Anisimova I.M., Lavrovsky V.V. Ichthyology. Structure and some physiological characteristics of fish. Excretory system and osmoregulation. Migratory fishes What physiological characteristics of migratory fishes allow them

Optimal development temperatures can be determined by assessing the intensity of metabolic processes at individual stages (with strict morphological control) by changes in oxygen consumption as an indicator of the rate of metabolic reactions during different temperatures. The minimum oxygen consumption for a certain stage of development will correspond to the optimal temperature.

Factors influencing the incubation process and the possibilities of their regulation.

Of all the abiotic factors, the most powerful in its effect on fish is temperature. Temperature has a very large influence on the embryogenesis of fish at all stages and stages of embryo development. Moreover, for each stage of embryo development there is an optimal temperature. Optimal temperatures are defined as: at which the highest rate of metabolism (metabolism) is observed at certain stages without disrupting morphogenesis. The temperature conditions under which embryonic development takes place in natural conditions and with existing methods of egg incubation almost never correspond to the maximum manifestation of valuable species characteristics of fish useful (needed) to humans.

Methods for determining optimal temperature conditions for development in fish embryos are quite complex.

It has been established that during the development process, the optimal temperature for spring-spawning fish increases, and for autumn-spawning fish it decreases.

The size of the optimal temperature zone expands as the embryo develops and reaches its largest size before hatching.

Determining the optimal temperature conditions for development allows not only to improve the incubation technique (keeping pre-larvae, rearing larvae and rearing juveniles), but also opens up the possibility of developing techniques and methods for directed influence on development processes, obtaining embryos with given morphofunctional properties and given sizes.

Let us consider the impact of other abiotic factors on egg incubation.

The development of fish embryos occurs with constant consumption of oxygen from the external environment and the release of carbon dioxide. A constant product of embryo excretion is ammonia, which arises in the body during the breakdown of proteins.

Oxygen. The ranges of oxygen concentrations within which the development of embryos of different fish species is possible vary significantly, and the oxygen concentrations corresponding to the upper limits of these ranges are much higher than those found in nature. Thus, for pike perch, the minimum and maximum oxygen concentrations at which embryo development and prelarval hatching still occur are 2.0 and 42.2 mg/l, respectively.

It has been established that with an increase in oxygen content in the range from the lower lethal limit to values ​​significantly exceeding its natural content, the rate of embryo development naturally increases.

Under conditions of insufficient or excess oxygen concentrations, embryos exhibit large differences in the nature of morphofunctional changes. Thus, at low oxygen concentrations the most typical anomalies are expressed in body deformation and disproportionate development and even absence of individual organs, the appearance of hemorrhages in the area of ​​large vessels, the formation of dropsy on the body and gall sac. At elevated oxygen concentrations the most characteristic morphological disorder in embryos is a sharp weakening or even complete suppression of erythrocyte hematopoiesis. Thus, in pike embryos that developed at an oxygen concentration of 42-45 mg/l, by the end of embryogenesis, red blood cells in the bloodstream completely disappear.

Along with the absence of red blood cells, other significant defects are observed: muscle motility ceases, the ability to respond to external irritations and to free itself from membranes is lost.

In general, embryos incubated at different oxygen concentrations differ significantly in the degree of their development at hatching

Carbon dioxide (CO). Embryo development is possible in a very wide range of CO concentrations, and the concentration values ​​corresponding to the upper limits of these ranges are much higher than those that embryos encounter under natural conditions. But with an excess of carbon dioxide in the water, the number of normally developing embryos decreases. In experiments it was proven that an increase in the concentration of dioxide in water from 6.5 to 203.0 mg/l causes a decrease in the survival rate of chum salmon embryos from 86% to 2%, and with a carbon dioxide concentration of up to 243 mg/l - all embryos during incubation died.

It has also been established that embryos of bream and other species of cyprinids (roach, blue bream, silver bream) develop normally at a carbon dioxide concentration in the range of 5.2-5.7 mg/l, but when its concentration increases to 12.1-15.4 mg /l and decreasing the concentration to 2.3-2.8 mg/l, increased mortality of these fish was observed.

Thus, both a decrease and an increase in the concentration of carbon dioxide has a negative effect on the development of fish embryos, which gives grounds to consider carbon dioxide a necessary component of development. The role of carbon dioxide in fish embryogenesis is diverse. An increase in its concentrations (within normal limits) in water enhances muscle motility and its presence in the environment is necessary to maintain the level of motor activity of embryos; with its help, the oxyhemoglobin of the embryo breaks down and thereby ensures the necessary tension in the tissues; it is necessary for the formation of organic compounds of the body.

Ammonia in bony fishes it is the main product of nitrogen excretion both during embryogenesis and in adulthood. In water, ammonia exists in two forms: in the form of undissociated (not separated) NH molecules and in the form of ammonium ions NH. The ratio between the amount of these forms depends significantly on temperature and pH. With increasing temperature and pH, the amount of NH increases sharply. The toxic effect on fish is predominantly caused by NH. The effect of NH has a negative effect on fish embryos. For example, in trout and salmon embryos, ammonia causes a disruption in their development: a cavity filled with a bluish liquid appears around the yolk sac, hemorrhages form in the head section, and motor activity decreases.

Ammonium ions at a concentration of 3.0 mg/l cause a slowdown in linear growth and an increase in body weight of pink salmon embryos. At the same time, it must be borne in mind that ammonia in bony fish can be included secondarily in metabolic reactions and form non-toxic products.

Hydrogen indicator pH of water, in which embryos develop should be close to the neutral level - 6.5-7.5.

Water requirements. Before supplying water to the incubation apparatus, it must be purified and neutralized using settling tanks, coarse and fine filters, and bactericidal installations. The development of embryos can be negatively affected by the brass mesh used in incubation apparatus, as well as fresh wood. This influence is especially pronounced if sufficient flow is not ensured. Exposure to brass mesh (more precisely, copper and zinc ions) inhibits growth and development and reduces the vitality of embryos. Exposure to substances extracted from wood leads to dropsy and abnormalities in the development of various organs.

Water flow. For normal development of embryos, water flow is necessary. The absence of flow or its insufficiency has the same effect on embryos as a lack of oxygen and an excess of carbon dioxide. If there is no water change at the surface of the embryos, then the diffusion of oxygen and carbon dioxide through the membrane does not provide the necessary intensity of gas exchange and the embryos experience a lack of oxygen. Despite the normal saturation of water in the incubation apparatus. The efficiency of water exchange depends to a greater extent on the circulation of water around each egg than on the total amount of incoming water and its speed in the incubation apparatus. Effective water exchange during incubation of eggs in a stationary state (salmon eggs) is created by circulating water perpendicular to the plane of the frames with eggs - from bottom to top with an intensity in the range of 0.6-1.6 cm/sec. This condition is fully met by the IM incubation apparatus, which imitates the conditions of water exchange in natural spawning nests.

For the incubation of beluga and stellate sturgeon embryos, water consumption is considered optimal in the range of 100-500 and 50-250 ml per embryo per day, respectively. Before the hatching of prelarvae, the water flow in the incubation apparatus is increased in order to ensure normal conditions for gas exchange and remove metabolic products.

It is known that low salinity (3-7) is detrimental to pathogenic bacteria and fungi and has a beneficial effect on the development and growth of fish. In water with a salinity of 6-7, not only the waste of developing normal embryos is reduced and the growth of juveniles is accelerated, but also overripe eggs develop, which die in fresh water. An increased resistance of embryos developing in brackish water to mechanical stress was also noted. Therefore in Lately The question of the possibility of growing anadromous fish in brackish water from the very beginning of their development becomes of great importance.

The influence of light. When carrying out incubation, it is necessary to take into account the adaptability of embryos and prelarvae of various fish species to lighting. For example, light is harmful to salmon embryos, so incubation apparatus must be darkened. Incubation of sturgeon caviar in complete darkness, on the contrary, leads to developmental delays. Impact of direct sunlight causes inhibition of the growth and development of sturgeon embryos and a decrease in the viability of prelarvae. This is due to the fact that sturgeon caviar naturally develops in turbid water and at a considerable depth, that is, in low light. Therefore, during artificial reproduction of sturgeon, incubation apparatus should be protected from direct sunlight, as it can cause damage to the embryos and the appearance of malformations.

Caring for eggs during incubation.

Before starting the fish-breeding cycle, all incubation devices must be repaired and disinfected with a bleach solution, rinsed with water, and the walls and floors washed with 10% lime solution (milk). For preventive purposes, eggs should be treated with a 0.5% formaldehyde solution for 30-60 seconds before being loaded into incubation apparatuses against saprolegnia damage to eggs.

Caring for eggs during the incubation period consists of monitoring temperature, oxygen concentration, carbon dioxide, pH, flow, water level, light conditions, and the condition of the embryos; selection of dead embryos (with special tweezers, screens, pears, siphon); preventive treatment as needed. Dead eggs are whitish in color. When salmon eggs become silted, showering is carried out. Smothering and collection of dead embryos should be carried out during periods of decreased sensitivity.

Duration and characteristics of incubation of eggs of various fish species. Hatching of prelarvae in various incubation apparatuses.

The duration of egg incubation largely depends on the water temperature. Usually, with a gradual increase in water temperature within the optimal boundaries for embryogenesis of a particular species, the development of the embryo gradually accelerates, but when approaching the temperature maximum, the development rate increases less and less. At temperatures close to the upper threshold, in the early stages of fragmentation of fertilized eggs, its embryogenesis, despite the increase in temperature, slows down, and with a higher increase, death of the eggs occurs.

Under unfavorable conditions (insufficient flow, overload of incubation apparatus, etc.), the development of incubated eggs slows down, hatching begins late and takes longer. The difference in the duration of development at the same water temperature and different flow rates and loading can reach 1/3 of the incubation period.

Features of incubation of eggs of various fish species. (sturgeon and salmon).

Sturgeon: supplying incubators with water with oxygen saturation 100%, carbon dioxide concentration not more than 10 mg/l, pH - 6.5-7.5; protection from direct sunlight to avoid damage to embryos and the appearance of malformations.

For stellate sturgeon, the optimal temperature is from 14 to 25 C, at a temperature of 29 C the development of embryos is inhibited, at 12 C there is a great death and many freaks appear.

For the spring beluga, the optimal incubation temperature is 10-15 C (incubation at a temperature of 6-8 C leads to 100% death, and at 17-19 C many abnormal prelarvae appear.)

Salmonids. The optimal oxygen level at the optimal temperature for salmonids is 100% of saturation, the dioxide level is no more than 10 mg/l (for pink salmon no more than 15, chum salmon no more than 20 mg/l), pH - 6.5-7.5; complete darkness during incubation of salmon eggs, protection from direct sunlight for whitefish eggs.

For Baltic salmon, salmon, Ladoga salmon, the optimal temperature is 3-4 C. After hatching, the optimal temperature rises to 5-6, and then to 7-8 C.

Incubation of whitefish eggs mainly occurs at a temperature of 0.1-3 C for 145-205 days, depending on the type and thermal regime.

Hatching. The duration of hatching is not constant and depends not only on temperature, gas exchange, and other incubation conditions, but also on specific conditions (flow speed in the incubation apparatus, shocks, etc.) necessary for the release of the enzyme for hatching embryos from the shells. The worse the conditions, the longer duration hatching.

Usually, under normal environmental conditions, the hatching of viable prelarvae from one batch of caviar is completed in sturgeon within a few hours to 1.5 days, in salmon – 3-5 days. The moment when there are already several dozen prelarvae in the incubation apparatus can be considered the beginning of the hatching period. Usually this is followed by a mass hatching, and at the end of hatching, dead and deformed embryos remain in the shells in the apparatus.

Extended hatching periods most often indicate unfavorable environmental conditions and lead to an increase in the quality of prelarvae and an increase in their mortality. Prolonged hatching is a big inconvenience for the fish farmer, so it is important to know the following.

The hatching of the embryo from the eggs depends largely on the release of the hatching enzyme in the hatching gland. This enzyme appears in the gland after the heart begins to pulsate, then its amount rapidly increases until the last stage of embryogenesis. At this stage, the enzyme is released from the gland into the periviteline fluid, the enzymatic activity of which increases sharply, and the activity of the gland decreases. The strength of the shells quickly decreases with the appearance of the enzyme in the periviteline liquid. Moving in weakened shells, the embryo breaks them, enters the water and becomes a prelarva. The secretion of the hatching enzyme and muscle activity, which are of primary importance for release from the membranes, are largely dependent on external conditions. They are stimulated by improved aeration conditions, water movement, and shocks. To ensure a friendly hatching, for example, in sturgeons, it is necessary: ​​strong flow and vigorous mixing of eggs in the incubation apparatus.

The timing of hatching of prelarvae also depends on the design of the incubation apparatus. Thus, for sturgeons, the most favorable conditions for friendly hatching are created in the “sturgeon” incubator, in Yushchenko’s apparatus the hatching of larvae is significantly extended, and even less favorable conditions for hatching are in the tray incubation apparatus of Sadov and Kahanskaya.

SUBJECT. BIOLOGICAL BASES OF RESISTANCE OF PRELARVALS, GROWING OF LARVAES AND GROWING OF JUVENILE FISH.

The choice of fish farming equipment depending on the ecological and physiological properties of the species.

In the modern technological process of factory fish reproduction, after the incubation of eggs, the incubation of prelarvae, the rearing of larvae and the rearing of juveniles begin. Such technology system provides for complete fish farming control during the formation of the fish organism, when important biological transformations of the developing organism occur. For sturgeon and salmon, for example, such transformations include the formation of an organ system, growth and development, physiological preparation for life in the sea.

In all cases, violations of environmental conditions and breeding technology associated with the lack of correct ideas about certain features of the biology of the bred object or mechanical use fish farming techniques, equipment and regime, without understanding the biological meaning, entail increased mortality of farmed fish during early ontogenesis.

One of the most critical periods of the entire biotechnical process of artificial fish reproduction is the maintenance of prelarvae and the rearing of larvae.

The prelarvae released from the shells undergo a passive state in their development, which is characterized by low mobility. When keeping prelarvae, the adaptive features of this period of development of a given species are taken into account and conditions are created that ensure the greatest survival before switching to active feeding. With the transition to active (exogenous) nutrition, the next link in the fish farming process begins - the rearing of larvae.

pocket field identifiers: , , ,
colored laminated identification tables: , , , ,
clamshell color guide
methodological guide.

PHYSIOLOGY AND ECOLOGY OF FISH

Sense organs are represented on the head of fish eyes and holes olfactory capsules

Almost all fish distinguish colors, and some species can reflexively change your own color: light stimuli are converted by the organs of vision into nerve impulses that reach the pigment cells of the skin.

Fish recognize well smells and availability flavoring agents in water; in many species, taste buds are located not only in the oral cavity and on the lips, but also on various antennae and skin projections around the mouth.

On the head of the fish are seismosensory channels and electrosensitive organs that allow them to navigate in the dark or muddy water based on the slightest changes in the electric field. They make up the sensory system side line. In many species, the lateral line is clearly visible as one or several chains of scales with small holes.

Fish do not have external hearing organs (auditory openings or auricles), but well-developed inner ear allows them to hear sounds.

Breath of fish carried out through rich blood vessels gills(gill filaments), and some species (loaches) have developed adaptations for additional breathing with atmospheric air when there is a deficiency of oxygen in the water (during death, high temperature, etc.). Loaches swallow air, which then enters the blood through the blood vessels and capillaries of the internal organs.

Fish movements very diverse. Fish usually move using wavy body curves.

Fish with a serpentine body shape (lamprey, eel, loach) move with the help of curves of the whole body. Their speed of movement is low (picture on the left):

Body temperature in fish is determined by the temperature of the surrounding water.

In relation to water temperature, fish are divided into cold-loving (cold-water) And thermophilic (warm-water). Some species thrive under the Arctic ice, and some species can freeze in the ice for several months. Tench and crucian carp tolerate freezing of reservoirs to the bottom. A number of species that calmly tolerate freezing of the surface of a reservoir are not able to reproduce if in the summer the water does not warm up to a temperature of 15-20 ° C (catfish, silver carp, carp).

For most cold-water species (whitefish, trout), water temperatures greater than 20° C are unacceptable, since oxygen content V warm water not enough for these fish. It is known that the solubility of gases, including oxygen, in water decreases sharply with increasing temperature. Some species easily tolerate oxygen deficiency in water over a wide range of temperatures (crucian carp, tench), while others live only in cold and oxygen-rich water of mountain rivers (grayling, trout).

Fish coloring can be very diverse. In almost all cases, the color of the fish plays either masking(from predators), or signaling(in gregarious species) role. The color of fish varies depending on the season, living conditions and physiological state; Many fish species are most brightly colored during the breeding season.

There is a concept nuptial coloration(nuptial outfit) of fish. During the breeding season, some species (roach, bream) develop “pearly” tubercles on their scales and scalp.

Fish migrations

Migrations Most fish are associated with changing bodies of water that differ in water salinity.

Towards water salinity All fish can be divided into three groups: maritime(live at salinity close to oceanic), freshwater(cannot tolerate salinity) and brackish water, found both in the estuarine areas of the sea and in the lower reaches of rivers. The latter species are close to the species, feeding in brackish-water deltas, bays and estuaries, and spawning in rivers and floodplain lakes.

Truly freshwater fish are fish that live and reproduce only in fresh water (minnow).

A number of species that usually live in sea or fresh water can easily move to “atypical” water in new conditions. Thus, some gobies and pipefish have spread along the rivers and reservoirs of our southern rivers.

A separate group is formed migratory fish, spending most of their lives in the sea (feeding and maturing, i.e. growing in the sea), and on spawning coming into rivers or, conversely, i.e. making spawning migrations from rivers to seas.

These fish include many commercially valuable sturgeon and salmon fish. Some species of fish (salmon) return to the bodies of water where they were born (this phenomenon is called homing - home instinct). These abilities of salmon are actively used when introducing eggs into rivers that are new to these fish. The mechanisms that allow migratory fish to accurately find their home river or lake are unknown.

There are species that live most of their lives in rivers and go to the sea to spawn (i.e. vice versa). Among our fauna, such journeys are made by the river eel, which lives and matures in rivers and lakes, and goes into the Atlantic Ocean to procreate.

In migratory fish, when moving from one environment to another, it is noticeable metabolism changes(most often when the reproductive products mature, they stop feeding) and appearance (body shape, coloring, etc.). Often these changes are irreversible - many species after spawning die.

On our website you can also get acquainted with general information about Russian fish: introduction, external structure of fish, physiology and ecology of fish, fish farming, protection of fish resources and aquarium husbandry, dictionary of terms in ichthyology, literature on fish of Russia and the USSR.

Structure and physiological characteristics of fish

Contents

Body shape and movement patterns

Fish skin

Digestive system

Respiratory system and gas exchange (New)

Circulatory system

Nervous system and sensory organs

Endocrine glands

Venom content and toxicity of fish

Fish body shape and fish movement patterns

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.
A body shape that meets these requirements has been 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 movement in the desired direction. Up to 12 different types of body shape have been identified according to lifestyle

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

Arrow-shaped - the bones of the snout are elongated and pointed, the body of the fish has the same height along its entire length, the dorsal fin is assigned to the caudal fin and is located above the anal fin, which creates an imitation of the plumage of an arrow. This form is typical for fish that do not move long distances, stay in ambush and develop high speeds movements for a short period of time due to the push of the fins when throwing at prey or avoiding a predator. These are pike (Esox), garfish (Belone), etc. Torpedo-shaped (it is often called spindle-shaped) - characterized by a pointed head, a rounded body that has an oval shape in cross-section, a thin caudal peduncle, often with additional fins. It is characteristic of good swimmers capable of long movements - tuna, salmon, mackerel, sharks, etc. These fish are capable of swimming for a long time, so to speak, at a cruising speed of 18 km per hour. Salmon are capable of making two to three meter jumps when overcoming obstacles during spawning migrations. The maximum speed that fish can develop is 100-130 km per hour. This record belongs to the sailfish. The body is symmetrically compressed laterally - strongly compressed laterally, tall with a relatively short length and tall. These are fish of coral reefs - bristletooths (Chaetodon), thickets of bottom vegetation - angelfish (Pterophyllum). This body shape helps them easily maneuver among obstacles. Some pelagic fish also have a symmetrically laterally compressed body shape, which needs to quickly change their position in space to disorient predators. The sunfish (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 bottom-dwelling, sedentary fish of the order Flounders, helping them to camouflage well on the bottom. The wave-like bending of the long dorsal and anal fins plays an important role in the movement of these fish. The body, flattened in the dorsoventral direction, is strongly compressed in the dorsoventral direction; as a rule, the pectoral fins are well developed. Sedentary bottom fish have this body shape - most stingrays (Batomorpha), monkfish (Lophius piscatorius L.). The flattened body camouflages fish in the bottom conditions, and the eyes located on top help to see prey. Eel-shaped - the body of the fish is elongated, rounded, looking like an oval in cross section. The dorsal and anal fins are long, there are no ventral fins, and the caudal fin is small. It is characteristic of such benthic and demersal fish as eels (Anguilliformes), which move by laterally bending their body. 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. Their movement pattern is the same as that of eel-shaped fish. This body shape is characteristic of the saberfish (Trichiuridae), the herring king (Regalecus). Macro-shaped - the body of the fish is high in the front, narrowing in the back, especially in the tail. The head is large, massive, the eyes are large. Characteristic of deep-sea, sedentary fish - macrurus and chimera-like fish (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 the Ostracion. spherical shape characteristic of some species from the order Tetraodontiformes - ball fish (Sphaeroides), hedgehog fish (Diodon), etc. These fish are poor swimmers and move with the help of undulating (wave-like) movements of their fins over short distances. When in danger, fish inflate the air sacs of their intestines, filling them with water or air; At the same time, the thorns and thorns present on the body are straightened, protecting them from predators. The needle-shaped body shape is characteristic of pipefish (Syngnathus). Their elongated body, hidden in a bony shell, imitates the leaves of zoster, in the thickets of which they live. Fish lack lateral mobility and move using the undulating (wave-like) action of the dorsal fin.
It is not uncommon to encounter fish whose body shape simultaneously resembles different types of shapes. To eliminate the unmasking shadow on the belly of the fish that appears when illuminated from above, small pelagic fish, for example herring (Clupeidae), sabrefish (Pelecus cultratus (L.)], have a pointed, laterally compressed abdomen with a sharp keel. Large mobile pelagic predators have a pointed, laterally compressed abdomen with a sharp keel. mackerel (Scomber), swordfish (Xiphias gladius L.), tuna (Thunnus) - the keel usually does not develop. Their method of defense is speed of movement, and not camouflage. In bottom fish, the cross-sectional shape approaches an isosceles trapezoid facing with a large base downwards, which eliminates the appearance of shadows on the sides when illuminated from above.Therefore, most bottom-dwelling fish have a wide, flattened body.

SKIN, SCALES AND LUMOUS ORGANS

Rice. Shape of fish scales. 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 shed, and new ones appear in their place. Ganoid - mainly in fossil fish. The scales are rhombic in shape, closely articulated with one another, so that the body is enclosed in a shell. Scales do not change over time. The scales get their name from ganoin (a dentin-like substance), which lies in a thick layer on the bone plate. Among modern fish, armored pikes and polyfins have it. In addition, sturgeons have it in the form of plates on the upper lobe of the caudal fin (fulcra) and bugs scattered throughout the body (a modification of several fused ganoid scales).
Gradually changing, the scales lost ganoin. Modern bony fish no longer have it, and the scales consist of bony plates ( bone scale). These scales can be cycloid - rounded, with smooth edges (cyprinids) or ctenoid with a serrated posterior edge (perchs). 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 one individual has scales of both forms.
The size and thickness of fish scales vary greatly - from the microscopic scales of the common eel to the very large, palm-sized scales of the three-meter long barbel living in Indian rivers. Only a few fish do not have scales. In some, it has merged into a solid, motionless shell, like a boxfish, or formed rows of closely connected bony plates, like in 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 layer, so it is darker than the summer one. By the number of summer and winter layers on the scales, the age of some fish can be determined.
Many fish have silvery guanine crystals under their scales. 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, you can observe a number of prominent scales with holes that form the lateral line - one of the most important sensory organs. 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.
Many fish, including cyprinids, produce a so-called fear substance (ichthyopterin), which is released into the water from the body of a wounded individual and is perceived by its relatives as a signal notifying of danger.
Fish skin quickly regenerates. Through it, on the one hand, partial release of the final metabolic products occurs, and on the other, 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.
The integumentary bones of the skull and girdle are formed in the thickness of the corium pectoral fins.
Through the muscle fibers of the myomeres connected to its inner surface, the skin participates in the work of the trunk-caudal 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 the internal organs (visceral).

In the first, the muscles of the torso, head and fins are distinguished. 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 strongly developed. It allows the fish to swim. In real fish, it is represented by two large cords located along the body from head to tail (large lateral muscle - m. lateralis magnus) (Fig. 1). The longitudinal connective tissue layer divides this muscle into dorsal (upper) and abdominal (lower) parts.

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

1 - myomeres, 2 - myosepta

The lateral muscles are divided by myosepta into myomeres, 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, alternately contracting, bend the tail 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 the tail in sturgeons and teleosts lies the direct lateral superficial muscle (m. rectus lateralis, m. lateralis superficialis). Salmon fish store a lot of fat in it. The rectus abdominal muscle (m. rectus abdominalis) stretches along the lower side of the body; Some fish, such as eels, do not have it. Between it and the direct lateral superficial muscle are the oblique muscles (m. obliguus).
Groups of muscles 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.

There are striated muscles (which act 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. The trunk muscles can contract quickly and strongly, but soon become fatigued. The peculiarity 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 functioning of this organ.
Smooth muscles also consist of fibers, but much shorter and not showing transverse striations. These are the muscles of internal organs and the walls of blood vessels that have peripheral (sympathetic) innervation.
Striated fibers, and therefore muscles, are divided into red and white, differing, as the name suggests, in color. The color is due to the presence of myoglobin, a protein that easily binds oxygen. Myoglobin provides respiratory phosphorylation, accompanied by the release of large amounts of energy.
Red and white fibers differ in a number of morphophysiological characteristics: color, shape, mechanical and biochemical properties (respiration rate, glycogen content, etc.).
The fibers of the red muscle (m. lateralis superficialis) are 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;
they contain accumulations of fat and glycogen. Their excitability is less, individual contractions last longer, but proceed more slowly; oxidative, phosphorus and carbohydrate metabolism is more intense than in white ones.
The heart muscle (red) has little glycogen and many enzymes of aerobic metabolism (oxidative metabolism). It is characterized by a moderate rate of contraction and fatigues more slowly than white muscles.
In wide, thicker, lighter white fibers m. lateralis magnus there is little myoglobin, they have less glycogen and respiratory enzymes. Carbohydrate metabolism occurs predominantly anaerobically, and the amount of energy released is less. Individual contractions are fast. Muscles contract and fatigue faster than red muscles. They lie deeper.
The red muscles are constantly active. They ensure long-term and continuous functioning of the organs, support the constant movement of the pectoral fins, ensure the bending of the body during swimming and turning, and the continuous functioning of the heart.
With fast movement and throws, white muscles are active, with slow movements, red muscles. 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 muscle tissue in fish is made up of white muscles. For example, in asp, roach, sabrefish, their share is 96.3; 95.2 and 94.9% respectively.
White and red muscles differ in chemical composition. Red muscle contains more fat, while white muscle contains more moisture and protein.
The thickness (diameter) of 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 carp raised on natural food, the diameter of the muscle fiber is (μm): in fry - 5 ... 19, in fingerlings - 14 ... 41, in two-year-olds - 25 ... 50.
The trunk muscles form the bulk of the meat of the fish. The yield of meat as a percentage of total body weight (meatiness) is not the same in different species, and in individuals of the same species it differs depending on gender, conditions of detention, etc.
Fish meat is digested faster than the meat of warm-blooded animals. It is often colorless (pike 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%), but in different fish there are 4...7 protein fractions.
The chemical composition of meat (water, fats, proteins, minerals) varies not only among 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 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. The muscles are hydrated - the dry matter content is reduced by more than half; Fat and nitrogenous substances practically disappear from the muscles - the fish loses up to 98.4% fat and 57% protein.
Features of the environment (primarily food and water) can greatly change nutritional value fish: in swampy, muddy or oil-polluted waters, 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 tissue, by which one can judge the content of complete muscle proteins in the muscles (compared to defective proteins of the connective tissue layer). This ratio changes depending on the physiological state of the fish and environmental factors. In the muscle proteins of teleost fish, proteins account for: sarcoplasm 20 ... 30%, myofibrils - 60 ... 70, stroma - about 2%.
The entire variety of body movements is ensured by the work of the muscular system. It mainly ensures the release of heat and electricity in the fish’s body. An electric current is generated when a nerve impulse is carried along a nerve, during contraction of myofibrils, irritation of light-sensitive cells, mechanochemoreceptors, etc.
Electric organs

Electrical organs are peculiarly modified 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 (the electric eel has about 6000 of them), transformed into electric plates (electrocytes), interlayered with gelatinous connective tissue. The lower part of the plate is negatively charged, the upper part is positively charged. Discharges occur under the influence of impulses from the medulla oblongata. As a result of discharges, water decomposes into hydrogen and oxygen, therefore, for example, in the frozen reservoirs of the tropics, small inhabitants - mollusks, crustaceans, attracted by more favorable breathing conditions - accumulate near electric fish.
Electrical organs can be located in different parts of the body: for example, in a stingray sea ​​fox- on the tail, for electric catfish - on the sides.
By generating electric current and sensing lines of force,
distorted by objects encountered along the way, fish navigate the stream, detect obstacles or prey from a distance of several meters, even in muddy water.
According to their ability to generate electric fields, fish are divided into three groups:
1. Highly electrical types - have large electrical organs that generate discharges from 20 to 600 and even 1000 V. The main purpose of discharges is attack and defense ( electric eel, electric stingray, electric catfish).
2. Weakly electric species - have small electrical organs that generate discharges with a voltage of less than 17 V. The main purpose of the discharges is location, signaling, orientation (many mormyrids, gymnotids, and some stingrays live in the muddy rivers of Africa).
3. Non-electric species - do not have specialized organs, but have electrical activity. The discharges they generate 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, silverside, perch, etc.).

Digestive system

The digestive tract of real fish is divided into the oral cavity, pharynx, esophagus, stomach, and intestines (small, thick, rectum, ending with the anus). Sharks, rays 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 flow.

There are no salivary glands in the mouth of fish. The glandular cells of the oral cavity and pharynx secrete mucus, which does not have digestive enzymes and only promotes the swallowing 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, inclined inward towards the pharynx and used to grasp and hold the victim. Many peaceful fish (many herrings, carp, etc.) do not have teeth on their jaws.

The feeding mechanism is coordinated with the respiratory mechanism. The 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 the gill rakers.

Rice. 1 Gill rakers of planktivorous (a), benthovorous (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 into the esophagus. Predatory fish do not need to filter out food; their stamens are sparse, low, rough, sharp or hooked: they are involved in holding the prey.

Some benthivorous fish have wide and massive pharyngeal teeth on the posterior gill arch. They are used for grinding food.

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

Not all fish have a stomach. The gastric species include carp, many gobies and some others.

The gastric mucosa contains glandular cells. producing hydrochloric acid and pepsin, which breaks down protein in an acidic environment, and mucus. This is where predatory fish digest the bulk of their food.

The bile duct and pancreatic duct flow into the initial part of the intestine (small intestine). Through them, bile and pancreatic enzymes enter the intestines, under the influence of which proteins are broken down into amino acids, fats into glycerol and fatty acids and the breakdown of polysaccharides into sugars, mainly glucose.

In the intestine, in addition to the breakdown of nutrients, their absorption occurs, most intensely in the posterior region. This is facilitated by the folded structure of its walls, the presence of villous outgrowths in them, penetrated by capillaries and lymphatic vessels, and the presence of cells secreting mucus.

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

Carp, catfish, pike and some other fish do not have pyloric appendages. With the help of pyloric appendages, the absorption 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, particularly carp, the anterior part of the intestine is expanded and resembles the shape of a stomach. However, this is only an external analogy: there are no glands characteristic of the stomach that produce pepsin.

The structure, shape and length of the digestive tract are varied due to the nature of food (food items, their digestibility), and the characteristics of digestion. There is a certain dependence of the length of the digestive tract on the type of food. Thus, the relative length of the intestine (the ratio of the length of the intestine to the length of the body) is 6 ... 15 for herbivores (lumpfish and silver carp), 2 ... 3 for omnivores (crucian carp and carp), and 2 ... 3 for carnivores (pike, pike perch, perch) - 0.6 ... 1.2.

The liver is a large digestive gland, second in size only to the gonads in adult fish. Its mass is 14...25% in sharks, 1...8% of body weight in bony sharks. It is a complex tubular-reticular gland, associated in origin with the intestines. In embryos it is a blind outgrowth.

Bile ducts conduct bile into the gallbladder (only a few species do not have one). Bile, due to its alkaline reaction, neutralizes the acidic reaction of gastric juice. It emulsifies fats and activates lipase, a pancreatic enzyme.

From the digestive tract, all blood flows slowly through the liver. In the liver cells, in addition to the formation of bile, the neutralization of foreign proteins and poisons ingested with food occurs, glycogen is deposited, and in sharks and codfish (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 is a complex alveolar gland, also a derivative of the intestine, and is a compact organ only in sharks and a few other fish. In most fish it is not visually detectable, 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, vein, nerve ending and duct that carries secretions 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 intestines.

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

Thus, the pancreas is an external and internal secretion gland.

From the pouch-like invagination of the dorsal part of the beginning of the intestine, the swim bladder is formed in fish - an organ characteristic only of 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 led to the development of adaptations for using air oxygen. Most fish breathe oxygen dissolved in water, but there are species that are partially adapted to air breathing (lungfish, jumper, snakehead, etc.).

Basic respiratory organs. The main organ for extracting oxygen from water is the gills.

The shape of the gills is varied and depends on the species and mobility: sacs with folds (in fish-like fish), plates, petals, bundles of mucous membranes 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 operculum. The four arches on the outer convex side each have two rows of gill filaments supported by supporting cartilages. The gill filaments are covered with thin folds called petals. Gas exchange occurs in them. The number of petals varies; per 1 mm of gill filament there are:

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

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

1 - cartilaginous rod; 2 - gill arch; 3 - gill filaments; 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 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 come closer together, the pressure in the gill cavity increases, the gill slits open and water is pushed out through them.

Rice. 2 Respiration 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 - the oral (associated with the oral muscles) and the 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 is bound by 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 reacts sensitively to the composition of water: toxicants such as ammonia, nitrites, and CO2 at elevated levels affect the respiratory folds within the first 4 hours of contact.

The adaptations for breathing in fish are remarkable during the embryonic period of development - in embryos and larvae, when the gill apparatus has not yet been formed, but 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 - Cuvier’s ducts, veins of the dorsal and caudal fins, the intestinal vein, a network of capillaries on the yolk sac, head, fin border and gill cover; b) external gills

Rice. 3 Respiratory organs in fish embryos

a - pelagic fish; b - carp; c - loach; 1 - Cuvier's ducts; 2 - inferior tail vein; 3 - network of capillaries; 4 - external gills.

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

Additional respiratory organs. Additional devices that help to endure unfavorable oxygen conditions include aquatic cutaneous respiration, i.e., the use of oxygen dissolved in water using the skin, and air breathing—the use of air using the swim bladder, intestines, or through special accessory organs

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

1. Fish that have adapted to live in conditions of severe oxygen deficiency. These are fish that inhabit well-warmed water bodies with a high content of organic matter, in which there is often a lack of oxygen. In these fish, the share of skin respiration in the 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 greatest importance in respiration are devoid of scales or they are small and do 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 the oxygen is consumed through the skin, and the rest is supplied through the intestines.

2. Fish that experience less oxygen deficiency and are exposed to unfavorable conditions less often. These include sturgeons that live near the bottom, but in running water - sterlet, sturgeon, stellate sturgeon. The intensity of their skin respiration is 9...12%.

3. Fish that do not experience 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, and ruff.

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

Not only the surface of the body, but also the gills are involved in extracting oxygen from the air in a humid atmosphere. Temperature is important here.

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

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

Some fish living in unfavorable conditions have developed adaptations for breathing oxygen in the air. For example, breathing through the intestines. Clusters of capillaries form in the intestinal walls. 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 the oxygen is absorbed from the air. This type of breathing is characteristic of loaches, some catfish and carp fish; its meaning varies among different fish. For example, in loaches under conditions of great lack of oxygen, it is this method of respiration that becomes almost equal to the gill method.

When fish die, they swallow air; the 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 labyrinthine in labyrinthine fish, the epibranchial 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, fish breathe atmospheric oxygen and can stay out of water for several days (tropical slider 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 come to land, the operculum closes tightly and protects the gills from drying out. In the snakehead, the protrusion of the pharynx forms an epibranchial cavity, the mucous membrane of its walls is equipped with a dense network of capillaries. Thanks to the presence of an epibranchial organ, it breathes air and can be found in shallow water at 30 ° C. For normal life, the snakehead, like the slider, needs both oxygen dissolved in water and atmospheric oxygen. However, during wintering in ponds covered with ice, it does not use atmospheric air.

The swim bladder is also designed to use oxygen from the air. It reaches its greatest development as a respiratory organ in lungfish. In them it is cellular and functions like a lung. In this case, a “pulmonary circle” of blood circulation occurs,

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

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

By mastering various bodies of water, fish have adapted to life under different gas regimes. The most demanding of the oxygen content in water are salmon, which require 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; For carp, 1.9...2.5 mg/l is usually sufficient.

Each species has its own oxygen threshold, i.e. 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 carp underyearlings raised 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 oxygen. Crucian carp and rotan are partial anaerobes - they can live for several days without oxygen at all, but at low temperatures. It is believed that the body first uses oxygen from the swim bladder, then glycogen from the liver and muscles. Apparently, fish have special receptors in the anterior part of the dorsal aorta or in the medulla oblongata that sense a drop in oxygen concentration in the blood plasma. The endurance of fish is promoted by a large number of carotenoids in the nerve cells of the brain, which are able to accumulate oxygen and release it when there is a deficiency.

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 maturity of the gonads, and physicochemical environmental factors. As fish grow, the activity of oxidative processes in tissues decreases; maturation of the gonads, on the contrary, causes an increase in oxygen consumption. Oxygen consumption in the body of males is higher than that of females.

In addition to the concentration of oxygen in water, the breathing rhythm is affected by the CO2 content, pH, temperature, etc. For example, at a temperature of 10 ° C and an oxygen content of 4.7 mg/l, trout makes 60... 70 respiratory movements per minute, and at 1. 2 kg/l the respiratory rate increases to 140... 160; carp at 10 °C breathes almost twice as slow 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 oversaturation of water with oxygen has a detrimental effect on fish. Thus, the lethal limit for pike embryos is 400% oxygen saturation of water; at 350...430% saturation, the motor activity of roach embryos is impaired. 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 malformations, 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 occurs not due to excess oxygen, but due to a large amount of nitrogen. For example, in salmon larvae and fry die at 103 ... 104%, fingerlings - 105 ... 113, adult fish - at 118% water saturation with nitrogen.

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

Fish quickly adapt to slight oxygen supersaturation. Their metabolism increases and, as a result, feed consumption increases and the feed ratio decreases, embryo development accelerates, and waste decreases.

For normal respiration of fish, the CO2 content in water is very important. At large quantities Carbon dioxide makes it difficult for fish to breathe because the ability of blood hemoglobin to bind oxygen decreases, oxygen saturation in the blood decreases sharply and the fish suffocates. When the CO2 content 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 circulatory system and a two-chambered heart filled with venous blood (with the exception of lungfishes and lobe-finned fish).

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

The expanded initial section of the abdominal aorta in lower fishes (sharks, rays, sturgeons, lungfishes) forms a contracting arterial cone, and in higher fishes it forms an aortic bulb, the walls of which cannot contract. Valves prevent blood from flowing back.

The blood circulation diagram in its most general form is presented as follows. Venous blood filling the heart, during contractions of the strong muscular ventricle, is directed forward through the bulbus arteriosus along the abdominal aorta and rises to the gills along the afferent branchial arteries. Bony fish have four on each side of the head, corresponding to the number of gill arches. In the gill filaments, blood passes through the capillaries and oxidized, enriched with oxygen, is sent through the efferent vessels (there are also four pairs of them) 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 a head circle, characteristic of bony fish. The carotid arteries branch forward from the roots of the aorta.

From the dorsal aorta there are arteries to the internal organs and muscles. In the caudal region, the aorta becomes the caudal artery. In all organs and tissues, arteries break up into capillaries. The venous capillaries that collect venous blood flow into the vein that carries blood to the heart. The tail vein, starting in the caudal region, enters the body cavity and divides into the portal veins of the kidneys. In the kidneys, the branches of the portal veins form the portal system, and after leaving them, they merge into paired posterior cardinal veins. As a result of the merger of the posterior cardinal veins with the anterior cardinal (jugular), collecting blood from the head, and the subclavian veins, bringing 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, collects in the portal vein of the liver, the branches of which in the liver form the portal system. The hepatic vein, which collects blood from the liver, drains directly into the venous sinus

Rice. 1 Diagram 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 - caudal artery; 16 - tail vein; 17 - portal veins of the kidneys; 18 - posterior cardinal vein; 19 - anterior cardinal vein; 20 - subclavian vein; 21 - Cuvier's duct; 22 - portal vein of the liver; 23 - liver; 24 - hepatic vein; Vessels with venous blood are shown in black, and arterial blood in white.

Like other vertebrates, cyclostomes and fish have so-called accessory hearts that maintain pressure in the blood vessels. Thus, 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 work of the additional heart depends on the frequency of movements of the caudal fin.

In lungfish, an incomplete atrial septum appears. This is accompanied by the emergence of a pulmonary circulation passing through the swim bladder, transformed into a lung.

The heart of fish is much smaller and weaker than the heart of land 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 (skate), 11198.8 (pike), 15998.4 (salmon), while in the carotid artery of a horse it is 20664.6.

The heart rate 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 survive freezing into ice, the heart pulsation stops during this period.

The amount of blood in fish is less than in all other vertebrates (1.1..7.3% of body weight, including in 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 blood upward) and less energy expenditure due to life in an aquatic environment. Water is a hypogravitational environment, i.e. the force of gravity has almost no effect here.

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 the individuals. Fish erythrocytes are larger, and their number in the blood is less than in higher vertebrates, while leukocytes, as a rule, are larger. This is due, on the one hand, to the reduced metabolism of fish, and on the other, to the need to strengthen the protective functions of the blood, since the environment is replete with pathogenic organisms. In 1 mm 3 of blood the number of red blood cells 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/mm3. Fish leukocytes are highly diverse. Most species have 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, they are found in cyprinids, Amur herbivores and some perch fish.

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

The number of white blood cells varies greatly throughout the year:

in carp it increases in summer and decreases in winter during starvation due to a decrease in metabolic rate.

A variety of shapes, sizes and numbers 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, dissolved oxygen is carried by the plasma. Thus, in representatives of the family Chaenichthyidae (from the suborder Nototheniaceae), living in the Antarctic seas in low temperature conditions (

The amount of hemoglobin in the body of fish is significantly 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 sturgeon: 4 g/kg in anadromous sturgeon, 0.5 g/kg in burbot. 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 (carp raised on natural food and additional feed have different quantities hemoglobin). The growth rate of fish depends on the amount of hemoglobin.

Living in an environment with little 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 swimmers (mackerel, cod, trout) have a lot of hemoglobin in their blood, and they are very demanding on the oxygen content in the water. Many marine bottom fish, as well as eel, carp, crucian carp and some others, on the contrary, have little hemoglobin in the blood, but it can take oxygen from the environment even with a small amount.

For example, to saturate the blood with oxygen (at 16 °C), pike perch requires a water content of 2.1...2.3 O2 mg/l; If there is 0.56...0.6 mg/l O2 in the water, the blood begins to release it, breathing becomes impossible, and the fish dies. For bream at the same temperature, the presence of 1.0...1.06 mg of oxygen per liter of water is enough to completely saturate hemoglobin with oxygen.

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 up decreases.

Reduces the ability of hemoglobin to take up oxygen and carbon dioxide: in order for the saturation of the eel’s blood with oxygen to reach 50% when the water contains 1% CO2, an oxygen pressure of 666.6 Pa is required, and in the absence of CO2, an oxygen pressure of almost half that is sufficient - 266. 6.„399.9 Pa,

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

Blood, being the internal medium of the body, performs the most important functions: it transports proteins, carbohydrates (glycogen, glucose, etc.) and others. nutrients, playing a large role in energy and plastic metabolism; respiratory—transportation of oxygen to tissues and carbon dioxide to the respiratory organs; excretory—removal of metabolic end products to the excretory organs; regulatory—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, and leukocytes circulating in it have 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 allows its indicators to be used to assess the physiological state.

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

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

1. The formation of blood cells occurs in many organs. The foci of hematopoiesis are: the 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 the tubules), spleen, vascular blood, lymphoid organ ( accumulations of hematopoietic tissue - reticular syncytium - under the roof of the skull). The prints of these organs show blood cells at different stages of development.

2. In bony fishes, hematopoiesis most actively occurs in the lymphoid organs, kidney and spleen, and the main organ of hematopoiesis is the kidneys, namely their anterior part. In the kidneys and spleen, both the formation of red blood cells, white blood cells, platelets, and the breakdown of red blood cells occur.

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

4. Red blood cells 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 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 reduced metabolism, 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. When there is a lack of oxygen, water pollution, transportation and sorting of fish, and 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 and water metabolism in the body depend 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 baroreceptors in 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 along them is discharged to the terminal sections of the veins, in particular to the Cuvier ducts. Some fish have lymphatic hearts.

NERVOUS SYSTEM AND SENSE ORGANS

Nervous system. In fish, it is represented by the central nervous system and the associated peripheral and autonomic (sympathetic) nervous system.
The central nervous system consists of the brain and spinal cord. The peripheral nervous system includes the nerves that extend from the brain and spinal cord to the organs. The autonomic nervous system is based on numerous ganglia and nerves that innervate 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: the part of it lying above the spine and protected by the upper arches of the vertebrae forms the spinal cord, and the extended anterior part, surrounded by a cartilaginous or bone skull, constitutes 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 forebrain, 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, thanks 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, catfishes, cod).
There are no nerve cells in the roof of the forebrain. Gray matter in the form of striatum 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. cells of the olfactory capsule.
The forebrain is the center for processing information coming from the olfactory organs. Thanks 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 to perform such acts as spawning, egg guarding, school formation, aggression, etc.
The optic thalamus are developed in the diencephalon. The optic nerves depart from them, forming a chiasma (crossover, i.e., part of the fibers of the right nerve passes into the left nerve and vice versa). On the lower side of the diencephalon, or hypothalamus, there is a funnel to which the pituitary gland, or pituitary gland, is adjacent; in the upper part of the diencephalon the epiphysis, or pineal gland, develops. The pituitary gland and pineal gland are endocrine glands.
The diencephalon performs numerous functions. It perceives irritations from the retina of the eye, participates in the coordination of movements, and the processing of information from other senses. The pituitary gland and pineal gland carry out hormonal regulation of metabolic processes.
The midbrain is the largest in volume. It has the appearance of two hemispheres, which are called the optic lobes. These lobes are the primary visual centers that perceive stimulation. The fibers of the optic nerve originate from them.
The midbrain processes signals from the organs of vision and balance; Here are located the centers of communication with the cerebellum, medulla oblongata and spinal cord, regulation of color and taste.
The cerebellum is located in the back of the brain and can take the form of either a small tubercle adjacent to the midbrain at the back, or a large sac-like elongated formation adjacent to the medulla oblongata on top. The cerebellum in catfishes reaches especially great development, and in Mormyrus it is the largest among all vertebrates. The cerebellum of fish contains Purkinje cells.
The cerebellum is the center of all motor innervations for swimming and grasping food. It “ensures coordination of movements, maintaining balance, muscle activity, is associated with receptors of the lateral line organs, directs and coordinates the activity of other parts of the brain. When 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 section of the brain, the medulla oblongata, passes into the spinal cord without a sharp boundary. Cavity of the medulla oblongata - the fourth ventricle continues into the cavity
spinal cord is a neurocoel. A significant mass of the medulla consists of white matter.
The majority (six out of ten) of the cranial nerves arise from the medulla oblongata. It is the center for regulating the activity of the spinal cord and the autonomic nervous system. It contains the most important vital centers that regulate the activities 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, the fish quickly dies.
Through the spinal fibers entering the medulla oblongata, the medulla oblongata and spinal cord are connected.
10 pairs of cranial nerves depart from the brain: 1—the olfactory nerve (nervus olfactorius) from the sensory epithelium of the olfactory capsule delivers stimuli to the olfactory bulbs of the forebrain; 2—optic nerve (n. opticus) stretches to the retina from the visual thalamus of the diencephalon; 3—oculomotor nerve (n. oculomotorius) innervates the muscles of the eye, departing 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. glossopharyngeus) goes from the medulla oblongata to the pharynx, innervates the mucous membrane of the pharynx and the muscles of the first branchial arch; 10—vagus nerve (n. vagus) - the longest, connects the medulla oblongata with the branchial apparatus, intestinal tract, heart, swim bladder, lateral line.
The degree of development of different parts of the brain varies among different groups fish and is associated with lifestyle.
The forebrain and olfactory lobes are better developed in cartilaginous fish (sharks and rays) and worse in bony fish. In sedentary fish, such as bottom fish (flounder), the cerebellum is small, but the anterior and medulla oblongata of the brain are more developed in accordance with big role sense of smell and touch in their lives. In well-swimming fish (pelagic, plankton-eating, and predatory), the midbrain (optic lobes) and cerebellum (due to the need for rapid coordination of movement) are more developed. Fish that live in turbid waters have small optic lobes and a small cerebellum. The optic lobes are poorly developed in deep-sea fish. The electrical activity of different parts of the brain is also different: in goldfish, electrical waves in the cerebellum occur 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 located on the inside, and white matter is located on the outside.
The function of the spinal cord is reflexive and conductive. It contains vasomotor centers, trunk muscles, chromatophores, and electrical organs. From the spinal cord metamerically, i.e., corresponding to each vertebra, spinal nerves depart, innervating the surface of the body, the trunk muscles, and, due to the connection of the spinal nerves with the ganglia of the sympathetic nervous system, internal organs. The spinal cord of bony fish contains a secretory organ, the urohypophysis, the cells of which produce a hormone involved in water metabolism.
The autonomic nervous system in cartilaginous fish is represented by disconnected ganglia lying along the spine. Ganglion cells with their processes contact 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 nervous system. The interconnections between 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 internal organs, even if its connection with the central nervous system is disrupted.
The reaction of the fish's body 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. Thus, aquarium and pond fish, soon after the start of regular feeding, accumulate at certain times at the feeders. They also get used to sounds during feeding (tapping on the walls of the aquarium, ringing of 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 form faster in fish 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 out after 28...78 unreinforced signals.
Behavioral reactions are developed in fish faster in a Group (imitation, following the leader in a school, reacting to a predator, etc.). Temporary memory and training are of great importance in fish farming practice. If fish are not taught defensive reactions and communication skills with predators, then juveniles released from fish hatcheries quickly die in natural conditions.
The environmental perception organs (sensory 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 irritations of both physical and chemical nature: pressure, sound, color, temperature, electric and magnetic fields, smell, taste. Some irritations are perceived as a result of direct touch (touch, taste), others are perceived at a distance.
Organs that perceive chemical, tactile (touch), electromagnetic, temperature and other stimuli have a simple structure. Irritations are picked up 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.
Due to the peculiarities living environment In fish, chemical sense systems are of great importance. Chemical irritations are perceived through the sense of smell (sense 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 another sex, avoid enemies, navigate the flow, and defend territory.
Olfactory organs. In fish, like other vertebrates, they are located in the front part of the head and are represented by paired olfactory (nasal) sacs (capsules), opening outwards - the 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 equipped with cilia, and the base is connected to the endings of the olfactory nerve. Receptor surface
organ is large: in the first quarter. mm. Phoxinus has 95,000 receptor cells in the olfactory epithelium. The olfactory epithelium contains numerous cells that secrete mucus.
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 openings. Water penetrates into the anterior cavity, washes the cavity and exits through the posterior opening, washing and irritating the hairs of the receptors.
Under the influence of odorous substances, complex processes occur in the olfactory epithelium: the movement of lipids, protein-mucopolysaccharide complexes and acid phosphatase. The electrical activity of the olfactory epithelium in response to different odorants is different.
The size of the nostrils is related to the lifestyle of the fish: in active fish they are small, since during fast swimming the water in the olfactory cavity is quickly renewed; In sedentary fish, the nostrils are large; they allow a larger volume of water to pass 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, that is, their thresholds of olfactory sensitivity are very low. This especially applies to nocturnal and twilight fish, as well as those living in turbid waters, for which vision helps little in finding food and communicating with relatives.
The sense of smell is most sensitive in migratory fish. Far Eastern salmon accurately find their way from their feeding grounds in the sea to their spawning grounds in the upper reaches of rivers, where they hatched several years ago. At the same time, they overcome enormous distances and obstacles—currents, rapids, rifts. However, the fish correctly find their way only if the nostrils are open, and if they are filled with cotton wool or Vaseline, then the fish walk randomly. It is believed that salmon at the beginning of migration are guided by the sun and stars and, approximately 800 km from their native river, accurately determine their path thanks to chemoreception.
In experiments, when the nasal cavity of these fish was washed away with water from their native spawning ground, a strong electrical reaction occurred 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 other spawning grounds.
Juvenile sockeye salmon can distinguish, with the help of the cells of the olfactory bulb, the water of different lakes, solutions of various amino acids in 10"4 dilution, as well as the concentration of calcium in water. No less striking is the similar ability of the European
eels migrating from Europe to spawning grounds 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 pick up 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 capable of perceiving 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 intertwined with the 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 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 throughout the surface of the body, including the tail.
Catfish perceive taste mainly with the help of their whiskers, since taste buds are concentrated in their epidermis. The number of these buds increases as the fish's body size increases.
Pisces 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, the cave fish Anoptichtys, being blind, sense a glucose solution at a concentration of 0.005%. Fish recognize changes in salinity up to O.Z^/oo, pH—0.05...0.007, carbon dioxide—0.5 g/l, NaCI—0.001...0.005 mole (cyprinids), and minnows—even 0.00004 begging.
Sense organs of the lateral line. A specific organ, characteristic only of fish and amphibians living in 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 carp larvae. Sensing cells (mechanoreceptors) lie among clusters of ectodermal cells on the surface of the skin or in small pits. At the base they are entwined with the terminal branches of the vagus nerve, and in the area rising 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. Branches of the lateral line are also present on the head.

At the bottom of the canal there are groups of sensory cells with cilia. Each such group of receptor cells, together with the nerve fibers in contact with them, forms the organ itself—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 can be complete, that is, stretch along the entire length of the body, or incomplete and even absent, but in the latter case the head canals are strongly developed, as, for example, in herrings.
With the lateral line, the fish senses changes in the pressure of flowing water, low-frequency vibrations (oscillations), 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 the moving flow, but it does not perceive changes in pressure when diving to depth. By catching fluctuations in the water column, the fish detects surface waves, currents, and underwater stationary (rocks, reefs) and moving (enemies, prey) objects.
The lateral line is a very sensitive organ: the shark detects the movement of fish at a distance of 300 m, and migratory fish sense even minor currents of fresh water in the sea.
The ability to catch waves reflected from living and non-living objects is very important for deep-sea fish, since in the darkness of great depths normal visual perception is impossible.
It is assumed that during mating games, fish perceive the lateral line 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 found in the integument of the head and antennae, to which nerve endings are suitable, but they are of much less importance.
Organs of touch. They are clusters of sensory cells (tactile bodies) scattered over the surface of the body. They perceive the touch of hard objects (tactile sensations), water pressure, temperature changes and pain.
There are especially many sensory skin buds in the mouth and 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 pelvic fin, in the trigla (guinea cock) the sense of touch is associated with the rays of the pectoral fins, which feel the bottom. In inhabitants of turbid waters or bottom fish, which are most active at night, the largest number of sensory buds are concentrated on the antennae and fins. In males, the whiskers serve as taste receptors.
Fish seem to feel mechanical injury and pain less strongly than other vertebrates. Thus, sharks that attack prey do not react to blows to the head with a sharp object.
Thermoreceptors. They are the free endings of sensory nerves located in the surface layers of the skin, with the help of which fish perceive water temperature. There are receptors that perceive heat (thermal) and cold (cold). Points of heat perception are found, for example, on the pike’s head, and cold perception points are found on the surface of the body. Bony fish detect temperature changes of 0.1...0.4 degrees. Trout can develop a conditioned reflex to very small (less than 0.1 degrees) and rapid changes in temperature.
The lateral line and brain are very sensitive to temperature. Temperature-sensitive neurons similar to neurons in the thermoregulatory centers of mammals have been found in the fish brain. In trout, the diencephalon contains neurons that respond to increases and decreases in temperature.
Electric sense organs. The organs for sensing electric and magnetic fields are located in the skin over the entire surface of the fish’s body, but mainly in different parts of the head and around it. They are similar to the lateral line organs:
these are pits filled with a mucous mass that conducts current well; at the bottom of the pits there are sensory cells (electroreceptors) 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. The information received by the electroreceptors is analyzed by a 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 senses a current 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 Earth’s electromagnetic field allows
It allows fish to detect the approach of an earthquake 6...24 hours before the start within a radius of up to 2 thousand km.
Organs of vision. They are constructed essentially the same as those of other vertebrates. Their mechanism for perceiving visual sensations is also similar to other vertebrates: light passes into the eye through the transparent cornea, then the pupil (hole in the iris) transmits it to the lens, and the lens transmits (focuses) the light to the inner wall of the eye (retina), where its direct perception occurs (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. Their processes, which are shaped like rods and cones, contain a light-sensitive pigment. The number of these photoreceptor cells is very large: there are 50 thousand of them per 1 mm 2 of the retina in a carp, 162 thousand in a squid, 16 in a spider, and 400 thousand in a human. Through a complex system of contacts between the terminal branches of sensory cells and the dendrites of nerve cells, light stimuli enter the optic nerve.
In bright light, cones perceive the details of objects and color: they capture long wavelengths of the spectrum. Rods perceive weak light, but cannot create a detailed image: when they perceive short waves, they are about 1000 times more sensitive than cones.
The position and interaction of pigment membrane cells, rods and cones changes depending on the light level. In the light, pigment cells expand and cover the rods located near them; The cones are pulled towards the cell nuclei and thus move towards the light. In the dark, sticks are pulled towards the nuclei and are closer to the surface; The cones approach the pigment layer, and the pigment cells that contract in the dark cover them.
The number of different types of receptors depends on the lifestyle of the fish. In diurnal fish, cones predominate in the retina, while in crepuscular and nocturnal fish, rods predominate: burbot has 14 times more rods than pike. Deep-sea fish that live in the darkness of the depths do not have cones, but the rods become larger and their number increases sharply—up to 25 million per 1 mm 2 of the retina; the likelihood of catching even weak light increases. Most fish distinguish colors. Some features in the structure of fish eyes are associated with the characteristics of life in water. They are ellipsoidal in shape and have a silvery shell between the vascular and the albumen, rich in guanine crystals, which gives the eye a greenish-golden sheen. Cornea
fish is almost flat (and not convex), the lens is spherical (and not biconvex)—this expands the field of view. The hole in the iris (pupil) can change its diameter only within small limits. Fish, as a rule, do not have eyelids. Only sharks have a nictitating membrane that covers the eye like a curtain, and some herring and mullet have an adipose eyelid, a transparent film that covers part of the eye.
The location of the eyes on the sides of the head in most species is the reason that fish have primarily monocular vision and limited binocular vision. The spherical shape of the lens and its movement forward to the cornea provides a wide field of vision: light enters the eye from all sides. The vertical viewing angle is 150°, horizontal - 168...170°. But at the same time, the spherical shape of the lens causes myopia in fish. Their range of vision is limited and varies due to the turbidity of the water from several centimeters to several tens of meters. Long-distance vision becomes possible due to the fact that the lens can be pulled back by a special muscle, the falciform process, extending from the choroid of the fundus of the optic cup, and not due to changes in the curvature of the lens, as in mammals.
With the help of vision, fish also orient themselves relative to objects on the ground.
Improved vision in the dark is achieved by the presence of a reflective layer (tapetum) - guanine crystals, underlying pigment. This layer transmits light to the tissues lying behind the retina, but reflects it and returns it again
on the retina. This increases the ability of the receptors to use the light entering the eye.
Due to the living conditions, the eyes of fish can change greatly. In cave or abyssal (deep-sea) forms, the eyes can be reduced and even disappear. Some deep-sea fish, on the contrary, have huge eyes that allow them to capture very weak light, or telescopic eyes, the collecting lenses of which the fish can place parallel and gain binocular vision. The eyes of some eels and larvae of tropical fish are carried forward on long projections (stalked eyes). The modification of the eyes of the four-eyed fish, which lives in the waters of Central and South America, is unusual. Her eyes are placed on the 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 fish sees in the water. The eyes of fish crawling onto land can function in the air.
In addition to the eyes, the pineal gland (endocrine gland) and light-sensitive cells located in the tail, for example, in lampreys, perceive light.
The role of vision as a source of information for most fish is great: during orientation during movement, searching for and capturing food, preserving the school, during the spawning period (perception of defensive and aggressive poses and movements by male rivals, and between individuals of different sexes - mating plumage and spawning “ceremonial”), in the relationship between prey and predator, etc. Carp sees at an illumination level of 0.0001 lux, crucian carp - 0.01 lux.
The ability of fish to perceive light has long been used in fishing: catching fish using light.
It is known that fish of different species react differently to light of different intensities and different wavelengths, i.e., different colors. Thus, bright artificial light attracts some fish (Caspian sprat, saury, horse mackerel, mackerel) and repels others (mullet, lamprey, eel). Different species are also selective in their response to different colors and different light sources—overwater and underwater. All this forms the basis for organizing industrial fishing using electric light. This is how they catch sprat, saury and other fish.
Organ of hearing and balance in fish. It is located at the back of the skull and is represented by a labyrinth. There are no ear openings, pinna and cochlea, i.e. the organ of hearing is represented by the inner ear.
It reaches its greatest complexity in real fish:
The large membranous labyrinth is placed in a cartilaginous or bone chamber under the cover of the ear bones. It has an upper part - an oval sac (ear, utriculus) and a lower part - a round sac (sacculus). From the top. three semicircular canals extend from parts in mutually perpendicular directions, each of which is expanded into an ampulla at one end

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

Endocrine glands

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

Venom content and toxicity of fish

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

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

These fish are harmless when eaten.

Fish, the tissues and organs of which are poisonous in chemical composition, are classified as poisonous and should not be eaten. They are especially numerous in the tropics. The shark Carcharinus glaucus has a poisonous liver, and the shark Tetradon has poisonous ovaries and eggs. In our fauna, the caviar and peritoneum of the marinka Schizothorax and the osman Diptychus are poisonous; in the longhorned beetle Barbus and the khramuli Varicorhynus, the caviar has a laxative effect. I 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 appear when injecting the blood serum of these fish; they disappear when heated, under the influence of acids and alkalis.

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

Peculiarities of life of migratory fish (part 1)

Migrations of pelagic and bottom fish take place in a more or less homogeneous sea environment. Fish only have to adapt somewhat to pressure differences, to different temperatures and minor changes in water salinity, but you do not have to find yourself in a completely new environment, which would require a complete restructuring of the entire physiological side of life. This is not at all what we see during the migrations of migratory fish, which rise from the sea to rivers to reproduce and reach the upper reaches of the latter. They are forced to adapt to an environment that is normally fatal for marine fish. Experiments carried out by Sumner (1906) on a number of marine fish showed that transferring them from sea water to fresh water causes their death, often in a very short time. The cause of death is a change in the osmotic pressure of blood and cavity fluid due to the extraction of the surrounding fresh water salts from the body of the fish. The gills are primarily to blame for this: their thin shells cannot resist osmosis and allow salts to pass through.
Because of this, migratory fish, which change their environment at least twice in their lives (in youth they move from fresh water to sea water, in adulthood they make the reverse transition), have to develop a special ability to tolerate a strong decrease in the concentration of salts in the external environment and retain salts in their environment. body; without passing them through the membranes. Green's experiments (Green, 1905), who determined the content of salts in the blood of Chinook salmon (Ortcorhynchus ischawytscha Walb.) by freezing the blood, showed that in fish taken from the sea, the blood freezing point was 0.762°, in fish that had spent some time in the brackish water estuarine space , - 0.737°, and for fish from the spawning grounds in the upper reaches of the river - 0.628°, which indicates a decrease in the concentration of salts in the blood of the fish by only one fifth. We do not know how this ability to only slightly reduce the concentration of salts in body fluids is achieved, but migratory fish have this ability to a high degree.
In addition to a sharp decrease in salt concentration, migratory fish have to adapt to the fast and strong current of rivers that oppose their movement, to completely different conditions of water temperature, to a different content of gases in it, to a different transparency; you have to develop a whole series of new instincts associated with life in the river, with overcoming various obstacles along the way and with avoiding dangers. Absolutely amazing and incomprehensible to us is the guiding instinct, thanks to which migratory fish find not only the same river in which they hatched, but also the same tributary of it and even supposedly the same spawning ground, as at least some observers claim .

PHYSIOLOGY AND ECOLOGY OF FISH

Sense organs are represented on the head of fish eyes and holes olfactory capsules

Almost all fish distinguish colors, and some species can reflexively change your own color: light stimuli are converted by the organs of vision into nerve impulses that reach the pigment cells of the skin.

Fish recognize well smells and availability flavoring agents in water; in many species, taste buds are located not only in the oral cavity and on the lips, but also on various antennae and skin projections around the mouth.

On the head of the fish are seismosensory channels and electrosensitive organs that allow them to navigate in the dark or muddy water based on the slightest changes in the electric field. They make up the sensory system side line. In many species, the lateral line is clearly visible as one or several chains of scales with small holes.

Fish do not have external hearing organs (auditory openings or auricles), but well-developed inner ear allows them to hear sounds.

Breath of fish carried out through rich blood vessels gills(gill filaments), and some species (loaches) have developed adaptations for additional breathing with atmospheric air when there is a deficiency of oxygen in the water (during death, high temperature, etc.). Loaches swallow air, which then enters the blood through the blood vessels and capillaries of the internal organs.

Fish movements very diverse. Fish usually move using wavy body curves.

Fish with a serpentine body shape (lamprey, eel, loach) move with the help of curves of the whole body. Their speed of movement is low (picture on the left):

Body temperature in fish is determined by the temperature of the surrounding water.

In relation to water temperature, fish are divided into cold-loving (cold-water) And thermophilic (warm-water). Some species thrive under the Arctic ice, and some species can freeze in the ice for several months. Tench and crucian carp tolerate freezing of reservoirs to the bottom. A number of species that calmly tolerate freezing of the surface of a reservoir are not able to reproduce if in the summer the water does not warm up to a temperature of 15-20 ° C (catfish, silver carp, carp).

For most cold-water species (whitefish, trout), water temperatures greater than 20° C are unacceptable, since oxygen content in warm water there is not enough for these fish. It is known that the solubility of gases, including oxygen, in water decreases sharply with increasing temperature. Some species easily tolerate oxygen deficiency in water over a wide range of temperatures (crucian carp, tench), while others live only in cold and oxygen-rich water of mountain rivers (grayling, trout).

Fish coloring can be very diverse. In almost all cases, the color of the fish plays either masking(from predators), or signaling(in gregarious species) role. The color of fish varies depending on the season, living conditions and physiological state; Many fish species are most brightly colored during the breeding season.

There is a concept nuptial coloration(nuptial outfit) of fish. During the breeding season, some species (roach, bream) develop “pearly” tubercles on their scales and scalp.

Fish migrations

Migrations Most fish are associated with changing bodies of water that differ in water salinity.

Towards water salinity All fish can be divided into three groups: maritime(live at salinity close to oceanic), freshwater(cannot tolerate salinity) and brackish water, found both in the estuarine areas of the sea and in the lower reaches of rivers. The latter species are close to the species, feeding in brackish-water deltas, bays and estuaries, and spawning in rivers and floodplain lakes.

Truly freshwater fish are fish that live and reproduce only in fresh water (minnow).

A number of species that usually live in sea or fresh water can easily move to “atypical” water in new conditions. Thus, some gobies and pipefish have spread along the rivers and reservoirs of our southern rivers.

A separate group is formed migratory fish, spending most of their lives in the sea (feeding and maturing, i.e. growing in the sea), and on spawning coming into rivers or, conversely, i.e. making spawning migrations from rivers to seas.

These fish include many commercially valuable sturgeon and salmon fish. Some species of fish (salmon) return to the bodies of water where they were born (this phenomenon is called homing - home instinct). These abilities of salmon are actively used when introducing eggs into rivers that are new to these fish. The mechanisms that allow migratory fish to accurately find their home river or lake are unknown.

There are species that live most of their lives in rivers and go to the sea to spawn (i.e. vice versa). Among our fauna, such journeys are made by the river eel, which lives and matures in rivers and lakes, and goes into the Atlantic Ocean to procreate.

In migratory fish, when moving from one environment to another, it is noticeable metabolism changes(most often when the reproductive products mature, they stop feeding) and appearance(body shape, coloring, etc.). Often these changes are irreversible - many species after spawning die.

Pink salmon, or pink salmon (Oncorhynchus gorbuscha) in various life stages
(male and female during breeding season and oceanic phase)

The intermediate ecological group is formed by semi-anadromous fish- fish that breed in fresh water and go into the water to feed desalinated areas of the sea - the coastal zone of the seas, bays, estuaries.

Fish reproduction

Spawning - the most important stage in the life of fish.

Many fish don't care about eggs and sweep a huge number of eggs (for beluga up to several million) into the water, where their fertilization occurs. A huge number of eggs die, and from each female one, rarely two, survive. Here, the astronomical number of spawned eggs is responsible for the preservation of the species.

Some species of fish (gobies, sticklebacks) lay up to hundreds of eggs, but guard offspring, build peculiar nests, protect eggs and fry. There are even species, such as tilapia, that hatch eggs and larvae in the mouth. The number of eggs in these fish is small, but the survival rate is significantly higher, which ensures the preservation of the species.

Spawning site in most spawning fish it is characteristic of the species, and therefore there is their division into environmental groups according to the nature of spawning:

• pelagophiles spawn in the water column, most often on the current, where their development occurs (in suspension);
• lithophiles lay eggs on the ground;
• phytophiles - on aquatic vegetation.
• There are a few species that have found an extremely original substrate for their eggs: for example, bitterlings lay their eggs in the mantle cavity of bivalve mollusks.

Fish nutrition

Fish feeding patterns can vary greatly with age. Typically, juveniles are planktivores or benthophages, and with age they switch to predation. For example, fry