skin. So, in the loach, up to 92% of the total amount is excreted in this way.

In the extraction of oxygen from the air in a humid atmosphere, not only the surface of the body, but also the gills are involved. Temperature plays an important role in this.

Crucian carp (11 days), tench (7 days), carp (2 days) differ in the highest survival in a humid environment, while bream, rudd, bleak can live without water for only a few hours, and then at low temperatures.

When transporting live fish without water, skin respiration almost completely provides the body's need for oxygen.

Some fish living in adverse conditions have developed adaptations for breathing oxygen from the air. For example, breathing with the help of the intestines. Clusters of capillaries form in the walls of the intestine. The air swallowed by the mouth passes through the intestines, and in these places the blood absorbs oxygen and releases carbon dioxide, while up to 50% of oxygen is absorbed from the air. This type of breathing is characteristic of loach, some catfish and carp fish; its value in different fish is not the same. For example, in loaches under conditions of a large lack of oxygen, it is this method of breathing that becomes almost equal to the gill.

When fish die, they swallow air with their mouths; air aerates the water in the mouth, which then passes through the gills.

Another way of using atmospheric air is the formation of special additional organs: for example, the labyrinth in labyrinth fish, the supragill in the snakehead, etc.

Labyrinth fish have a labyrinth - an expanded pocket-like section of the gill cavity, the folded walls of which are penetrated by a dense network of capillaries in which gas exchange occurs. In this way, the fish breathe the oxygen of the atmosphere and can stay out of the water for several days (the tropical creeper perch Anabas sp. comes out of the water and climbs rocks and trees).

Tropical mudskippers (Periophthalmus sp.) have gills surrounded by sponge-like tissue soaked in water. When these fish land on land, the gill covers close tightly and protect the gills from drying out. In the snakehead, the protrusion of the pharynx forms the supragillary cavity, the mucous membrane of its walls is equipped with a dense network of capillaries. Due to the presence of the supragillary organ, it breathes air and can be in shallow water at 30 ° C. For normal life, a snakehead, like a crawler, needs both oxygen dissolved in water and atmospheric oxygen. However, during wintering in ponds covered with ice, he does not use atmospheric air.

The swim bladder is also designed to use the oxygen in the air. It reaches its greatest development as a respiratory organ in lungfish. They have it cellular and functions like a lung. This creates a “pulmonary circle” of blood circulation,

The composition of gases in the swim bladder is determined both by their content in the reservoir and by the condition of the fish.

Mobile and predatory fish have a large supply of oxygen in the swim bladder, which is consumed by the body during prey throws, when the supply of oxygen through the respiratory organs is insufficient. In unfavorable oxygen conditions, the air of the swim bladder in many fish is used for breathing. Loach and eel can live out of water for several days, provided that the moisture of the skin and gills is maintained: if in water the gills provide the eel with 85 ... 90% of the total oxygen absorption, then in the air it is only a third. Out of the water, the eel uses the oxygen in the swim bladder and the air passing through the skin and gills for breathing. This allows him to even crawl from one body of water to another. Carp and carp, which do not have any special devices for using atmospheric air, partially absorb oxygen from the swim bladder when out of water.

Mastering various reservoirs, fish have adapted to life under different gas regimes. The most demanding on the oxygen content in the water are salmon, which need an oxygen concentration of 4.4 ... 7 mg / l for normal life; grayling, chub, burbot feel good at a content of at least 3.1 mg/l; 1.9 ... 2.5 mg / l is usually sufficient for cyprinids.

Each species has its own oxygen threshold, that is, the minimum oxygen concentration at which the fish dies. Trout begins to suffocate at an oxygen concentration of 1.9 mg / l, pike perch and bream die at 1.2, roach and rudd - at 0.25 ... 0.3 mg / l; in carps of the year grown on natural food, the oxygen threshold was noted at 0.07 ... 0.25 mg / l, and for two-year-olds - 0.01 ... 0.03 mg / l of oxygen. Carp and rotan - partial anaerobes - can live for several days without oxygen at all, but at low temperatures. It is assumed that the body first uses oxygen from the swim bladder, then liver and muscle glycogen. Apparently, fish have special receptors in the anterior part of the dorsal aorta or in the medulla oblongata, which perceive a drop in the oxygen concentration in the blood plasma. The endurance of fish is promoted by a large amount of carotenoids in the nerve cells of the brain, which are able to accumulate oxygen and give it away when there is a shortage.

The intensity of respiration depends on biotic and abiotic factors. Within one species, it varies depending on size, age, mobility, feeding activity, sex, degree of gonadal maturity, and physicochemical environmental factors. As the fish grows, the activity of oxidative processes in the tissues decreases; maturation of the gonads, on the contrary, causes an increase in oxygen consumption. The oxygen consumption in the body of males is higher than that of females.

In addition to the concentration of oxygen in water, the rhythm of respiration is influenced by the content of CO2, pH, temperature, etc. For example, at a temperature of 10 ° C and an oxygen content of 4.7 mg / l, trout makes 60 ... 2 kg / l respiratory rate increases to 140 ... 160; carp at 10 ° C breathes almost twice as slowly as trout (30 ... 40 times per minute), in winter it makes 3 ... 4 and even 1 ... 2 respiratory movements per minute.

Like a sharp lack of oxygen, excessive saturation of water with it has a detrimental effect on fish. Thus, the lethal limit for pike embryos is 400% saturation of water with oxygen, at 350 .. .430% saturation, the motor activity of roach embryos is disturbed. Sturgeon growth decreases at 430% saturation.

Incubation of eggs in water supersaturated with oxygen leads to a slowdown in the development of embryos, a strong increase in waste and the number of freaks, and even death. In fish, gas bubbles appear on the gills, under the skin, in blood vessels, organs, and then convulsions and death occur. This is called gas embolism or gas bubble disease. However, death does not occur due to excess oxygen, but due to a large amount of nitrogen. For example, in salmon larvae and fry die at 103 ... 104%, underyearlings - 105 ... 113, adult fish - at 118% water saturation with nitrogen.

To maintain the optimal concentration of oxygen in the water, which ensures the most efficient course of physiological processes in the body of fish, it is necessary to use aeration installations.

To a small supersaturation of oxygen, fish adapt quickly. Their metabolism increases and as a result, feed intake increases and the feed coefficient decreases, embryo development accelerates, and waste is reduced.

For the normal breathing of fish, the content of CO2 in the water is very important. With a large amount of carbon dioxide, fish breathing is difficult, since the ability of blood hemoglobin to bind oxygen decreases, blood oxygen saturation sharply decreases and the fish suffocates. When the content of CO2 in the atmosphere is 1...5% CO2; blood cannot flow out, and blood cannot take in oxygen even from oxygenated water.

Circulatory system

The main difference between the circulatory system of fish and other vertebrates is the presence of one circle of blood circulation and a two-chambered heart filled with venous blood (with the exception of lungfish and crossopterans).

The heart consists of one ventricle and one atrium and is placed in the pericardial sac, immediately behind the head, behind the last branchial arches, that is, it is shifted forward compared to other vertebrates. In front of the atrium there is a venous sinus, or venous sinus, with falling walls; Through this sinus, blood enters the atrium, and from it into the ventricle.

The enlarged initial section of the abdominal aorta in lower fish (sharks, rays, lungfish) forms a contracting arterial cone, and in higher fish it forms an aortic bulb, the walls of which cannot contract. The backflow of blood is prevented by valves.

The circulatory scheme in its most general form is presented as follows. Venous blood filling the heart, with contractions of a strong muscular ventricle, through the arterial bulb along the abdominal aorta, is sent forward and rises to the gills along the afferent branchial arteries. In bony fish, there are four on each side of the head, according to the number of gill arches. In the gill filaments, blood passes through the capillaries and oxidized, oxygenated blood is sent through the efferent vessels (there are also four pairs) to the roots of the dorsal aorta, which then merge into the dorsal aorta, which runs along the body back, under the spine. The connection of the roots of the aorta in front forms the head circle characteristic of bony fish. The carotid arteries branch off anteriorly from the roots of the aorta.

Arteries run from the dorsal aorta to the internal organs and muscles. In the caudal region, the aorta passes into the caudal artery. In all organs and tissues, arteries break up into capillaries. The venous capillaries that collect venous blood flow into a vein that carries blood to the heart. The tail vein, which begins in the caudal region, enters the body cavity and divides into the portal veins of the kidneys. In the kidneys, the ramifications of the portal veins form the portal system, and after exiting them, they merge into the paired posterior cardinal veins. As a result of the confluence of the posterior cardinal veins with the anterior cardinal (jugular) veins, which collect blood from the head, and the subclavian, which bring blood from the pectoral fins, two Cuvier ducts are formed, through which blood enters the venous sinus. Blood from the digestive tract (stomach, intestines) and spleen, passing through several veins, is collected in the portal vein of the liver, the branches of which in the liver form the portal system. The hepatic vein that collects blood from the liver flows directly into the venous sinus

Rice. 1 Scheme of the circulatory system of bony fish:

1 - venous sinus; 2 - atrium; 3 - ventricle; 4 - aortic bulb; 5 - abdominal aorta; 6 - afferent branchial arteries; efferent branchial arteries; 8 - roots of the dorsal aorta; 9 - anterior jumper connecting the roots of the aorta; 10 - carotid artery; 11 - dorsal aorta; 12 - subclavian artery; 13 - intestinal artery; 14 - mesenteric artery; 15 - tail artery; 16 - tail vein; 17 - portal veins of the kidneys; 18 - posterior cardinal vein; 19 - anterior cardinal vein; 20 - subclavian vein; 21 - Cuvier duct; 22 - portal vein of the liver; 23 - liver; 24 - hepatic vein; black shows vessels with venous blood, white with arterial blood.

Like other vertebrates, cyclostomes and fish have so-called additional hearts that maintain pressure in the vessels. So, in the dorsal aorta of the rainbow trout there is an elastic ligament that acts as a pressure pump, which automatically increases blood circulation during swimming, especially in the muscles of the body. The intensity of the additional heart depends on the frequency of movements of the caudal fin.

Lungfish have an incomplete atrial septum. This is accompanied by the emergence of the pulmonary circulation, passing through the swim bladder, turned into a lung.

The heart of fish is much smaller and weaker than that of terrestrial vertebrates. Its mass usually does not exceed 2.5%, on average 1% of body weight, while in mammals it reaches 4.6%, and in birds even 16%.

Blood pressure (Pa) in fish is low - 2133.1 (stingray), 11198.8 (pike), 15998.4 (salmon), while in the carotid artery of the horse - 20664.6.

The frequency of contractions of the heart is also low - 18 ... 30 beats per minute, and it strongly depends on temperature: at low temperatures in fish wintering in pits, it decreases to 1 ... 2; in fish that tolerate freezing into ice, the heart pulsation stops for this period.

The amount of blood in fish is less than in all other vertebrates (1.1,..7.3% of body weight, including carp 2.0 ... 4.7%, catfish - up to 5, pike - 2 , chum salmon - 1.6, while in mammals - 6.8% on average). This is due to the horizontal position of the body (there is no need to push the blood up) and less energy expenditure due to life in the aquatic environment. Water is a hypogravitational medium, i.e., the force of gravity here has almost no effect.

The morphological and biochemical characteristics of blood are different in different species due to the systematic position, characteristics of the habitat and lifestyle. Within one species, these indicators fluctuate depending on the season of the year, conditions of detention, age, sex, and condition of individuals. Fish erythrocytes are larger, and their number in the blood is less than in higher vertebrates, while leukocytes, as a rule, are more. This is connected, on the one hand, with a reduced metabolism of fish, and on the other hand, with the need to strengthen the protective functions of the blood, since the environment is replete with pathogens. In 1 mm 3 of blood, the number of erythrocytes is (million): in primates, 9.27; ungulates - 11.36; cetaceans - 5.43; birds - 1.61 ... 3.02; bony fish - 1.71 (freshwater), 2.26 (marine), 1.49 (anadromous).

The number of erythrocytes in fish varies widely, primarily depending on their mobility: in carp - 0.84 ... 1.89 million / mm 3 of blood, pike - 2.08, bonito - 4.12 million / mm 3. The number of leukocytes in carp is 20 ... 80, in ruff - 178 thousand / mm 3. Fish leukocytes are very diverse. In most species, there are both granular (neutrophils, eosinophils) and non-granular (lymphocytes, monocytes) forms of leukocytes in the blood. Lymphocytes predominate, accounting for 80...95%, monocytes account for 0.5...11%, neutrophils—13...31%. Eosinophils are rare. For example, cyprinids, Amur herbivores and some perch fish have them.

The ratio of different forms of leukocytes in the blood of carp depends on the age and growing conditions.

The number of leukocytes varies greatly during the year:

in carp, it rises in summer and decreases in winter during starvation due to a decrease in the intensity of metabolism.

A variety of shapes, sizes and quantities is also characteristic of platelets involved in blood clotting.

The blood of fish is colored red by hemoglobin, but there are fish with colorless blood. In such fish, oxygen in the dissolved state is carried by the plasma. Thus, representatives of the family Chaenichthyidae (from the suborder Nototheniidae) living in the Antarctic seas at low temperatures (

The amount of hemoglobin in the body of fish is much less than that of terrestrial vertebrates: they have 0.5 ... 4 g per 1 kg of body, while in mammals it is 5 ... 25 g. Fish that move quickly have more hemoglobin than in sedentary ones: in migratory sturgeon 4 g/kg, in burbot 0.5 g/kg. The amount of hemoglobin depends on the season (in carp it increases in winter and decreases in summer), the hydrochemical regime of the reservoir (in water with a pH of 5.2, the amount of hemoglobin in the blood increases), nutritional conditions (carps grown on natural food and additional feed have different amounts of hemoglobin ). The growth rate of fish depends on the amount of hemoglobin.

Living in an environment with a low oxygen content determined a low metabolic rate and a higher saturation capacity at a lower partial pressure of oxygen, in contrast to air-breathing vertebrates. The ability of hemoglobin to extract oxygen from water varies from fish to fish. Fast-swimming (mackerel, cod, trout) have a lot of hemoglobin in the blood, and they are very demanding on the oxygen content in the water. In many marine bottom fish, as well as eel, carp, crucian carp and some others, on the contrary, there is little hemoglobin in the blood, but it can take oxygen from the environment even with a small amount.

For example, for zander to saturate the blood with oxygen (at 16 ° C), the content in water is 2.1 ... 2.3 O2 mg / l; in the presence of 0.56 ... 0.6 O2 mg / l in the water, the blood begins to give it away, breathing becomes impossible, and the fish dies. I bream at the same temperature to completely saturate hemoglobin with oxygen, the presence of 1.0 ... 1.06 mg of oxygen in a liter of water is sufficient.

The sensitivity of fish to changes in water temperature is also associated with the properties of hemoglobin: as the temperature rises, the body's need for oxygen increases, but the ability of hemoglobin to take it decreases.

It reduces the ability of hemoglobin to take in oxygen and carbon dioxide: in order for the blood saturation of an eel with oxygen to reach 50% with a content of 1% CO2 in water, an oxygen pressure of 666.6 Pa is necessary, and in the absence of CO2, an oxygen pressure of almost half as much is sufficient for this - 266, 6. „399.9 Pa,

Blood groups in fish were first identified on the Baikal omul and grayling in the 30s of this century. To date, it has been established that the group antigenic differentiation of erythrocytes is widespread: 14 systems of blood groups have been identified, including more than 40 erythrocyte antigens. With the help of immunoserological methods, variability is studied at different levels: differences between species and subspecies and even between intraspecific groups in salmon (when studying the relationship of trout), sturgeons (when comparing local stocks) and other fish were revealed.

Blood, being the internal environment of the body, performs the most important functions: it carries proteins, carbohydrates (glycogen, glucose, etc.) and other nutrients that play an important role in energy and plastic metabolism; respiratory—transportation of oxygen to the tissues and carbon dioxide to the respiratory organs; excretory - the removal of end products of metabolism to the organs of excretion; regulatory - the transfer of hormones and other active substances from the endocrine glands to organs and tissues; protective - the blood contains antimicrobial substances (lysozyme, complement, interferon, properdin), antibodies are formed, the leukocytes circulating in it have a phagocytic ability. The level of these substances in the blood depends on the biological characteristics of fish and abiotic factors, and the mobility of the blood composition makes it possible to use its indicators to assess the physiological state.

The bone marrow, which is the main organ for the formation of blood cells in higher vertebrates, and fish do not have lymph glands (nodes).

Hematopoiesis in fish, compared with higher vertebrates, differs in a number of features.

1. The formation of blood cells occurs in many organs. The foci of hematopoiesis are: gill apparatus (vascular endothelium and reticular syncytium, concentrated at the base of the gill filaments), intestines (mucosa), heart (epithelial layer and vascular endothelium), kidneys (reticular syncytium between tubules), spleen, vascular blood, lymphoid organ ( accumulations of hematopoietic tissue - reticular syncytium - under the roof of the skull). On the imprints of these organs, blood cells of different stages of development are visible.

2. In bony fish, hematopoiesis most actively occurs in the lymphoid organs, kidney and spleen, and the main hematopoietic organ is the kidneys, namely their anterior part. In the kidneys and spleen, both the formation of erythrocytes, leukocytes, platelets and the breakdown of erythrocytes occur.

3. The presence of mature and young erythrocytes in the peripheral blood of fish is normal and does not serve as a pathological indicator, unlike the blood of adult mammals.

4. Erythrocytes have a nucleus, like other aquatic animals, as a result of which their viability is longer than that of mammals.

The spleen of fish is located in the anterior part of the body cavity, between the intestinal loops, but independently of it. This is a dense compact dark red formation of various shapes (spherical, ribbon-like), but more often elongated.

The spleen quickly changes volume under the influence of external conditions and the condition of the fish. In carp, it increases in winter, when, due to a reduced metabolism, the blood flow slows down and it accumulates in the spleen, liver and kidneys, which serve as a blood depot, the same is observed in acute diseases. With a lack of oxygen, water pollution, transportation and sorting of fish, fishing of ponds, reserves from the spleen enter the bloodstream.

One of the most important factors of the internal environment is the osmotic pressure of the blood, since the interaction of blood and body cells, water exchange in the body depends on it.

The circulatory system is subject to nervous (vagus nerve) and humoral (hormones, Ca, K ions) regulation. The central nervous system of fish receives information about the work of the heart from the baroreceptors of the gill vessels.

The lymphatic system of fish does not have glands. It is represented by a number of paired and unpaired lymphatic trunks, into which lymph is collected from organs and is also discharged through them to the terminal sections of the veins, in particular to the Cuvier ducts. Some fish have lymphatic hearts.

NERVOUS SYSTEM AND SENSORS

Nervous system. In fish, it is represented by the central nervous system and the peripheral and autonomic (sympathetic) nervous systems associated with it.
The central nervous system consists of the brain and spinal cord. The peripheral nervous system includes nerves that extend from the brain and spinal cord to the organs. The autonomic nervous system basically has numerous ganglia and nerves innervating the muscles of the internal organs and blood vessels of the heart.
The nervous system of fish, in comparison with the nervous system of higher vertebrates, is characterized by a number of primitive features.
The central nervous system has the form of a neural tube stretching along the body: part of it, lying above the spine and protected by the upper arches of the vertebrae, forms the spinal cord, and the expanded anterior part, surrounded by a cartilaginous or bone skull, makes up the brain.

Rice. 1 fish brain (perch):

1- olfactory capsules; 2- olfactory lobes; 3- forebrain; 4- midbrain; 5- cerebellum; 6- medulla oblongata; 7- spinal cord; 8,9,10 - head nerves.

The cavities of the anterior, diencephalon, and medulla oblongata are called ventricles: the cavity of the midbrain is called the Sylvian aqueduct (it connects the cavities of the diencephalon and medulla oblongata, i.e., the third and fourth ventricles).
The forebrain, due to the longitudinal groove, has the appearance of two hemispheres. The olfactory bulbs (primary olfactory center) are adjacent to them either directly (in most species), or through the olfactory tract (cyprinids, catfish, cod).
There are no nerve cells in the roof of the forebrain. Gray matter in the form of striatal bodies is concentrated mainly in the base and olfactory lobes, lines the cavity of the ventricles and makes up the main mass of the forebrain. The fibers of the olfactory nerve connect the bulb with. olfactory capsule cells.
The forebrain is the center for processing information from the olfactory organs. Due to its connection with the diencephalon and midbrain, it is involved in the regulation of movement and behavior. In particular, the forebrain takes part in the formation of the ability for such acts as spawning, spawn guarding, flock formation, aggression, etc.
Visual tubercles are developed in the diencephalon. The optic nerves depart from them, forming a chiasm (crossover, i.e., part of the fibers of the right nerve passes into the left nerve and vice versa). On the underside of the diencephalon, or hypothalamus, there is a funnel to which the pituitary gland, or pituitary gland, adjoins; in the upper part of the diencephalon, the epiphysis, or pineal gland, develops. The pituitary and pineal glands are endocrine glands.
The diencephalon performs numerous functions. It perceives irritations from the retina of the eye, participates in the coordination of movements, processing information from other sense organs. The pituitary and pineal glands carry out hormonal regulation of metabolic processes.
The midbrain is the largest in size. It has the appearance of two hemispheres, which are called visual lobes. These lobes are the primary visual centers that perceive excitation. From them, the fibers of the optic nerve originate.
In the midbrain, signals from the organs of vision and balance are processed; here are the centers of communication with the cerebellum, medulla oblongata and spinal cord, regulation of color, taste.
The cerebellum is located in the back of the brain and can take the form of either a small tubercle adjacent to the back of the midbrain, or a large saccular-elongated formation adjacent to the top of the medulla oblongata. The cerebellum in catfish reaches a particularly large development, and in Mormirus it is the largest among all vertebrates. The cerebellum of fish contains Purkinje cells.
The cerebellum is the center of all motor innervations in swimming and grasping food. It "provides coordination of movements, maintaining balance, muscle activity, is associated with the receptors of the lateral line organs, directs and coordinates the activity of other parts of the brain. If the cerebellum is damaged, for example, in carp and silver carp, muscle atony occurs, balance is disturbed, they are not produced or disappear conditioned reflexes to light and sound.
The fifth part of the brain - the medulla oblongata without a sharp border passes into the spinal cord. The cavity of the medulla oblongata - the fourth ventricle continues into the cavity
spinal cord - neurocoel. A significant mass of the medulla oblongata consists of white matter.
Most (six out of ten) of the cranial nerves depart from the medulla oblongata. It is the center of regulation of the activity of the spinal cord and the autonomic nervous system. It contains the most important vital centers that regulate the activity of the respiratory, musculoskeletal, circulatory, digestive, excretory systems, organs of hearing and balance, taste, lateral line and electrical organs. Therefore, when the medulla oblongata is destroyed, for example, when the body is cut behind the head, a quick death of the fish occurs.
Through the spinal fibers coming to the medulla oblongata, the connection between the medulla oblongata and the spinal cord is carried out.
10 pairs of cranial nerves depart from the brain: 1 - olfactory nerve (nervus olfactorius) from the sensory epithelium of the olfactory capsule brings irritation to the olfactory bulbs of the forebrain; 2-optic nerve (n. opticus) stretches to the retina from the visual tubercles of the diencephalon; 3-oculomotor nerve (n. oculo-motorius) innervates the muscles of the eye, moving away from the midbrain;
4 - trochlear nerve (n. trochlearis) - oculomotor, stretching from the midbrain to one of the muscles of the eye; 5-trigeminal nerve (n. trigeminus), extending from the lateral surface of the medulla oblongata and giving three main branches-orbital, maxillary and mandibular; 6 - abducens nerve (n. abducens) stretches from the bottom of the brain to the rectus muscle of the eye; 7-facial nerve (n. facialis) departs from the medulla oblongata and gives numerous branches to the muscles of the hyoid arch, oral mucosa, scalp (including the lateral line of the head); 8-auditory nerve (n. acusticus) connects the medulla oblongata and the auditory apparatus; 9-glossopharyngeal nerve (n. glossopharingeus) goes from the medulla oblongata to the pharynx, innervates the mucous membrane of the pharynx and the muscles of the first gill arch; 10-vagus nerve (n. vagus) - the longest, connects the medulla oblongata with gill apparatus, intestinal tract, heart, swim bladder, lateral line.
The degree of development of different parts of the brain is different in different groups of fish and is associated with lifestyle.
The forebrain and olfactory lobes are better developed in cartilaginous fish (sharks and rays) and worse in teleosts. In sedentary fish, such as bottom fish (flounder), the cerebellum is small, but the anterior and medulla oblongata are more developed in accordance with the important role of smell and touch in their life. In well-swimming fish (pelagic, plankton-feeding, and predatory), the midbrain (visual lobes) and cerebellum (due to the need for rapid movement coordination) are more developed. Fish that live in muddy waters have small visual lobes and a small cerebellum. The visual lobes are poorly developed in deep-sea fish. The electrical activity of different parts of the brain is also different: in silver carp, electrical waves in the cerebellum go at a frequency of 25 ... 35 times per second, in the forebrain - 4 ... 8.
The spinal cord is a continuation of the medulla oblongata. It has the shape of a rounded cord and lies in the canal formed by the upper arches of the vertebrae. Unlike higher vertebrates, it is capable of regeneration and restoration of activity. In the spinal cord, gray matter is on the inside and white matter is on the outside.
The function of the spinal cord is reflex and conductive. It contains the centers of vasomotor, trunk muscles, chromatophores, electrical organs. From the spinal cord metamerically, i.e., corresponding to each vertebra, the spinal nerves depart, innervating the surface of the body, the trunk muscles, and, thanks to the connection of the spinal nerves with the ganglia of the sympathetic nervous system, the internal organs. In the spinal cord of bony fish there is a secretory organ - the urohypophysis, whose cells produce a hormone involved in water metabolism.
The autonomic nervous system in cartilaginous fish is represented by disjointed ganglia lying along the spine. Ganglion cells with their processes are in contact with the spinal nerves and internal organs.
In bony fish, the ganglia of the autonomic nervous system are connected by two longitudinal nerve trunks. The connecting branches of the ganglia connect the autonomic nervous system with the central one. The interrelationships of the central and autonomic nervous systems create the possibility of some interchangeability of nerve centers.
The autonomic nervous system acts independently of the central nervous system and determines the involuntary automatic activity of the internal organs, even if its connection with the central nervous system is broken.
The reaction of the fish organism to external and internal stimuli is determined by the reflex. Fish can develop a conditioned reflex to light, shape, smell, taste, sound, water temperature and salinity. So, aquarium and pond fish soon after the start of regular feeding accumulate at a certain time at the feeders. They also get used to sounds during feeding (tapping on the walls of the aquarium, ringing a bell, whistling, blows) and for some time swim up to these stimuli even in the absence of food. At the same time, reflexes to receive food are formed in fish faster, and disappear more slowly than in chickens, rabbits, dogs, and monkeys. In crucian carp, the reflex appears after 8 combinations of a conditioned stimulus with an unconditioned one, and fades after 28 ... 78 unreinforced signals.
Behavioral reactions are developed faster in fish in a group (imitation, following the leader in a flock, reaction to a predator, etc.). Temporary memory and training is of great importance in fish breeding practice. If fish are not taught defensive reactions, communication skills with predators, then juveniles released from fish hatcheries quickly die in natural conditions.
The organs of perception of the environment (sense organs) of fish have a number of features that reflect their adaptability to living conditions. The ability of fish to perceive information from the environment is diverse. Their receptors can detect various stimuli of both physical and chemical nature: pressure, sound, color, temperature, electric and magnetic fields, smell, taste. Some stimuli are perceived as a result of direct touch (touch, taste), others at a distance.
Organs that perceive chemical, tactile (touch), electromagnetic, temperature and other stimuli have a simple structure. Irritations are caught by the free nerve endings of the sensory nerves on the surface of the skin. In some groups of fish, they are represented by special organs or are part of the lateral line.
In connection with the peculiarities of the living environment in fish, chemical sense systems are of great importance. Chemical stimuli are perceived using the sense of smell (sensation of smell) or non-olfactory reception organs, which provide the perception of taste, changes in the activity of the environment, etc.
The chemical sense is called chemoreception, and the sensory organs are called chemoreceptors. Chemoreception helps fish find and evaluate food, individuals of their own species and of the opposite sex, avoid enemies, navigate in a stream, and defend territory.
Organs of smell. In fish, like other vertebrates, they are located in the anterior part of the head and are represented by paired olfactory (nasal) sacs (capsules) that open outward through openings—nostrils. The bottom of the nasal capsule is lined with folds of epithelium, consisting of supporting and sensory cells (receptors). The outer surface of the sensory cell is provided with cilia, and the base is connected with the endings of the olfactory nerve. Receptor surface
organ is large: on the I square. mm. The olfactory epithelium accounts for Phoxinus 95,000 receptor cells. The olfactory epithelium contains numerous mucus-secreting cells.
The nostrils are located in cartilaginous fish on the underside of the snout in front of the mouth, in bony fish - on the dorsal side between the mouth and eyes. Cyclostomes have one nostril, real fish have two. Each nostril is divided by a leathery septum into two parts called foramens. Water penetrates into the anterior, washes the cavity and exits through the posterior opening, washing and irritating the hairs of the receptors.
Under the influence of odorous substances in the olfactory epithelium, complex processes occur: the movement of lipids, protein-mucopolysaccharide complexes and acid phosphatase. The electrical activity of the olfactory epithelium in response to different odorous substances is different.
The size of the nostrils is related to the way of life of fish: in moving fish they are small, since during fast swimming the water in the olfactory cavity is updated quickly; inactive fish have large nostrils, they pass a larger volume of water through the nasal cavity, which is especially important for poor swimmers, in particular, those living near the bottom.
Fish have a subtle sense of smell, i.e., their thresholds for olfactory sensitivity are very low. This especially applies to nocturnal and twilight fish, as well as to those living in muddy waters, for whom vision does little to help them find food and communicate with relatives.
The sense of smell is most sensitive in migratory fish. Far Eastern salmon definitely find their way from feeding grounds in the sea to spawning grounds in the upper reaches of the rivers, where they hatched several years ago. At the same time, they overcome huge distances and obstacles - currents, rapids, rifts. However, fish find their way correctly only if their nostrils are open, and if they are filled with cotton wool or vaseline, then the fish walk randomly. It is assumed that at the beginning of migration salmon are guided by the sun and stars and, approximately 800 km from their native river, accurately determine the path due to chemoreception.
In experiments, when the nasal cavity of these fish was washed off with water from their native spawning ground, a strong electrical reaction arose in the olfactory bulb of the brain. The reaction to water from downstream tributaries was weak, and the receptors did not react at all to water from foreign spawning grounds.
With the help of the cells of the olfactory bulb, sockeye salmon juveniles can distinguish between the water of different lakes, solutions of various amino acids in a dilution of Yu "4, as well as the concentration of calcium in the water. No less striking is the similar ability of the European
eel migrating from Europe to spawning grounds located in the Sargasso Sea. It is estimated that the eel is able to recognize the concentration created by diluting 1 g of phenylethyl alcohol in a ratio of 1:3-10 -18 . Fish catch the fear pheromone at a concentration of 10 -10 g / l: High selective sensitivity to histamine, as well as to carbon dioxide (0.00132 ... 0.0264 g / l) was found in carp.
The olfactory receptor of fish, in addition to chemical ones, is able to perceive both mechanical influences (flow jets) and temperature changes.
organs of taste. They are represented by taste buds, formed by clusters of sensory and supporting cells. The bases of the sensory cells are entwined with terminal branches of the facial, vagus, and glossopharyngeal nerves. The perception of chemical stimuli is also carried out by the free nerve endings of the trigeminal, vagus and spinal nerves.
The perception of taste by fish is not necessarily associated with the oral cavity, since the taste buds are located in the mucous membrane of the oral cavity, on the lips, in the pharynx, on the antennae, gill filaments, fin rays and over the entire surface of the body, including the tail.
Catfish perceives taste mainly with the help of whiskers, since taste buds are concentrated in their epidermis. The number of these kidneys increases as the body size of the fish increases.
Fish also distinguish the taste of food: bitter, salty, sour, sweet. In particular, the perception of salinity is associated with a pit-shaped organ located in the oral cavity.
The sensitivity of the taste organs in some fish is very high: for example, cave fish Anoptichtys, being blind, feel a glucose solution at a concentration of 0.005%. Fish recognize changes in salinity up to 0.3 ^ / oo, pH - 0.05 ... 0.007, carbon dioxide - 0.5 g / l, NaCl - 0.001 ... 0.005 mol (cyprinids), and minnow - even 0.00004 pray.
lateral line sense organs. A specific organ, peculiar only to fish and amphibians living in the water, is the organ of the lateral sense, or lateral line. This is a seismosensory specialized skin organ. These organs are most simply arranged in cyclostomes and larvae of cyprinids. Sensory cells (mechanoreceptors) lie among clusters of ectodermal cells on the surface of the skin or in small pits. At the base, they are braided with the terminal branches of the vagus nerve, and in the area that rises above the surface, they have cilia that perceive water vibrations. In most adult teleosts, these organs are
channels immersed in the skin, stretching along the sides of the body along the midline. The channel opens outward through holes (pores) in the scales located above it. Branchings of the lateral line are also present on the head.

Sensory cells with cilia lie in groups at the bottom of the canal. Each such group of receptor cells, together with the nerve fibers in contact with them, forms an organ proper—a neuromast. Water flows freely through the channel and the cilia feel its pressure. In this case, nerve impulses of different frequencies arise.
The lateral line organs are connected to the central nervous system by the vagus nerve.
The lateral line may be complete, i.e., stretch along the entire length of the body, or incomplete and even absent, but in the latter case, the head canals develop strongly, as, for example, in herring.
By the lateral line, the fish feels the change in the pressure of the flowing water, vibrations (oscillations) of low frequency, infrasonic vibrations and electromagnetic fields. For example, carp picks up current at a density of 60 μA/cm 2 , crucian carp—16 μA/cm 2 .
The lateral line captures the pressure of a moving stream, and it does not perceive a change in pressure when diving to a depth. Capturing fluctuations in the water column, the fish detects surface waves, currents, underwater stationary (rocks, reefs) and moving (enemies, prey) objects.
The lateral line is a very sensitive organ: the shark catches the movement of fish at a distance of 300 m, migratory fish feel even slight currents of fresh water in the sea.
The ability to capture waves reflected from living and inanimate objects is very important for deep-sea fish, since ordinary visual perception is impossible in the darkness of great depths.
It is assumed that during mating games, fish perceive the sideline of the wave as a signal from the female or male to spawn. The function of the skin sense is also performed by the so-called skin buds - cells present in the integument of the head and antennae, to which the nerve endings fit, but they are of much lesser importance.
Organs of touch. They are clusters of sensory cells (tactile bodies) scattered over the surface of the body. They perceive the touch of solid objects (tactile sensations), water pressure, temperature changes, and pain.
There are especially many sensory skin buds in the mouth and on the lips. In some fish, the function of these organs is performed by elongated rays of the fins: in gourami, this is the first ray of the ventral fin, in trigla (sea cock) touch is associated with the rays of the pectoral fins, which feel the bottom. In inhabitants of muddy waters or bottom fish, most active at night, the largest number of sensory buds are concentrated on the antennae and fins. In males, whiskers serve as taste receptors.
Mechanical injuries and pain seem to be less felt in fish than in other vertebrates. So, sharks that pounce on prey do not react to blows with a sharp object to the head.
Thermoreceptors. They are the free endings of the sensory nerves located in the surface layers of the skin, with the help of which the fish perceive the temperature of the water. There are receptors that perceive heat (thermal) and cold (cold). Points of heat perception are found, for example, in pike on the head, cold perception points are found on the surface of the body. Bony fish catch temperature drops of 0.1 ... 0.4 degrees. In trout, it is possible to develop a conditioned reflex to very small (less than 0.1 degrees) and rapid changes in temperature.
The lateral line and the brain are very sensitive to temperature. Temperature-sensitive neurons similar to neurons in mammalian thermoregulatory centers have been found in the fish brain. Trout have neurons in the diencephalon that respond to temperature rises and falls.
Organs of electrical sense. The organs of perception of electric and magnetic fields are located in the skin on the entire surface of the body of fish, but mainly in different parts of the head and around it. They are similar to the organs of the lateral line:
these are pits filled with a mucous mass that conducts electricity well; at the bottom of the pits, sensory cells (electroreceptors) are placed that transmit "nerve impulses to the brain. Sometimes they are part of the lateral line system. The ampullae of Lorenzini also serve as electrical receptors in cartilaginous fish. Analysis of the information received by the electroreceptors is carried out by the lateral line analyzer, which is located in medulla oblongata and cerebellum.The sensitivity of fish to current is high - up to 1 μV / cm2: carp feels the current with a voltage of 0.06 ... 0.1, trout - 0.02 ... 0.08, crucian carp 0.008 ... 0, 0015 V. It is assumed that the perception of changes in the electromagnetic field of the Earth allows
It is not possible for fish to detect an approaching earthquake 6...24 hours before the start within a radius of up to 2,000 km.
organs of vision. They are arranged in much the same way as in other vertebrates. The mechanism of perception of visual sensations is also similar to other vertebrates: light passes into the eye through the transparent cornea, then the pupil (hole in the iris) passes it to the lens, and the lens transmits (focuses) the light to the inner wall of the eye (retina), where and its direct perception takes place (Fig. 3). The retina consists of light-sensitive (photoreceptor), nerve and supporting cells.

Light-sensitive cells are located on the side of the pigment membrane. In their processes, shaped like rods and cones, there is a photosensitive pigment. The number of these photoreceptor cells is very large: there are 50 thousand of them per 1 mm 2 of the retina in carp, 162 thousand in squid, 16 in spiders, and 400 thousand in humans. Through a complex system of contacts between the terminal branches of sensory cells and dendrites of nerve cells, light stimuli enter the optic nerve.
Cones in bright light perceive the details of objects and color: they capture the long wavelengths of the spectrum. Rods perceive weak light, but they 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, the pigment cells expand and cover the rods located near them; cones are drawn to the nuclei of cells and thus move towards the light. In the dark, sticks are drawn to the nuclei and are closer to the surface; the cones approach the pigment layer, and the pigment cells reduced in the dark cover them.
The number of receptors of various kinds depends on the way of life of fish. In diurnal fish, cones prevail in the retina, in twilight and nocturnal fish, rods: in burbot, there are 14 times more rods than in pike. Deep-sea fish living 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 probability of capturing even weak light increases. Most fish see colors. Some features in the structure of the eyes of fish are associated with the characteristics of life in the water. They are elliptical in shape and have a silvery shell between the vascular and protein, rich in guanine crystals, which gives the eye a greenish-golden sheen. cornea
fish is almost flat (rather than convex), the lens is spherical (rather than biconvex) - this expands the field of view. A hole in the iris (pupil) can change diameter only within small limits. As a rule, fish do not have eyelids. Only sharks have a nictitating membrane that covers the eye like a curtain, and some herring and mullet have an adipose eyelid—a transparent film covering part of the eye.
The location of the eyes in most species on the sides of the head is the reason why fish have mostly monocular vision, and the ability for binocular vision is limited. The spherical shape of the lens and its movement forward to the cornea provides a wide field of view: light enters the eye from all sides. The vertical angle of view is 150°, horizontally 168...170°. But at the same time, the sphericity of the lens causes myopia in fish. The range of their vision is limited and fluctuates due to the turbidity of the water from a few centimeters to several tens of meters. Long-distance vision becomes possible due to the fact that the lens can be pulled back by a special muscle, a crescent-shaped process extending from the choroid of the bottom of the eyecup, and not due to a change in the curvature of the lens, as in mammals.
With the help of vision, fish are also guided by objects on the ground.
Improved vision in the dark is achieved by the presence of a reflective layer (tapetum) - guanine crystals, underlain by pigment. This layer t transmits light to the tissues lying behind the retina, and reflects it and returns it again.
on the retina. This increases the ability of the receptors to use the light that has entered the eye.
Due to habitat conditions, the eyes of fish can change greatly. In cave or abyssal (deep water) 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 put in parallel and gain binocular vision. The eyes of some eels and larvae of tropical fish are brought forward on long outgrowths (stalked eyes). An unusual modification of the eyes of a four-eyed bird that lives in the waters of Central and South America. Her eyes are placed on top of her 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. In the air, the eyes of fish crawling out onto land can function.
In addition to the eyes, the pineal gland (an endocrine gland) and photosensitive cells located in the tail part, 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 food, maintaining a flock, during the spawning period (perception of defensive and aggressive postures and movements by rival males, and between individuals of different sexes - mating attire and spawning "ceremonial"), in the relationship of the victim-predator, 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., different colors. So, bright artificial light attracts some fish (Caspian sprat, saury, horse mackerel, mackerel) and scares away others (mullet, lamprey, eel). In the same way, different species are selectively related to different colors and different sources of light, surface and underwater. All this is the basis for the organization of industrial fishing for electric light. This is how sprat, saury and other fish are caught.
Organ of hearing and balance of fish. It is located in the back of the skull and is represented by a labyrinth. There are no ear openings, auricle and cochlea, i.e., the organ of hearing is represented by the inner ear.
It reaches the 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 distinguishes between the upper part - an oval pouch (ear, utriculus) and the lower one - a round pouch (sacculus). From the top. parts in mutually perpendicular directions depart three semicircular canals, each of which at one end is expanded into an ampulla

An oval sac with semicircular canals constitutes the organ of balance (vestibular apparatus). The lateral expansion of the lower part of the round pouch (lagena), which is the rudiment of the cochlea, does not receive further development in fish. An internal lymphatic (endolymphatic) canal departs from the round sac, which in sharks and rays goes out through a special hole in the skull, and in other fish it ends blindly at the scalp.
The epithelium lining the sections of the labyrinth has sensory cells with hairs extending into the internal cavity. Their bases are braided with branches of the auditory nerve.
The cavity of the labyrinth is filled with endolymph, it contains "auditory" pebbles, consisting of carbonic lime (otoliths), three on each side of the head: in oval and round sacs and lagen. On otoliths, as on scales, concentric layers are formed; therefore, otoliths, especially the largest one, 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 the round sac, but in cyprinids and some others, in the lagen.
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 side of the otolith, changes, and the resulting irritation is captured by the nerve endings. With the experimental destruction of the upper part of the labyrinth with semicircular canals, the fish loses the ability to maintain balance and lies on its side, back or belly. The destruction of the lower part of the labyrinth does not lead to a 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 lagen fish are removed, they cannot distinguish sound tones, for example, when developing conditioned reflexes. Fish without an oval pouch and semicircular canals, that is, without the upper part of the labyrinth, are amenable to training. Thus, it has been established that the round sac and lagena are sound receptors.
Fish perceive both mechanical and sound vibrations with a frequency of 5 to 25 Hz by the organs of the lateral line, from 16 to 13,000 Hz by the labyrinth. Some species of fish pick up vibrations that are on the border of infrasonic waves with the lateral line, labyrinth and skin receptors.
Hearing acuity in fish is less than in higher vertebrates, and varies among different species: ide perceives vibrations with a wavelength of 25 ... 5524 Hz, silver carp - 25 ... 3840, eel - 36 ... 650 Hz , and low sounds are captured by them better. Sharks can 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 a sound is 99.9% reflected by the surface of the water and, therefore, only 0.1% of the resulting sound waves penetrate the water.
In the perception of sound in cyprinids and catfish, an important role is played by the swim bladder, connected to the labyrinth and serving as a resonator.
Fish can make their own sounds. Sound-producing organs in 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 (soma), jaw and pharyngeal teeth (perch and cyprinids), etc. In this regard, the nature of the sounds is not the same. They may resemble beats, clatters, whistles, grunts, grunts, squeaks, croaks, growls, crackles, rumbles, ringing, wheezing, horns, bird calls, and insect chirps.
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, save the flock, inform relatives about the presence of food, protect the territory, nest and offspring from enemies, is a maturation stimulator during mating games, that is, it serves as an important means of communication. It is assumed that in deep-sea fish dispersed in the dark at the depths of the ocean, it is hearing, in combination with the organs of the lateral line and the sense of smell, that provides communication, especially since the sound conductivity, which is higher in water than in air, increases at depth. Hearing is especially important for nocturnal fish and inhabitants of muddy waters.
The reaction of different fish to extraneous sounds is different: with noise, some go to the side, others (silver carp, salmon, mullet) jump out of the water. This is used in the organization of fishing. In fish farms, during the spawning period, traffic near the spawning ponds is prohibited.

Endocrine glands

The endocrine glands are the pituitary, pineal, adrenal, 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 underside of the diencephalon (hypothalamus). Its shape, 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 silver carp, 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 brain (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), which is formed from an invagination of the upper pharyngeal wall. In the adenohypophysis, three parts (lobes, lobes) are distinguished: the 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, its shares produce a secret containing a number of hormones that stimulate growth (a somatic hormone is necessary for bone growth), regulate the functions of the gonads and thus affect puberty, affect the activity of pigment cells (determine the color of the body and, above all, the appearance of marriage attire ) and increase the resistance of fish to high temperatures, stimulates protein synthesis, the functioning of the thyroid gland, and participates in osmoregulation. Removal of the pituitary gland entails a cessation of growth and maturation.
Hormones secreted by the neurohypophysis are synthesized in the nuclei of the hypothalamus and are transported along the nerve fibers to the neurohypophysis, and then enter the capillaries penetrating it. Thus, this is a neutrosecretory gland. Hormones take part in osmoregulation, cause spawning reactions.
A single system with the pituitary gland is formed by the hypothalamus, whose cells 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 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 in the glandular cells accumulates almost simultaneously "after the secretion is removed, by the time of ovulation the pituitary gland is emptied, and there is a break in its secretory activity. reception and thus constitute a single generation,
In batch spawning fish, the secret in the cells is formed non-simultaneously. As a result, after the release of the secret during the first spawning, there remains a part of the cells in which the process of colloid formation has not ended. As a result, it can be released in portions throughout the entire spawning period. In turn, oocytes prepared for littering 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 first generation of oocytes, i.e., the first portion of caviar, has been hatched. This is how several servings of caviar are formed.
The study of 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 develop a method of pituitary injections to producers to speed up their maturation. This method made it possible to largely control the process of maturation of fish and thereby increase the scope of fish breeding work on the reproduction of valuable species. Pituitary injections are widely used in the artificial breeding of sturgeon and cyprinids.
The third neurosecretory division of the diencephalon. - Pineal gland. Its hormones (serotin, melatonin, adrenoglomerulotropin) are involved in seasonal metabolic changes. Its activity is affected by illumination and daylight hours: with their increase, fish activity 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 pair formation, consisting of follicles that secrete hormones, in others (perch, carp) glandular cells do not form a formalized 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 almost ends. Follicles containing colloid are found in 4-day-old larvae of stellate sturgeon.
In the future, the gland periodically secretes an accumulating secret, 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 attire. The maximum activity coincides with the moment of ovulation.
The activity of the thyroid gland changes throughout life, gradually falling in the process of aging, and also depending on the availability of food for the fish: underfeeding causes an increase in function.
In females, the thyroid gland is more developed than in males, but in males it is more active.
The thyroid gland plays an important role in the regulation of metabolism, the processes of growth and differentiation, carbohydrate metabolism, osmoregulation, maintaining the normal activity of the nerve centers, the adrenal cortex, and the sex glands. The addition of a thyroid preparation to the feed accelerates the development of juveniles. When the thyroid function is impaired, a goiter appears.
Sex glands - ovaries and testes secrete sex hormones. Their secretion is periodic: the greatest amount of hormones is formed during the period of maturity of the gonads. These hormones are associated with the appearance of marriage attire.
In the ovaries of sharks and river eels, as well as in the blood plasma of sharks, the hormones 17N-estradiol and esterone were found, localized mainly in the eggs, less in the ovarian tissue. Deoxycorticosterone and progesterone have been found in male sharks and salmon.
In fish, there is a relationship between the pituitary, thyroid and gonads. In the pre-spawning and spawning periods, the maturation of the gonads is directed by the activity of the pituitary and thyroid glands, and the activity of these glands is also interconnected.
The pancreas in bony fish performs a dual function—external (enzyme secretion) and internal (insulin secretion) glands.
The formation of insulin is localized in the islets of Langerhans interspersed in the liver tissue. It plays an important role in the regulation of carbohydrate metabolism and protein synthesis.
Ultimobranchial (supraperibranchial or subesophageal) glands have been 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. The cells of the glands secrete the hormone calcitonin, which prevents the resorption of calcium from the bones and thus prevents its concentration in the blood from rising.
Adrenals. Unlike higher animals in fish, the medulla and cortex are separated and do not form a single organ. In bony fish, they are located in different parts of the kidney. The cortical substance (corresponding to the cortical tissue of higher vertebrates) is embedded in the anterior part of the kidney and is called the interrenal tissue. The same substances were found in it as in other vertebrates, but the content, for example, of lipids, phospholipids, cholesterol, ascorbic acid, is higher in fish.
Hormones of the cortical layer have a multifaceted effect on the vital activity of the body. So, glucocorticoids (cortisol, cortisone, 11-deoxycortisol were found in fish) and sex hormones are involved in the development of the skeleton, muscles, sexual behavior, and carbohydrate metabolism. Removal of interrenal tissue leads to respiratory arrest even before cardiac arrest. Cortisol is involved in osmoregulation.
The medulla of the adrenal glands in higher animals in fish corresponds to chromaffin tissue, individual cells of which are scattered and tissues of the kidneys. The hormone adrenaline secreted by them affects the vascular and muscular systems, increases the excitability and strength of the pulsation of the heart, causes the expansion and narrowing of blood vessels. An increase in the concentration of adrenaline in the blood causes a feeling of anxiety.
The urohypophysis, located in the caudal region of the spinal cord and involved in osmoregulation, is also a neurosecretory and endocrine organ in bony fish, which has a great influence on the functioning of the kidneys.

Poisonousness and poisonousness of fish

Venomous fish have a venomous 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 is different: from the formation of an abscess at the injection site to respiratory and cardiac disorders and death (in severe cases of Trachurus infection). In our seas, the sea dragon (scorpion), stargazer (sea cow), sea ruff (scorpionfish), stingray, sea cat, spiny katran shark), kerchak, sea bass, ruff-nosar, aukha (Chinese ruff), are poisonous. sea mouse (lyre), high beam perch.

When eaten, these fish are harmless.

Fish whose tissues and organs are chemically poisonous are classified as poisonous and should not be eaten. They are especially numerous in the tropics. The liver of the shark Carcharinus glaucus is poisonous, while the puffer Tetradon has poisonous ovaries and eggs. In our fauna, in the marinka Schizothorax and the osman Diptychus, caviar and peritoneum are poisonous, in the barbel Barbus and the templar Varicorhynus, the caviar has a laxative effect. The poison of poisonous fish acts on the respiratory and vasomotor centers, and is not destroyed by boiling. Some fish have poisonous blood (eels Muraena, Anguilla, Conger, lamprey, tench, tuna, carp, etc.). Poisonous properties are shown at an injection of blood serum of these fishes; they disappear when heated, under the action of acids and alkalis.

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

The structure and physiological characteristics of fish

table of contents

Body shape and methods of movement

The skin of fish

Digestive system

Respiratory system and gas exchange (New)

Circulatory system

Nervous system and sense organs

Endocrine glands

Poisonousness and poisonousness of fish

The shape of the body of fish and the ways of movement of fish

The shape of the body should provide the fish with the opportunity to move in water (an environment much denser than air) with the least expenditure of energy and at a speed corresponding to its vital needs. The shape of the body that meets these requirements has developed in fish as a result of evolution: a smooth body without protrusions, covered with mucus, facilitates movement; no neck; a pointed head with pressed gill covers and clenched jaws cuts through the water; the fin system determines the movement in the right direction. According to lifestyle, up to 12 different types of body shape are distinguished

Rice. 1 - garfish; 2 - mackerel; 3 - bream; 4 - moon fish; 5 - flounder; 6 - eel; 7 - fish-needle; 8 - herring king; 9 - slope; 10 - hedgehog fish; 11 - bodywork; 12 - grenadier.

Arrow-shaped - the bones of the snout are elongated and pointed, the body of the fish has the same height along the entire length, the dorsal fin is related to the caudal and is located above the anal, which creates an imitation of the plumage of an arrow. This form is typical for fish that do not travel long distances, stay in ambush and develop high speeds of movement for a short period of time due to the push of the fins when throwing at prey or avoiding a predator. These are pikes (Esox), garfish (Belone), etc. Torpedo-shaped (it is often called spindle-shaped) - characterized by a pointed head, rounded, oval-shaped body in cross section, thinned caudal peduncle, often with additional fins. It is characteristic of good swimmers capable of long-term movements - tuna, salmon, mackerel, sharks, etc. These fish are able to swim for a long time, so to speak, at a cruising speed of 18 km per hour. Salmon are capable of jumping two to three meters when overcoming obstacles during spawning migrations. The maximum speed that a fish can develop is 100-130 km per hour. This record belongs to the sailfish. The body is symmetrically compressed laterally - strongly laterally compressed, high with a relatively short length and high. These are fish of coral reefs - bristle teeth (Chaetodon), thickets of bottom vegetation - angelfish (Pterophyllum). This body shape helps them to easily maneuver among obstacles. Some pelagic fish also have a symmetrically laterally compressed body shape, which needs to quickly change position in space to disorientate predators. The moonfish (Mola mola L.) and bream (Abramis brama L.) have the same body shape. The body is asymmetrically compressed from the sides - the eyes are shifted to one side, which creates an asymmetry of the body. It is characteristic of demersal sedentary fish of the Flounder-like order, helping them to camouflage themselves well at the bottom. In the movement of these fish, an important role is played by the wavy bending of the long dorsal and anal fins. Flattened in the dorsoventral direction, the body is strongly compressed in the dorsal-abdominal direction, as a rule, the pectoral fins are well developed. Sedentary bottom fish have this body shape - most rays (Batomorpha), monkfish (Lophius piscatorius L.). The flattened body camouflages the fish in bottom conditions, and the eyes located on top help to see the prey. Eel-shaped - the body of the fish is elongated, rounded, having the appearance of an oval in a cross section. The dorsal and anal fins are long, there are no pelvic fins, and the caudal fin is small. It is characteristic of bottom and bottom fish, such as eels (Anguilliformes), which move by bending their bodies laterally. Ribbon-shaped - the body of the fish is elongated, but unlike the eel-shaped form, it is strongly compressed from the sides, which provides a large specific surface area and allows the fish to live in the water column. The nature of their movement is the same as that of eel-shaped fish. This body shape is typical for saber fish (Trichiuridae), herring king (Regalecus). Macro-shaped - the body of the fish is high in the front, narrowed from the back, especially in the tail section. The head is large, massive, the eyes are large. It is characteristic of deep-sea sedentary fish - macrourus-like (Macrurus), chimeric (Chimaeriformes). Asterolepid (or body-shaped) - the body is enclosed in a bony shell, which provides protection from predators. This body shape is characteristic of benthic inhabitants, many of which are found in coral reefs, such as boxfish (Ostracion). The spherical shape is characteristic of some species from the Tetraodontiformes order - the ball fish (Sphaeroides), the hedgehog fish (Diodon), etc. These fish are poor swimmers and move with the help of undulating (wave-like) movements of the fins over short distances. When threatened, fish inflate the intestinal air sacs, filling them with water or air; at the same time, the spikes and spines on the body are straightened, protecting them from predators. The needle-shaped body shape is characteristic of marine needles (Syngnathus). Their elongated body, hidden in a bone shell, imitates the leaves of the zoster, in the thickets of which they live. The fish lack lateral mobility and move with the help of the undulating (wave-like) action of the dorsal fin. Often there are fish whose body shape resembles simultaneously different types of forms. To eliminate the unmasking shadow on the belly of the fish that occurs when illuminated from above, small pelagic fish, such as herring (Clupeidae), sabrefish (Pelecus cultratus (L.)], have a pointed, laterally compressed abdomen with a sharp keel. Large mobile pelagic predators have mackerel (Scomber), swordfish (Xiphias gladius L.), tuna (Thunnus) - usually do not develop a keel.Their method of defense is speed of movement, not camouflage.In demersal fish, the cross-sectional shape approaches an isosceles trapezium facing large base down, which eliminates the appearance of shadows on the sides when illuminated from above.Therefore, most demersal fish have a wide flattened body.

SKIN, SCALES AND LUMINOSIS

Rice. Fish scale shape. a - placoid; b - ganoid; c - cycloid; d - ctenoid

Placoid - the most ancient, preserved in cartilaginous fish (sharks, rays). It consists of a plate on which a spine rises. Old scales are discarded, new ones appear in their place. Ganoid - mainly in fossil fish. The scales are rhombic in shape, closely articulated with each other, so that the body is enclosed in a shell. Scales do not change over time. The scales owe their name to ganoin (dentine-like substance), which lies in a thick layer on the bone plate. Among modern fish, armored pikes and multifins have it. In addition, sturgeons have it in the form of plates on the upper lobe of the caudal fin (fulcra) and scutes scattered over the body (a modification of several merged ganoid scales). Gradually changing, the scales lost ganoin. Modern bony fish no longer have it, and the scales consist of bony plates (bone scales). These scales can be cycloid - rounded, with smooth edges (cyprinids) and ctenoid with a serrated trailing edge (percids). Both forms are related, but the cycloid, as a more primitive one, is found in low-organized fish. There are cases when, within the same species, males have ctenoid scales, and females have cycloid scales (flounders of the genus Liopsetta), or even scales of both forms are found in one individual. The size and thickness of the scales in fish vary greatly - from microscopic scales of an ordinary eel to very large, palm-sized scales of a three-meter long barbel that lives in Indian rivers. Only a few fish do not have scales. In some, it merged into a solid, immovable shell, like a boxfish, or formed rows of closely connected bone plates, like seahorses. Bone scales, like ganoid scales, are permanent, do not change and only increase annually in accordance with the growth of the fish, and distinct annual and seasonal marks remain on them. The winter layer has more frequent and thin layers than the summer one, so it is darker than the summer one. By the number of summer and winter layers on the scales, one can determine the age of some fish. Under the scales, many fish have silvery crystals of guanine. Washed from scales, they are a valuable substance for obtaining artificial pearls. Glue is made from fish scales. On the sides of the body of many fish, one can observe a number of prominent scales with holes that form the lateral line - one of the most important sense organs. The amount of scales in the lateral line - In the unicellular glands of the skin, pheromones are formed - volatile (odorous) substances released into the environment and affecting the receptors of other fish. They are specific to different species, even closely related ones; in some cases, their intraspecific differentiation (age, sex) was determined. In many fish, including cyprinids, the so-called fear substance (ichthyopterin) is formed, which is released into the water from the body of a wounded individual and is perceived by its relatives as a signal announcing danger. Fish skin regenerates quickly. Through it, on the one hand, a partial release of the end products of metabolism occurs, and on the other hand, the absorption of certain substances from the external environment (oxygen, carbonic acid, water, sulfur, phosphorus, calcium and other elements that play a large role in life). The skin also plays an important role as a receptor surface: it contains thermo-, baro-, chemo- and other receptors. In the thickness of the corium, the integumentary bones of the skull and pectoral fin belts are formed. Through the muscle fibers of the myomers connected to its inner surface, the skin participates in the work of the trunk and tail muscles.

Muscular system and electrical organs

The muscular system of fish, like other vertebrates, is divided into the muscular system of the body (somatic) and internal organs (visceral).

In the first, the muscles of the trunk, head and fins are isolated. Internal organs have their own muscles. The muscular system is interconnected with the skeleton (support during contraction) and the nervous system (a nerve fiber approaches each muscle fiber, and each muscle is innervated by a specific nerve). Nerves, blood and lymphatic vessels are located in the connective tissue layer of muscles, which, unlike the muscles of mammals, is small. In fish, like other vertebrates, the trunk muscles are most developed. It provides swimming fish. In real fish, it is represented by two large strands located along the body from head to tail (large lateral muscle - m. lateralis magnus) (Fig. 1). This muscle is divided by a longitudinal connective tissue layer into dorsal (upper) and abdominal (lower) parts.

Rice. 1 Musculature of bony fish (according to Kuznetsov, Chernov, 1972):

1 - myomers, 2 - myosepts

The lateral muscles are divided by myosepts into myomers, the number of which corresponds to the number of vertebrae. Myomeres are most clearly visible in fish larvae, while their bodies are transparent. The muscles of the right and left sides, contracting alternately, bend the caudal section of the body and change the position of the caudal fin, due to which the body moves forward. Above the large lateral muscle along the body between the shoulder girdle and tail in sturgeons and teleosts lies the rectus lateral superficial muscle (m. rectus lateralis, m. lateralis superficialis). In salmon, a lot of fat is deposited in it. The rectus abdominis (m. rectus abdominalis) stretches along the underside of the body; some fish, such as eels, do not. Between it and the direct lateral superficial muscle are oblique muscles (m. obliguus). The muscle groups of the head control the movements of the jaw and gill apparatus (visceral muscles). The fins have their own muscles. The greatest accumulation of muscles also determines the location of the center of gravity of the body: in most fish it is located in the dorsal part. The activity of the trunk muscles is regulated by the spinal cord and cerebellum, and the visceral muscles are innervated by the peripheral nervous system, which is excited involuntarily.

A distinction is made between striated (acting largely voluntarily) and smooth muscles (which act independently of the will of the animal). The striated muscles include the skeletal muscles of the body (trunk) and the muscles of the heart. Trunk muscles can contract quickly and strongly, but soon get tired. A feature of the structure of the heart muscles is not the parallel arrangement of isolated fibers, but the branching of their tips and the transition from one bundle to another, which determines the continuous operation of this organ. Smooth muscles also consist of fibers, but much shorter and do not exhibit transverse striation. These are the muscles of the internal organs and the walls of blood vessels, which have peripheral (sympathetic) innervation. Striated fibers, and therefore muscles, are divided into red and white, which differ, as the name implies, in color. The color is due to the presence of myoglobin, a protein that readily binds oxygen. Myoglobin provides respiratory phosphorylation, accompanied by the release of a large amount of energy. Red and white fibers are different in a number of morphophysiological characteristics: color, shape, mechanical and biochemical properties (respiratory rate, glycogen content, etc.). Red muscle fibers (m. lateralis superficialis) - narrow, thin, intensively supplied with blood, located more superficially (in most species under the skin, along the body from head to tail), contain more myoglobin in the sarcoplasm; accumulations of fat and glycogen were found in them. Their excitability is less, individual contractions last longer, but proceed more slowly; oxidative, phosphorus and carbohydrate metabolism is more intense than in whites. The heart muscle (red) has little glycogen and a lot of enzymes of aerobic metabolism (oxidative metabolism). It is characterized by a moderate rate of contractions and tires more slowly than white muscles. In wide, thicker, light white fibers m. lateralis magnus myoglobin is small, they have less glycogen and respiratory enzymes. Carbohydrate metabolism occurs predominantly anaerobically, and the amount of energy released is less. Individual cuts are fast. Muscles contract and fatigue faster than red ones. They lie deeper. The red muscles are constantly active. They ensure long-term and uninterrupted functioning of the organs, support the constant movement of the pectoral fins, ensure the bending of the body when swimming and turning, and the continuous work of the heart. With fast movement, throws, white muscles are active, with slow movement, red ones. Therefore, the presence of red or white fibers (muscles) depends on the mobility of the fish: "sprinters" have almost exclusively white muscles, in fish that are characterized by long migrations, in addition to the red lateral muscles, there are additional red fibers in the white muscles. The bulk of the muscle tissue in fish is made up of white muscles. For example, in asp, roach, sabrefish, they account for 96.3; 95.2 and 94.9% respectively. White and red muscles differ in chemical composition. Red muscles contain more fat, while white muscles contain more moisture and protein. The thickness (diameter) of the muscle fiber varies depending on the type of fish, their age, size, lifestyle, and in pond fish - on the conditions of detention. For example, in a carp grown on natural food, the diameter of the muscle fiber is (μm): in fry - 5 ... 19, underyearlings - 14 ... 41, two-year-olds - 25 ... 50. The trunk muscles form the main share of fish meat . Meat yield as a percentage of total body weight (meatiness) is not the same in different species, and in individuals of the same species it varies depending on sex, conditions of detention, etc. Fish meat is digested faster than the meat of warm-blooded animals. It is often colorless (perch) or has shades (orange in salmon, yellowish in sturgeon, etc.), depending on the presence of various fats and carotenoids. The bulk of fish muscle proteins are albumins and globulins (85%), in total, 4 ... 7 protein fractions are isolated from different fish. The chemical composition of meat (water, fats, proteins, minerals) is different not only in different species, but also in different parts of the body. In fish of the same species, the amount and chemical composition of meat depend on the nutritional conditions and the physiological state of the fish. During the spawning period, especially in migratory fish, reserve substances are consumed, depletion is observed and, as a result, the amount of fat decreases and the quality of meat deteriorates. In chum salmon, for example, during the approach to spawning grounds, the relative mass of bones increases by 1.5 times, skin - by 2.5 times. Muscles are hydrated - the dry matter content is reduced by more than two times; fat and nitrogenous substances practically disappear from the muscles - the fish loses up to 98.4% of fat and 57% of protein. Features of the environment (primarily food and water) can greatly change the nutritional value of fish: in swampy, muddy or oil-polluted water bodies, fish have meat with an unpleasant odor. The quality of meat also depends on the diameter of the muscle fiber, as well as the amount of fat in the muscles. To a large extent, it is determined by the ratio of the mass of muscle and connective tissues, which can be used to judge the content of full-fledged muscle proteins in the muscles (compared to defective proteins of the connective tissue layer). This ratio varies depending on the physiological state of the fish and environmental factors. In the muscle proteins of bony fish, proteins account for: sarcoplasms 20 ... 30%, myofibrils - 60 ... 70, stroma - about 2%. All the variety of body movements is provided by the work of the muscular system. It mainly provides the release of heat and electricity in the body of the fish. An electric current is formed when a nerve impulse is conducted along a nerve, with a contraction of myofibrils, irritation of photosensitive cells, mechanochemoreceptors, etc. Electric organs

Electric organs are peculiarly altered muscles. These organs develop from the rudiments of striated muscles and are located on the sides of the fish body. They consist of many muscle plates (there are about 6000 in electric eel), converted into electrical plates (electrocytes), interbedded with gelatinous connective tissue. The bottom of the plate is negatively charged, the top is positively charged. Discharges occur under the influence of impulses of the medulla oblongata. As a result of discharges, water decomposes into hydrogen and oxygen, therefore, for example, in the overseas reservoirs of the tropics, small inhabitants accumulate near electric fish - mollusks, crustaceans, attracted by more favorable breathing conditions. Electric organs can be located in different parts of the body: for example, in the sea fox stingray - on the tail, in the electric catfish - on the sides. By generating electric current and perceiving lines of force distorted by objects encountered on the way, fish navigate in the stream, detect obstacles or prey from a distance of several meters, even in muddy water. In accordance with the ability to generate electric fields, fish are divided into three groups: 1. Strongly electric species - they have large electric organs that generate discharges from 20 to 600 and even 1000 V. The main purpose of the discharges is attack and defense (electric eel, electric stingray, electric catfish). 2. Weakly electric species - have small electric organs that generate discharges with a voltage of less than 17 V. The main purpose of the discharges is location, signaling, orientation (many mormirids, hymnotids, and some rays that live in the muddy rivers of Africa). 3. Non-electric species - do not have specialized organs, but have electrical activity. The discharges generated by them extend to 10 ... 15 m in sea water and up to 2 m in fresh water. The main purpose of the generated electricity is location, orientation, signaling (many marine and freshwater fish: for example, horse mackerel, sable, perch, etc.).

Of the 40-41 thousand species of vertebrates that exist on earth, fish is the most species-rich group: it has over 20 thousand living representatives. Such a variety of species is explained, first of all, by the fact that fish are one of the most ancient animals on earth - they appeared 400 million years ago, that is, when there were no birds, amphibians, or mammals on the globe . During this period, fish have adapted to live in a wide variety of conditions: they live in the World Ocean, at depths of up to 10,000 m, and in alpine lakes, at an altitude of up to 6,000 m, some of them can live in mountain rivers, where the water speed reaches 2 m / s, and others - in stagnant water bodies.

Of the 20 thousand species of fish, 11.6 thousand are marine, 8.3 thousand are freshwater, and the rest are anadromous. All fish belonging to a number of fish, on the basis of their similarity and relationship, are divided according to the scheme developed by the Soviet academician L. S. Berg into two classes: cartilaginous and bone. Each class consists of subclasses, subclasses of superorders, superorders of orders, orders of families, families of genera, and genera of species.

Each species has characteristics that reflect its adaptability to certain conditions. All individuals of a species can interbreed and produce offspring. Each species in the process of development has adapted to the known conditions of reproduction and nutrition, temperature and gas conditions, and other factors of the aquatic environment.

The shape of the body is very diverse, which is caused by the adaptation of fish to various, sometimes very peculiar, conditions of the aquatic environment (Fig. 1.). The following forms are most common: torpedo-shaped, arrow-shaped, ribbon-shaped, eel-shaped, flat and spherical.

The body of the fish is covered with skin, which has the upper layer - the epidermis and the lower - the corium. The epidermis consists of a large number of epithelial cells; in this layer there are mucus secretion, pigment, luminous and poisonous glands. The corium, or skin proper, is a connective tissue permeated with blood vessels and nerves. There are also clusters of large pigment cells and guanine crystals, which give the skin of fish a silvery color.

In most fish, the body is covered with scales. It does not exist in fish swimming at low speeds. The scales ensure the smoothness of the surface of the body and prevent the appearance of skin folds on the sides.

Freshwater fish have bony scales. According to the nature of the surface, two types of bony scales are distinguished: cycloid with a smooth posterior edge (cyprinids, herring) and ctenoid, the posterior edge of which is armed with spines (perch). The age of bony fish is determined from annual rings of bony scales (Fig. 2).

The age of the fish is also determined by the bones (bones of the gill cover, jawbone, large integumentary bone of the shoulder girdle - cleistrum, sections of hard and soft rays of the fins, etc.) and otoliths (calcareous formations in the ear capsule), where, as on the scales, stratifications corresponding to the annual cycles of life.

The body of sturgeon fish is covered with a special type of scales - bugs, they are located on the body in longitudinal rows, have a conical shape.

The skeleton of fish can be cartilaginous (sturgeon and lampreys) and bone (all other fish).

Fish fins are: paired - pectoral, ventral and unpaired - dorsal, anal, caudal. The dorsal fin can be one (for cyprinids), two (for perch) and three (for cod). The adipose fin without bony rays is a soft skin outgrowth on the back of the back (in salmon). The fins provide balance to the body of the fish and its movement in different directions. The caudal fin creates a driving force and acts as a rudder, providing maneuverability of the fish when turning. The dorsal and anal fins support the normal position of the body of the fish, that is, they act as a keel. Paired fins maintain balance and are rudders of turns and depth (Fig. 3).

The respiratory organ is the gills, which are located on both sides of the head and are covered with covers. When breathing, the fish swallows water through the mouth and pushes it out through the gills. Blood from the heart enters the gills, enriched with oxygen, and spreads through the circulatory system. Carp, crucian carp, catfish, eel, loach and other fish that inhabit lake water bodies, where oxygen is often lacking, are able to breathe with their skin. In some fish, the swim bladder, intestines, and special additional organs are able to use atmospheric oxygen. So, snakehead, basking in shallow water, can breathe air through the supragillary organ. The circulatory system of fish consists of the heart and blood vessels. Their heart is two-chambered (has only an atrium and a ventricle), directs venous blood through the abdominal aorta to the gills. The most powerful blood vessels run along the spine. Fish have only one circulation. The digestive organs of fish are the mouth, pharynx, esophagus, stomach, liver, intestines, ending in the anus.

The shape of the mouth in fish is varied. Plankton-feeding fish have an upper mouth, bottom-feeding fish have a lower mouth, and predatory fish have a terminal mouth. Many fish have teeth. Carp fish have pharyngeal teeth. Behind the mouth of the fish is the oral cavity, where food initially enters, then it goes to the pharynx, esophagus, stomach, where it begins to be digested under the action of gastric juice. Partially digested food enters the small intestine, where the ducts of the pancreas and liver flow. The latter secretes bile, which accumulates in the gallbladder. Carp fish do not have a stomach, and food is digested in the intestines. Undigested food remains are excreted into the hindgut and through the anus are removed to the outside.

The excretory system of fish serves to remove metabolic products and ensure the water-salt composition of the body. The main organs of excretion in fish are the paired trunk kidneys with their excretory ducts - the ureters, through which urine enters the bladder. To some extent, the skin, gills and intestines take part in excretion (removal of end products of metabolism from the body).

The nervous system is divided into the central, which includes the brain and spinal cord, and the peripheral - the nerves extending from the brain and spinal cord. Nerve fibers depart from the brain, the endings of which come to the surface of the skin and form in most fish a pronounced lateral line that runs from the head to the beginning of the rays of the caudal fin. The lateral line serves to orient the fish: determine the strength and direction of the current, the presence of underwater objects, etc.

The organs of vision - two eyes - are located on the sides of the head. The lens is round, does not change shape and almost touches the flat cornea, therefore the fish are short-sighted: most of them distinguish objects at a distance of up to 1 m, and at most 1 they see no more than 10-15 m.

The nostrils are located in front of each eye, leading to a blind olfactory sac.

The organ of hearing of fish is also an organ of balance, it is located in the back of the skull, a cartilaginous, or bone, chamber: it consists of upper and lower sacs in which otoliths are located - pebbles consisting of calcium compounds.

Taste organs in the form of microscopic taste cells are located in the membrane of the oral cavity and on the entire surface of the body. Fish have a well-developed sense of touch.

The reproductive organs in females are the ovaries (ovaries), in males - the testes (milk). Inside the ovary there are eggs, which in different fish have different sizes and colors. The caviar of most fish is edible and is a highly valuable food product. Sturgeon and salmon caviar is distinguished by the highest nutritional quality.

The hydrostatic organ that provides buoyancy to fish is a swim bladder filled with a mixture of gases and located above the entrails. Some demersal fish lack a swim bladder.

The temperature sense of fish is associated with receptors located in the skin. The simplest reaction of fish to a change in water temperature is to move to places where the temperature is more favorable for them. Fish do not have mechanisms of thermoregulation, their body temperature is unstable and corresponds to the temperature of the water or differs slightly from it.

Fish and the environment

Not only different types of fish live in the water, only different types of fish, but also thousands of living beings, plants and microscopic organisms. Reservoirs where fish live differ from each other in physical and chemical properties. All these factors affect the biological processes occurring in the water and, consequently, the life of fish.

The relationship of fish with the environment is combined into two groups of factors: abiotic and biotic.

Biotic factors include the world of animal and plant organisms that surround the fish in the water and act on it. This also includes intraspecific and interspecific relationships of fish.

The physical and chemical properties of water (temperature, salinity, gas content, etc.) that affect fish are called abiotic factors. Abiotic factors also include the size of the reservoir and its depth.

Without knowledge and study of these factors, it is impossible to successfully engage in fish farming.

The anthropogenic factor is the impact of human economic activity on the reservoir. Land reclamation increases the productivity of water bodies, while pollution and water abstraction reduce their productivity or turn them into dead water bodies.

Abiotic factors of water bodies

The aquatic environment where the fish lives has certain physical and chemical properties, the change of which is reflected in the biological processes occurring in the water, and, consequently, in the life of fish and other living organisms and plants.

Water temperature. Different types of fish live at different temperatures. So, in the mountains of California, the lukaniye fish lives in warm springs at a water temperature of + 50 ° C and above, and crucian carp spend the winter in hibernation at the bottom of a frozen reservoir.

Water temperature is an important factor for the life of fish. It affects the timing of spawning, development of eggs, growth rate, gas exchange, digestion.

Oxygen consumption is directly dependent on water temperature: when it decreases, oxygen consumption decreases, and when it increases, it increases. The temperature of the water also affects the nutrition of fish. With its increase, the rate of digestion of food in fish increases, and vice versa. So, carp feeds most intensively at water temperature +23...+29°C, and at +15...+17°C it reduces its nutrition by three to four times. Therefore, pond farms constantly monitor the water temperature. In fish farming, pools at thermal and nuclear power plants, underground thermal waters, warm sea currents, etc. are widely used.

The fish of our reservoirs and seas are divided into heat-loving (carp, sturgeon, catfish, eels) and cold-loving (cod and salmon). In the reservoirs of Kazakhstan, mainly heat-loving fish live, with the exception of bred new fish, such as trout and whitefish, which are cold-loving. Some species - crucian carp, pike, roach, marinka and others - withstand fluctuations in water temperature from 20 to 25 ° C.

Heat-loving fish (carp, bream, roach, catfish, etc.) in winter concentrate in areas of the deep zone determined for each species, they show passivity, their feeding slows down or stops completely.

Fish that lead an active lifestyle in the winter (salmon, whitefish, pike perch, etc.) are cold-loving.

The distribution of commercial fish in large bodies of water usually depends on the temperature in different parts of this body of water. It is used for fishing and commercial reconnaissance.

Salinity of water also acts on fish, although most of them withstand its vibrations. The salinity of water is defined in thousandths: 1 ppm is equal to 1 g of dissolved salts in 1 liter of sea water, and it is indicated by the sign ‰. Some fish species can withstand water salinity up to 70‰, i.e. 70 g/l.

According to the habitat and in relation to the salinity of the water, fish are usually divided into four groups: marine, freshwater, anadromous and brackish-water.

Marine include fish that live in the oceans and coastal sea waters. Freshwater fish constantly live in fresh water. Anadromous fish for breeding either move from sea water to fresh water (salmon, herring, sturgeon) or from fresh water to sea water (some eels). Brackish-water fish live in desalinated areas of the seas and in inland seas with low salinity.

For fish living in lake reservoirs, ponds and rivers, it is important the presence of gases dissolved in water- oxygen, hydrogen sulfide and other chemical elements, as well as the smell, color and taste of water.

An important indicator for the life of fish is amount of dissolved oxygen in water. For carp fish, it should be 5-8, for salmon - 8-11 mg / l. When the oxygen concentration decreases to 3 mg/l, the carp feels bad and eats worse, and at 1.2-0.6 mg/l it can die. When the lake becomes shallow, when the water temperature rises and when it is overgrown with vegetation, the oxygen regime deteriorates. In shallow reservoirs, when their surface is covered with a dense layer of ice and snow in winter, the access of atmospheric oxygen stops and after a while, usually in March (if you do not make an ice hole), the death of fish begins from oxygen starvation, or the so-called "zamora".

Carbon dioxide plays an important role in the life of a reservoir, is formed as a result of biochemical processes (decomposition of organic matter, etc.), it combines with water and forms carbonic acid, which, interacting with bases, gives bicarbonates and carbonates. The content of carbon dioxide in water depends on the time of year and the depth of the reservoir. In summer, when aquatic plants absorb carbon dioxide, there is very little of it in the water. High concentrations of carbon dioxide are harmful to fish. When the content of free carbon dioxide is 30 mg/l, the fish feeds less intensively, its growth slows down.

hydrogen sulfide It is formed in water in the absence of oxygen and causes the death of fish, and the strength of its action depends on the temperature of the water. At high water temperatures, fish quickly die from hydrogen sulfide.

With the overgrowth of reservoirs and the decay of aquatic vegetation, the concentration of dissolved organic substances in the water increases and the color of the water changes. In swampy water bodies (brown water), fish cannot live at all.

Transparency- one of the important indicators of the physical properties of water. In clean lakes, plant photosynthesis proceeds at a depth of 10-20 m, in reservoirs with low-transparent water - at a depth of 4-5 m, and in ponds in the summer, transparency does not exceed 40-60 cm.

The degree of water transparency depends on a number of factors: in rivers - mainly on the amount of suspended particles and, to a lesser extent, on dissolved and colloidal substances; in stagnant water bodies - ponds and lakes - mainly from the course of biochemical processes, for example, from the blooming of water. In any case, the decrease in the transparency of water is associated with the presence of the smallest suspended mineral and organic particles in it. Getting on the gills of fish, they make it difficult for them to breathe.

Pure water is a chemically neutral compound with equally acidic and alkaline properties. Hydrogen and hydroxyl ions are present in equal amounts. Based on this property of pure water, the concentration of hydrogen ions is determined in pond farms; for this purpose, a water pH indicator has been established. When the pH is 7, then this corresponds to the neutral state of water, less than 7 is acidic, and above 7 is alkaline.

In most fresh water bodies, the pH is 6.5-8.5. In summer, with intensive photosynthesis, an increase in pH to 9 and above is observed. In winter, when carbon dioxide accumulates under the ice, its lower values are observed; The pH also changes during the day.

In pond and lake-commodity fish farming, regular monitoring of water quality is established: the pH of the water, color, transparency and its temperature are determined. Each fish farm for conducting hydrochemical water analysis has its own laboratory equipped with the necessary instruments and reagents.

Biotic factors of water bodies

Biotic factors are of great importance for the life of fish. In each reservoir, sometimes dozens of species of fish mutually exist, which differ from each other in the nature of their diet, location in the reservoir, and other characteristics. Distinguish intraspecific, interspecific relationships of fish, as well as the relationship of fish with other aquatic animals and plants.

Intraspecific relations of fish are aimed at ensuring the existence of a species by forming single-species groups: schools, elementary populations, aggregations, etc.

Many fish lead flock image life (Atlantic herring, anchovy, etc.), and most fish gather in flocks only at a certain period (during spawning or feeding). Flocks are formed from fish of a similar biological state and age and are united by the unity of behavior. Schooling is an adaptation of fish to find food, find migration routes, and protect themselves from predators. A school of fish is often called a school. However, there are some species that do not gather in flocks (catfish, many sharks, lumpfish, etc.).

An elementary population represents a grouping of fish, mostly of the same age, similar in physiological state (fatness, degree of puberty, amount of hemoglobin in the blood, etc.), and persists for life. They are called elementary because they do not break up into any intraspecific biological groups.

A herd, or population, is a single-species self-reproducing group of fish of different ages, inhabiting a certain area and tied to certain places of reproduction, feeding and wintering.

An accumulation is a temporary association of several schools and elementary fish populations, which is formed as a result of a number of reasons. These include collections:

spawning, arising for reproduction, consisting almost exclusively of sexually mature individuals;

migratory, arising on the ways of movement of fish for spawning, feeding or wintering;

feeding, formed at the places of feeding of fish and caused mainly by the concentration of food objects;

wintering, arising in the wintering places of fish.

Colonies form as temporary protective groups of fish, usually consisting of individuals of the same sex. They are formed at breeding sites to protect egg clutches from enemies.

The nature of the reservoir and the number of fish in it affect their growth and development. So, in small reservoirs, where there are a lot of fish, they are smaller than in large reservoirs. This can be seen in the example of carp, bream and other fish species, which have become larger in the Bukhtarma, Kapchagai, Chardara and other reservoirs than they were before in the former lake. Zaisan, the Balkhash-Ili basin and in the lake reservoirs of the Kzyl-Orda region.

An increase in the number of fish of one species often leads to a decrease in the number of fish of another species. So, in reservoirs where there is a lot of bream, the number of carp is reduced, and vice versa.

There is competition between individual fish species for food. If there are predatory fish in the reservoir, peaceful and smaller fish serve as food for them. With an excessive increase in the number of predatory fish, the number of fish that serve as food for them decreases and, at the same time, the breed quality of predatory fish deteriorates, they are forced to switch to cannibalism, that is, they eat individuals of their own species and even their descendants.

The nutrition of fish is different, depending on their type, age, and also the time of year.

stern fish are planktonic and benthic organisms.

Plankton from the Greek planktos - soaring - is a collection of plant and animal organisms that live in water. They are completely devoid of organs of movement, or have weak organs of movement that cannot resist the movement of water. Plankton is divided into three groups: zooplankton - animal organisms represented by various invertebrates; phytoplankton are plant organisms represented by a variety of algae, and bacterioplankton occupies a special place (Fig. 4 and 5).

Planktonic organisms tend to be small and have a low density, which helps them float in the water column. Freshwater plankton consists mainly of protozoa, rotifers, cladocerans and copepods, green, blue-green and diatoms. Many of the planktonic organisms are food for juvenile fish, and some are also eaten by adult planktivorous fish. Zooplankton has high nutritional qualities. So, in daphnia, the dry matter of the body contains 58% protein and 6.5% fat, and in cyclops - 66.8% protein and 19.8% fat.

The population of the bottom of the reservoir is called benthos, from the Greek benthos- depth (Fig. 6 and 7). Benthic organisms are represented by diverse and numerous plants (phytobenthos) and animals (zoobenthos).

By nature of food fish of inland waters are divided into:

1. Herbivores that eat mainly aquatic flora (grass carp, silver carp, roach, rudd, etc.).

2. Animal eaters that eat invertebrates (roach, bream, whitefish, etc.). They are divided into two subgroups:

planktophages that feed on protozoa, diatoms and some algae (phytoplankton), some coelenterates, molluscs, eggs and larvae of invertebrates, etc.;

benthophages that feed on organisms that live on the ground and in the soil of the bottom of reservoirs.

3. Ichthyophages, or carnivores that feed on fish, vertebrates (frogs, waterfowl, etc.).

However, this division is conditional.

Many fish have a mixed diet. For example, carp is omnivorous, eating both plant and animal food.

The fish are different according to the nature of the laying of eggs during the spawning period. The following ecological groups are distinguished here;

lithophiles- breed on rocky ground, usually in rivers, on the current (sturgeon, salmon, etc.);

phytophiles- breed among plants, lay eggs on vegetative or dead plants (carp, carp, bream, pike, etc.);

psammophiles- lay eggs on the sand, sometimes attaching it to the roots of plants (peled, vendace, gudgeon, etc.);

pelagophiles- they spawn into the water column, where it develops (amour, silver carp, herring, etc.);

ostracophiles- lay eggs inside

the mantle cavity of molluscs and sometimes under the shells of crabs and other animals (mustards).

Fish are in a complex relationship with each other, life and their growth depend on the state of water bodies, on biological and biochemical processes occurring in the water. For artificial breeding of fish in reservoirs and for the organization of commercial fish farming, it is necessary to study well the existing reservoirs and ponds, to know the biology of fish. Fish-breeding activities carried out without knowledge of the matter can only cause harm. Therefore, fishery enterprises, state farms, collective farms should have experienced fish farmers and ichthyologists.