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 at 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 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 fish useful (necessary) 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. Oxygen concentration ranges within which embryo development is possible different types fish, vary significantly, with oxygen concentrations corresponding to the upper limits of these ranges far exceeding 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 in 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 great importance The question arises about the possibility of growing anadromous fish in brackish water from the very beginning of their development.

The influence of light. When carrying out incubation, it is necessary to take into account the fitness of embryos and prelarvae various types fish to light. 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. Exposure to direct sunlight inhibits the growth and development of sturgeon embryos and reduces the viability of prelarvae. This is due to the fact that sturgeon caviar naturally develops in muddy water and at considerable depth, that is, in low light. Therefore, when artificially reproducing 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 against Saprolegnia damage to eggs, they must be treated with a 0.5% formaldehyde solution for 30-60 seconds before loading them into incubation apparatus.

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, at early stages fragmentation of fertilized eggs, its embryogenesis, despite the increase in temperature, slows down, and with a greater increase, the death of 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 the hatching time.

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 is of paramount 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 farmed object or the mechanical use of 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 the 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.

Water as a living environment has a number of specific features, creating unique conditions of existence.

The life arena of fish is exceptionally large. With a common surface globe, equal to approximately 510 million square meters. km, about 361 million sq. km, i.e. 71% of the total area, is occupied by the surface of oceans and seas. In addition, about 2.5 million sq. km, or 0.5% of the globe's area, is occupied by inland water bodies. The vastness of the life arena is determined, in addition, by its large vertical extension. The maximum known depth of the ocean is approximately 11 thousand m. Oceans with a depth of more than 3 thousand m occupy approximately 51-58% of the total area of ​​​​sea waters. Further, it should be taken into account that fish live in areas located from the equator to the polar spaces; they are found in mountain reservoirs at an altitude of more than 6 thousand above sea level and in the oceans at a depth of more than 10 thousand m. All this creates a wide variety of living conditions. Let's look at some of the features of the aquatic habitat in relation to the fish that inhabit it.

The mobility of the aquatic environment is associated with constant currents in rivers and seas, local currents in small closed reservoirs, and vertical movements of water layers due to their different heating.

Water mobility largely determines the passive movements of fish. Thus, the larvae of Norwegian herring, which hatched off the coast of Western Scandinavia, are carried away by one of the branches of the Gulf Stream to the northeast and in 3 months travel along the coast for 1000 km.

The fry of many salmonids hatch in the heads of tributaries large rivers, and they spend most of their lives in the seas. The transition from rivers to seas is also accomplished largely passively; they are carried into the seas by river currents.

Finally, the mobility of water determines the passive movements of food objects - plankton, which in turn affects the movement of fish.

Temperature fluctuations in the aquatic environment are much smaller than in the air-terrestrial environment. In the overwhelming majority of cases, the upper temperature limit at which fish are found lies below +30, +40° C. It is especially characteristic lower limit water temperature, which even in highly salty parts of the oceans does not fall below -2° C. Consequently, the real temperature range of the fish habitat is only 35-45° C.

At the same time, it must be taken into account that these relatively limited temperature fluctuations are of great importance in the life of fish. The influence of temperature is carried out both by a direct effect on the fish’s body, and indirectly, through a change in the ability of water to dissolve gases.

As you know, fish belong to the so-called cold-blooded animals. Their body temperature does not remain more or less constant, like that of warm-blooded animals - it is directly dependent on temperature environment. This is due to the physiological characteristics of organisms, in particular to the nature of the heat generation process. In fish, this process is much slower. Thus, a carp weighing 105 g emits 42.5 kJ of heat per 1 kg of mass per day, and a starling weighing 74 g emits 1,125 kJ per 1 kg of mass per day. It is known that the temperature of the environment, and consequently the body temperature of fish, significantly influences such important biological phenomena as the maturation of reproductive products, the development of eggs, and nutrition. A decrease in water temperature causes a number of fish to hibernate. These are, for example, crucian carp, carp, sturgeon.

The indirect influence of water temperature can be clearly observed in the characteristics of gas exchange phenomena in fish. It is known that the ability of water to dissolve gases, and in particular oxygen, is inversely proportional to its temperature and salinity.

At the same time, fish's need for oxygen increases as water temperature rises. In connection with the above, the minimum oxygen concentration below which the fish dies also changes. For carp it will be equal to: at a temperature of 1°C - 0.8 mg/l, at a temperature of 30°C - 1.3 mg/l, and at 40°C - about 2.0 mg/l.

In conclusion, we point out that the oxygen requirement of different species of fish is not the same. On this basis, they can be divided into four groups: 1) requiring a lot of oxygen; normal conditions for them are 7-11 cm 3 of oxygen per liter: brown trout (Salmo trutta), minnow (Phoxinus phoxinus), loach (Nemachilus barbatulus); 2) requiring a lot of oxygen - 5-7 cm 3 per liter: grayling (Thymallus thymallus), chub (Leuciscus cephalus), gudgeon (Gobio gobio); 3) consuming a relatively small amount of oxygen - about 4 cm 3 per liter: roach (Rutilus rutilus), perch (Perea fluviatilis), ruff (Acerina cernua); 4) can withstand very low saturation of water with oxygen and live even at 1/2 cm 3 of oxygen per liter: carp, tench, crucian carp.

The formation of ice in water bodies is of great importance in the life of fish. The ice cover to a certain extent isolates the underlying layers of water from low temperatures air and thereby prevents the reservoir from freezing to the bottom. This makes it possible for the fish to spread into areas with very low winter temperatures. This is the positive value of ice cover.

Ice cover also plays a negative role in the life of fish. This is reflected in its darkening effect, which slows down or even almost completely stops the life processes of many aquatic organisms that are directly or indirectly of nutritional importance to fish. First of all, this concerns green algae and higher plants, which feed partly on the fish themselves and on those invertebrate animals that the fish eat.

Ice cover extremely sharply reduces the possibility of replenishing water with oxygen from the air. In many reservoirs in winter, as a result of putrefactive processes, the oxygen dissolved in the water is completely lost. A phenomenon known as the death of water bodies occurs. In our country, it is widespread and is observed in basins whose drainage area is largely associated with swamps (usually peat). Large death tolls were observed in the Ob basin. The swamp waters that feed the rivers here are rich in humic acids and ferrous compounds. These latter, when oxidized, remove oxygen dissolved in it from the water. It is impossible to replace it from the air due to the continuous cover of ice.

From the rivers of the vast territory of Western Siberia, fish begin to descend into the Ob in December and, following it down, reach the Ob Bay in March. In the spring, as the ice melts, the fish rises back (the so-called fish run). Deaths are also observed in the European part of Russia. They lead to death successful fight by constructing ice holes or by increasing the flow of a pond or lake. Pond farms with high technical equipment use compressors that pump water with oxygen. One of the fishing methods is based on the approach of fish to ice holes or to heated ditches specially constructed on the shores of the lake. It is curious that the settlement of beavers and muskrats on some reservoirs subject to death weakened this phenomenon, since gas exchange between reservoirs and the atmosphere is facilitated through the burrows, huts and other structures of these animals.

The sound conductivity of water is very high. This circumstance is widely used by fish, among which sound signaling is widely developed. It provides information both among individuals of one species and signals about the presence of individuals of other species. It is possible that the sounds made by fish have echolocation significance.

Ecological groups of fish

Sea fish

This is the largest group of species that spend their entire lives in salty sea water. They inhabit various horizons, and such groups should be distinguished on this basis.

1. Pelagic fish. They live in the water column, in which they move widely in search of food and places suitable for reproduction. The vast majority are active swimmers and have elongated, spindle-shaped bodies; such as, for example, sharks, sardines, mackerel. A few, such as the sunfish, move largely passively with water currents.

2. Littoral-bottom fish. They live in the bottom layers of water or at the bottom. Here they find food, spawn and escape persecution. Distributed at various depths, from shallow water (rays, some flounders, gobies) to significant depths (chimaeras).

The ability to swim is worse than that of the species of the previous group. Many have a variety of devices for passive protection in the form of thorns, thorns (some stingrays, gobies), and a thick outer shell (body).

3. Abyssal fish. A small group inhabiting deep-water (below 200 m) parts of the seas and oceans. The conditions of their existence are extremely peculiar and generally unfavorable. This is due to the absence of light at great depths, low temperatures (no higher than +4° C, more often about 0° C), enormous pressure, higher salinity of water, and the absence of plant organisms. Abyssal fish are partly devoid of eyes, while others, on the contrary, have huge telescopic eyes; some have luminous organs that facilitate the search for food. Due to the lack of plants, all abyssal fish are carnivorous; they are either predators or carrion eaters.

Freshwater fish

Freshwater fish live only in fresh water bodies, from which they do not even go to the salty pre-estuary areas of the seas. Depending on the type of reservoir, freshwater fish are divided into the following groups:

1. Fish of stagnant waters live in lakes and ponds (crucian carp, tench, some whitefish).

2. General freshwater fish inhabit standing and flowing waters (pike, perch).

3. Fish of flowing waters. As an example, we can point to trout and asp.

Migratory fish

Migratory fish depending on stage life cycle They live either in the seas or in rivers. Almost all migratory fish spend the period of growth and maturation of reproductive products in the sea, and go to rivers to spawn. These include many salmon (chum salmon, pink salmon, salmon), sturgeon (sturgeon, beluga), and some herrings. As an opposite example, we should point to river eels (European and American), which breed in the sea (Atlantic Ocean), and spend the period of preparation for spawning in rivers.

Fish of this group often make very long migrations of 1000 kilometers or more. So, chum salmon from the northern part Pacific Ocean enters the Amur, along which it rises (some shoals) above Khabarovsk. European eel from the Northern rivers Europe is coming to spawn in the Sargasso Sea, i.e., the western part of the Atlantic Ocean.

Semi-anadromous fish

Semi-anadromous fish live in pre-estuary desalinated parts of the seas, and for breeding, and in some cases for wintering, they enter rivers. However, unlike true migratory fish, they do not rise high in rivers. These are roach, bream, carp, and catfish. These fish can sometimes live and settle in fresh water bodies. The group of semi-anadromous fish is the least natural.

Body shape of some groups of fish

Due to the exceptional diversity of living conditions appearance fish is also extremely diverse. Most of the species inhabiting open spaces bodies of water, have a spindle-shaped body, often somewhat laterally compressed. These are good swimmers, since swimming speed in these conditions is necessary both for predatory fish when catching prey, and for peaceful fish forced to flee from numerous predators. Such are sharks, salmon, herring. Their main organ of forward movement is the caudal fin.

Among the fish that live in open parts of water bodies, the so-called planktonic fish are relatively few. They live in the water column, but often move passively along with currents. Externally, most of them are distinguished by a shortened but greatly expanded body, sometimes almost spherical in shape. The fins are very poorly developed. Examples include hedgehogfish (Diodon) and melanocetus (Melanocetus). The moon fish (Mola mola) has a very high body, laterally compressed. It does not have caudal or ventral fins. The pufferfish (Spheroides), after filling its intestines with air, becomes almost spherical and floats with the belly up in the current.

Bottom fish are much more numerous and diverse. Deep-sea species often have a drop-shaped shape, in which the fish has a large head and a body that gradually becomes thinner towards the tail. These are the longtail (Macrurus norvegicus) and the chimera (Chimaera monstrosa) from cartilaginous fish. Close in body shape to them are cod and eelpout, living in the bottom layers, sometimes at considerable depths. The second type of benthic deep-sea fish are stingrays, flattened in the dorsal-ventral direction, and flounders, flattened laterally. These are sedentary fish that also feed on slow-moving animals. Among the bottom fish there are species that have a serpentine body - eels, pipefish, and loaches. They live among thickets of aquatic vegetation, and their movement is similar to the movement of snakes. Finally, let us mention the peculiar bodies (Ostracion), the body of which is enclosed in a bony shell that protects the fish from the harmful effects of the surf.

Life cycle of fish, migration

Like all living beings, fish at different stages of their life path need various conditions environment. Thus, the conditions necessary for spawning differ from the conditions that ensure the best feeding of fish, unique conditions are needed for wintering, etc. All this leads to the fact that in search of conditions suitable for each given life function, fish make more or less significant movements. In species inhabiting small enclosed bodies of water (ponds, lakes) or rivers, movements are on an insignificant scale, although in this case they are still quite clearly expressed. In marine fish and especially in migratory fish, migrations are most developed.

The spawning migrations of migratory fish are the most complex and varied; they are associated with the transition from seas to rivers (more often) or, conversely, from rivers to seas (less often).

The transition for reproduction from seas to rivers (anadromous migrations) is characteristic of many salmon, sturgeon, some herring and carp. There are significantly fewer species that feed in rivers and go to the seas to spawn. Such movements are called catadromous migrations. They are characteristic of acne. Finally, and many purely sea ​​fish In connection with spawning, they make long movements, moving from the open sea to the shores or, conversely, from the coastal areas to the depths of the sea. These include sea herring, cod, haddock, etc.

The length of the spawning migration route varies greatly depending on the type of fish and the conditions of the water bodies they inhabit. Thus, species of semi-anadromous cyprinids in the northern part of the Caspian Sea rise up the rivers only a few tens of kilometers.

Many salmon make enormous migrations. For Far Eastern salmon - chum salmon - the migration route in some places reaches two thousand kilometers or more, and for sockeye salmon (Oncorhynchus nerka) - about 4 thousand km.

Salmon rises along the Pechora to its upper reaches. The European river eel, which breeds in the western part of the Atlantic Ocean, travels several thousand kilometers on its way to its spawning grounds.

The length of the migration route depends on how adapted the fish are to the conditions in which spawning can take place, and in this connection, on how far from the feeding areas the places suitable for spawning are located.

The timing of spawning migrations for fish generally cannot be specified as definitely as, for example, the timing of bird migrations to nesting grounds. This is due, firstly, to the fact that the timing of spawning in fish is very diverse. Secondly, there are many cases where fish approach spawning grounds almost six months before spawning. For example, White Sea salmon enters rivers at two times. In the fall, individuals with relatively underdeveloped reproductive products arrive. They overwinter in the river and breed the following year. Along with this, there is another biological race of White Sea salmon, which enters the rivers in the summer - the reproductive products of these individuals are well developed, and they spawn in the same year. Chum salmon also have two spawning runs. The “summer” chum salmon enters the Amur in June - July, the “autumn” chum salmon - in August - September. Unlike salmon, both biological races of chum salmon spawn in the year they enter the river. Vobla enters rivers to spawn in the spring; some whitefish, on the contrary, migrate to their breeding grounds only in the fall.

Here are generalized descriptions of the spawning migrations of some fish species.

Norwegian sea herring feed before breeding far to the north-west of Scandinavia, off the Faroe Islands, and even in the waters off Spitsbergen. At the end of winter, schools of herring begin to move towards the coast of Norway, which they reach in February-March. Spawning occurs in fiords near the shore in shallow places. Heavy caviar, swept by fish, settles in huge quantities to the bottom and sticks to algae and stones. The hatched larvae only partially remain in the fiords; a large mass of them is carried away by the North Cape Current (the northeastern branch of the Gulf Stream) along the coast of Scandinavia to the north. Larvae often begin such passive migration when they are still very young. early age when they retain a yolk sac. Three to four months before the end of July - beginning of August, they travel 1000 - 1200 km and reach the shores of Finnmarken.

Young herring make their way back actively, but much more slowly—over four to five years. They move south in stages every year, sometimes approaching the shores, sometimes moving out to the open sea. At four or five years of age, the herring becomes sexually mature, and by this time it reaches the spawning area - the place where it was born. This ends the first, “youthful” stage of her life - the period of a long journey to the north.

The second period, the period of maturity, is associated with annual migrations from feeding grounds to spawning grounds and back.

According to another hypothesis, migratory fish were originally marine fish and their entry into rivers was a secondary phenomenon associated with the strong desalination of the seas during the melting of glaciers, which in turn allowed the fish to more easily adapt to life in fresh water. One way or another, there is no doubt that migratory salmon change their habitats depending on the characteristics of their biological condition. Adult fish inhabit vast expanses of seas rich in food. Their young are hatched in cramped fresh water bodies (upper reaches of rivers), where it would be impossible for the entire mass of grown fish to exist due to the limited space itself and due to lack of food. However, conditions here are more favorable for hatching juveniles than in the sea. This is due to clean, oxygen-rich water, the possibility of burying eggs in the bottom soil and the possibility of their successful development in porous soil. All this is so conducive to the success of reproduction that the number of eggs ensuring the preservation of the species reaches, for example, only 1100-1800 eggs in pink salmon.

Feeding migrations on one scale or another are characteristic of almost all fish. Naturally, in small enclosed reservoirs, the movements of fish in search of food are very limited in nature and outwardly differ sharply from the long and massive wanderings observed in marine or migratory fish.

The nature of food migrations in a general sense is quite understandable, given that during the spawning period fish choose very specific environmental conditions, which, as a rule, are not of great value in terms of food. Let us remember, for example, that salmon and sturgeon spawn in rivers with their food capabilities being very limited for the huge masses of visiting fish. This circumstance alone should cause the fish to move after spawning. In addition, most fish stop feeding during reproduction, and therefore, after spawning, the need for food increases sharply. In turn, this forces the fish to look for areas with particularly favorable feeding opportunities, which enhances their movements. There are many examples of feeding migrations among various biological groups of fish.

European salmon - salmon, unlike its Pacific relative - chum salmon, does not die completely after spawning, and the movements of spawned fish down the river should be considered as feeding migrations. But even after the fish go to sea, they carry out mass regular migrations in search of places especially rich in food.

Thus, the Caspian stellate sturgeon, emerging from the Kura after spawning, crosses the Caspian Sea and feeds mainly off the eastern coast of the Caspian Sea. Young chum salmon, which migrate down the Amur next spring (after spawning), go to the shores of the Japanese Islands to fatten.

Not only anadromous fish, but also marine fish show examples of clearly defined feeding migrations. Norwegian herring, which spawn in the shallows off the southwestern coast of Scandinavia, do not remain in place after spawning, but move en masse to the north and northwest, to the Faroe Islands and even into the Greenland Sea. Here, on the border between the warm waters of the Gulf Stream and the cold waters of the Arctic basin, particularly rich plankton develops, on which emaciated fish feed. It is curious that simultaneously with the migration of herring to the north, the herring shark (Lanina cornubica) also migrates in the same direction.

Atlantic cod migrate widely in search of food. One of its main spawning sites is the shallows (banks) off the Lofoten Islands. After reproduction, cod becomes extremely voracious, and in search of food, large schools of it head partly along the coast of Scandinavia to the northeast and further east through the Barents Sea to the island of Kolguev and Novaya Zemlya, partly to the north, to Bear Island and further to Spitsbergen. This migration is of particular interest to us, since cod fishing in the Murmansk region and in the Kaninsko-Kolguevsky shallow waters is largely based on the catch of migrating and feeding schools. When migrating, cod adheres to the warm currents of the North Cape Current, through which, according to the latest data, it penetrates through the Kara Gate and Yugorsky Shar even into the Kara Sea. Largest quantity cod in the Barents Sea accumulates in August, but already in September its reverse movement begins, and by the end of November large cod that came from the coast of Norway disappears from our waters. By this time, the water temperature drops sharply and becomes unfavorable both for the fish themselves and for the animals that serve them as food. The cod, having fed and accumulated fat in the liver, begins to move back to the southwest, guided by the water temperature, which serves as a good reference point - an irritant during migrations.

The length of the one-way path taken by cod during the described migrations is 1-2 thousand km. Fish move at a speed of 4-11 nautical miles per day.

Along with horizontal migrations, there are known cases of vertical movements of marine fish in search of food. Mackerel rises to the surface layers of water when the richest development of plankton is observed here. When plankton sinks into deeper layers, mackerel also sinks there.

Wintering migrations. When water temperatures drop in winter, many species of fish become inactive or even fall into a state of torpor. In this case, they usually do not remain in feeding areas, but gather in limited spaces where the conditions of the topography, bottom, soil and temperature are favorable for wintering. Thus, carp, bream, pike perch migrate to the lower reaches of the Volga, Ural, Kura and others big rivers, where, accumulating in huge quantities, they lie in pits. The wintering of sturgeons in pits on the Ural River has long been known. In summer, our Pacific flounder are distributed throughout the Peter the Great Bay, where they do not form large aggregations. In autumn, as the water temperature drops, these fish move away from the shores into the depths and gather in a few places.
The physical reason that causes a kind of hibernation in fish is a decrease in water temperature. In a state of hibernation, fish lie motionless on the bottom, often in recesses of the bottom - pits, where they often accumulate in huge numbers. In many species, the surface of the body at this time is covered with a thick layer of mucus, which to a certain extent insulates the fish from negative action low temperatures. The metabolism of fish overwintering in this way is extremely reduced. Some fish, such as crucian carp, spend the winter burying themselves in mud. There are cases when they freeze into silt and successfully overwinter if the “juices” of their body are not frozen. Experiments have shown that ice can surround the entire body of a fish, but the internal “juices” remain unfrozen and have a temperature of up to -0.2, -0.3 ° C.

Wintering migrations do not always end with fish falling into a state of torpor. Thus, the Azov anchovy, after finishing its feeding period, leaves the Sea of ​​Azov for the Black Sea for the winter. This is apparently due to the unfavorable temperature and oxygen conditions that arise in the Sea of ​​Azov in winter due to the appearance of ice cover and the strong cooling of the water of this shallow reservoir.

A number of the above examples show that the life cycle of fish consists of a number of successively replacing each other stages: maturation, reproduction, feeding, wintering. During each stage of the life cycle, fish need different specific environmental conditions, which they find in different, often far apart places in the reservoir, and sometimes in different reservoirs. The degree of development of migration varies among different fish species. The greatest development of migration occurs in migratory fish and fish living in the open seas. This is understandable, since the diversity of habitat conditions in this case is very large and in the process of evolution, fish could have developed an important biological adaptation - significantly changing habitats depending on the stage of the biological cycle. Naturally, in fish inhabiting small and especially closed water bodies, migrations are less developed, which also corresponds to a lesser variety of conditions in such water bodies.

The nature of the life cycle of fish is different in other ways.

Some fish, and most of them, spawn annually (or at certain intervals), repeating the same movements. Others, during their life cycle, go through the stage of maturation of reproductive products only once, undertake spawning migration once, and reproduce only once in their lives. These are some types of salmon (chum salmon, pink salmon), river eels.

Nutrition

The nature of food in fish is extremely diverse. Fish feed on almost all living creatures that live in water: from the smallest planktonic plant and animal organisms to large vertebrates. At the same time, relatively few species feed only on plant foods, while the majority eat animal organisms or mixed animal-plant foods. The division of fish into predatory and peaceful is largely arbitrary, since the nature of food varies significantly depending on the conditions of the reservoir, time of year and age of the fish.

Particularly specialized herbivorous species are the planktonic common carp (Hyspophthalmichthys) and the higher vegetation eaters grass carp (Ctenopharyngodon).

Of the fish in our fauna, the predominantly plant species are the following: rudd (Scardinius), marinka (Schizothorax) and khramulya (Varicorhinus). Most fish feed on a mixed diet. However, at a young age, all fish go through the stage of peaceful feeding on plankton and only subsequently switch to their characteristic food (benthos, nekton, plankton). Among predators, the transition to the fish table occurs at different ages. Thus, pike begins to swallow fish larvae, reaching a body length of only 25-33 mm, pike perch - 33-35 mm; perch switches to fish food relatively late, with a body length of 50-150 mm, while invertebrates still constitute the main food of perch during the first 2-3 years of its life.

Due to the nature of nutrition, the structure of the oral apparatus in fish is significantly different. In predatory species, the mouth is armed with sharp, curved back teeth, which sit on the jaws (and in fish with a bony skeleton, often also on the palatine bones and on the vomer). Stingrays and chimeras, which feed on bottom invertebrates dressed in shells or shells, have teeth in the form of wide flat plates. In fish that chew corals, the teeth look like incisors and often grow together into one whole, forming a sharp cutting beak. These are the teeth of fused jaws (Plectognathi).

In addition to real jaw teeth, some fish also develop so-called pharyngeal teeth, which sit on the inner edges of the gill arches. In cyprinid fish, they are located on the lower part of the posterior modified gill arch and are called lower pharyngeal teeth. These teeth grind food against the horny callous area located on the underside of the skull, the so-called millstone. Wrasses (Labridae) have upper and lower pharyngeal teeth located opposite each other; in this case there is no millstone. In the presence of pharyngeal teeth, the real jaw teeth are either absent altogether or are poorly developed and only help in grasping and holding food.

Adaptation to the type of food is visible not only in the structure of the teeth, but also in the structure of the entire oral apparatus. There are several types of oral apparatus, the most important of which are the following:

1. The prehensile mouth is wide, with sharp teeth on the jaw bones, and often on the vomer and palatine bones. In this case, the gill rakers are short and serve to protect the gill filaments, and not to strain food. Characteristic of predatory fish: pike, pike perch, catfish and many others.

2. The mouth of the plankton eater is of medium size, usually not retractable; teeth are small or missing. The gill rakers are long and act like a sieve. Characteristic of herring, whitefish, and some cyprinids.

3. The suction mouth looks like a more or less long tube, sometimes extending. Works like a suction pipette when feeding on bottom invertebrates or small planktonic organisms. This is the mouth of the bream, the pipefish. This type of mouthparts was particularly developed in African longsnouts (Mormyridae), which, in search of food, thrust their tube-shaped snout under stones or into mud.

4. The mouth of a benthic eater - stingrays, flounders, sturgeons - is located on the underside of the head, which is associated with the extraction of food from the bottom. In some cases, the mouth is armed with powerful millstone-shaped teeth that serve to crush shells and shells.

5. Mouth with striking or sword-shaped jaws or snout. In this case, the jaws (garfish - Belonidae) or snout (rays, sawfish - Pristis, sawfish - Pristiophorus) are highly elongated and serve to attack schools of fish, such as herring. There are other types of oral apparatus, a complete list of which does not need to be given here. Let us note in conclusion that even in systematically similar fish, one can easily see differences in the structure of the mouth associated with the nature of their feeding. An example is carp fish, which feed either on bottom, or planktonic, or animals that fall to the surface of the water.

The intestinal tract also varies significantly depending on the nature of the diet. Predatory fish, as a rule, have a short intestine and a well-developed stomach. In fish fed with mixed or plant foods, the intestines are much longer, and the stomach is poorly separated or completely absent. If in the first case the intestine is only slightly longer than the body, then in some herbivorous species, for example, in the Trans-Caspian khramuli (Varicorhinus), it is 7 times longer than the body, and in the tomb (Hypophthalmichthys), which feeds almost exclusively on phytoplankton, the intestinal tract is 13 times longer than the body. fish body length.

The methods of obtaining food are varied. Many predators directly pursue their prey, catching it in open water. These are sharks, asp, pike perch. There are predators that lie in wait for prey and grab it at short notice. If the throw is unsuccessful, they do not attempt to chase the prey over a long distance. This is how pike and catfish hunt, for example. It was already indicated above that sawfish and sawfish use their xiphoid organ when hunting. They crash into schools of fish at high speed and make several strong blows with their “sword”, with which they kill or stun the victim. The insectivorous spray fish (T.oxotes jaculator) has a special device through which it throws out a strong stream of water, knocking insects off coastal vegetation.

Many bottom-dwelling fish are adapted to digging up the soil and selecting food items from it. Carp is able to get food, penetrating into the soil to a depth of 15 cm, bream - only up to 5 cm, while perch practically does not take food found in the soil at all. The American polytooth (Polyodon) and the Central Asian shovelnose (Pseudoscaphirhynchus) successfully dig in the ground, using their rostrum for this (both fish are from the cartilaginous subclass).

An extremely unique adaptation for obtaining food from electric eel. This fish, before grabbing its prey, strikes it with an electric discharge, reaching 300 V in large individuals. The eel can produce discharges randomly and several times in a row.

The feeding intensity of fish varies throughout the year and throughout the life cycle. The vast majority of species stop feeding during the spawning period and lose a lot of weight. Thus, in Atlantic salmon, muscle mass decreases by more than 30%. In this regard, their need for food is extremely high. The post-spawning period is called the period of restorative nutrition, or “zhora”.

Reproduction

The vast majority of fish are dioecious. The exceptions are a few bony fish: sea bass (Serranus scriba), sea bream (Chrysophrys) and some others. As a rule, in the case of hermaphroditism, the gonads alternately function as testes and as ovaries, and self-fertilization is therefore impossible. Only in sea bass, different parts of the gonad simultaneously secrete eggs and sperm. Sometimes hermaphroditic individuals are found in cod, mackerel, and herring.

In some fish, parthenogenetic development is sometimes observed, which, however, does not lead to the formation of a normal larva. In salmon, unfertilized eggs laid in the nest do not die and develop in a unique way until the time when embryos hatch from the fertilized eggs. This is a very peculiar adaptation to the preservation of the clutch, since if its unfertilized eggs developed and died and decomposed, this would lead to the death of the entire nest (Nikolsky and Soin, 1954). In Baltic herring and Pacific herring, parthenogenetic development sometimes reaches the stage of a free-swimming larva. There are other examples of this kind. However, in no case does parthenogenetic development lead to the formation of viable individuals.

In fish, another type of deviation from normal reproduction is known, called gynogenesis. In this case, sperm penetrate into the egg, but fusion of the nuclei of the egg and sperm does not occur. In some species of fish, development proceeds normally, but only females are produced in the offspring. This happens with silver crucian carp. In East Asia, both females and males of this species are found, and reproduction occurs normally. In Central Asia, Western Siberia and Europe, males are extremely rare, and in some populations there are none at all. In such cases, insemination, leading to gynogenesis, is carried out by males of other fish species (N Kolsky, 1961).

Compared to other vertebrates, fish are characterized by enormous fecundity. It is enough to point out that most species lay hundreds of thousands of eggs a year, some, for example cod, up to 10 million, and the sunfish even hundreds of millions of eggs. In connection with the above, the size of the gonads in fish is generally relatively large, and by the time of reproduction, the gonads increase even more sharply. There are often cases when the mass of the gonads at this time is equal to 25 or even more percent of the total body mass. The enormous fertility of fish is understandable if we consider that the eggs in the vast majority of species are fertilized outside the mother's body, when the probability of fertilization is sharply reduced. In addition, sperm retain the ability to fertilize in water for a very short time: for a short time, although it varies depending on the conditions in which spawning occurs. Thus, in chum salmon and pink salmon, which spawn in fast currents, where contact of sperm with eggs can occur in a very short period of time, sperm retain their mobility for only 10-15 seconds. For Russian sturgeon and stellate sturgeon, spawning on a slower current, it is 230 - 290 seconds. In Volga herring, a minute after placing sperm in water, only 10% of sperm remained motile, and after 10 minutes only a few sperm moved. In species that spawn in relatively low-moving water, sperm remain motile longer. Thus, in oceanic herring, sperm retain the ability to fertilize for more than a day.

When the eggs enter the water, they produce a glassy shell, which soon prevents sperm from penetrating inside. All this reduces the likelihood of fertilization. Experimental calculations have shown that salmon Far East the percentage of fertilized eggs is 80%. In some fish this percentage is even lower.

In addition, eggs, as a rule, develop directly in the aquatic environment; they are not protected or guarded in any way. Because of this, the probability of death of developing fish eggs, larvae and fry is very high. For commercial fish of the Northern Caspian Sea, it has been established that of all larvae hatched from eggs, no more than 10% rolls into the sea in the form of fully formed fish, while the remaining 90% die (Nikolsky, 1944).

The percentage of fish that survive to maturity is very small. For example, for stellate sturgeon it is determined at 0.01%, for autumn chum salmon of the Amur - 0.13-0.58, for Atlantic salmon - 0.125, for bream - 0.006-0.022% (Chefras, 1956).

Thus, it is obvious that the enormous initial fecundity of fish serves as an important biological adaptation for the conservation of species. The validity of this position is also proven by the clear relationship between fertility and the conditions under which reproduction occurs.

Marine pelagic fish and fish with floating eggs (millions of eggs) are the most fertile. The probability of death of the latter is especially high, since it can easily be eaten by other fish, thrown ashore, etc. Fish that lay heavy eggs that settle to the bottom, which also usually stick to algae or stones, have less fertility. Many salmon lay their eggs in holes specially constructed by fish, and some then fill these holes with small pebbles. In these cases, therefore, there are the first signs of “care for offspring.” Accordingly, fertility also decreases. Thus, salmon lays from 6 to 20 thousand eggs, chum salmon - 2-5 thousand, and pink salmon - 1-2 thousand. Let us point out for comparison that stellate sturgeon lays up to 400 thousand eggs, sturgeon - 400-2500 thousand, beluga - 300-8000 thousand, pike perch - 300-900 thousand, carp 400-1500 thousand, cod - 2500-10 000 thousand.

The three-spined stickleback lays eggs in a special nest built from plants, and the male guards the eggs. The number of eggs in this fish is 20-100. Finally, most cartilaginous fish, which have internal insemination, a complex egg shell (which they strengthen on stones or algae), lay eggs in units or dozens.

In most fish, fertility increases with age and only decreases slightly in old age. It should be borne in mind that most of our commercial fish do not live to the age of senescence, since by this time they are already caught.
As has already been partially indicated, the vast majority of fish are characterized by external fertilization. The exceptions are almost all modern cartilaginous fish and some bony fish. In the former, the outermost internal rays of the ventral fins function as a copulatory organ, which they fold together during mating and introduce into the female’s cloaca. There are many species with internal fertilization among the order of toothed carps (Cyprinodontiformes). The copulatory organ in these fish is the modified rays of the anal fin. Internal fertilization is characteristic of sea bass (Sebastes marinus). However, it does not have copulatory organs.

Unlike most vertebrates, fish (if we talk about the superclass in general) do not have a specific breeding season. Based on spawning time, at least three groups of fish can be distinguished:

1. Spawning in spring and early summer- sturgeon, carp, catfish, herring, pike, perch, etc.

2. Spawning in autumn and winter - these include mainly fish of northern origin. Thus, Atlantic salmon begins to spawn here from the beginning of September; The spawning period extends depending on the age of the fish and the conditions of the reservoir until the end of November. River trout spawn in late autumn. Whitefish spawn in September - November. Of the marine fish, cod spawns in Finnish waters from December to June, and off the coast of Murmansk - from January to the end of June.

As mentioned above, migratory fish have biological races that differ in the time of entry into rivers for spawning. Such races occur, for example, in chum salmon and salmon.

3. Finally, there is a third group of fish that do not have a specific reproduction period. These include mainly tropical species, temperature conditions whose habitats do not change significantly throughout the year. These are, for example, species of the family Cichlidae.

Spawning sites are extremely varied. In the sea, fish lay eggs starting from the ebb and flow zone, for example lumpfish (Cyclopterus), silverside (Laurestes) and a number of others, and to depths of 500-1000 m, where eels, some flounders, etc. spawn.

Cod and sea herring spawn off the coast, in relatively shallow places (banks), but outside the ebb and flow zone. Spawning conditions in rivers are no less varied. Bream in the lower ilmens of the Volga lay eggs on aquatic plants. Asp, on the contrary, chooses places with a rocky bottom and fast currents. Perches spawn in backwaters overgrown with algae and attach their eggs to underwater vegetation. In very shallow places, entering small rivers and ditches, pike spawn.

The conditions in which eggs are found after fertilization are very diverse. Most fish species leave it to its own devices. Some place caviar in special structures and more or less long time she is protected. Finally, there are cases when fish carry fertilized eggs on their body or even inside their body.

Let us give examples of such “care for offspring.” Chum salmon spawning grounds are located in small tributaries of the Amur, in places with pebble soil and relatively calm currents, with a depth of 0.5-1.2 m; In this case, it is important to have underground springs that provide clean water. The female, accompanied by one or several males, having found a place suitable for laying eggs, lies down on the bottom and, convulsively bending, clears it of grass and silt, raising a cloud of turbidity. Next, the female digs a hole in the ground, which is also done by striking her tail and bending her entire body. After constructing the pit, the spawning process begins. The female, being in the hole, releases eggs, and the male, located next to her, releases milt. Several males usually stand near the pit, and fights often occur between them.

Eggs are deposited in the pit in nests, of which there are usually three. Each nest is filled with pebbles, and when the construction of the last nest is completed, the female places an oval-shaped mound (2-3 m long and 1.5 m wide) above the hole, which guards it for several days, preventing other females from digging a hole here for spawning. Following this, the female dies.

An even more complex nest is made by the three-spined stickleback. The male digs a hole at the bottom, lines it with scraps of algae, then arranges the side walls and roof, gluing together the plant remains with the adhesive secretion of the skin glands. When finished, the nest has the shape of a ball with two holes. Then the male drives the females into the nest one after another and pours milk on each portion of eggs, after which he guards the nest from enemies for 10-15 days. In this case, the male is positioned relative to the nest in such a way that the movements of his pectoral fins excite the current of water passing over the eggs. This, apparently, ensures better aeration and, consequently, more successful development of eggs.

Further complications of the described phenomenon of “caring for offspring” can be seen in fish that carry fertilized eggs on their bodies.

In the female aspredo catfish (Aspredo laevis), the skin on the belly noticeably thickens and softens during the spawning period. After laying the eggs and fertilizing them by the male, the female presses the eggs into the skin of the belly with the weight of her body. Now the skin has the appearance of small honeycombs, in the cells of which eggs sit. The latter are connected to the mother's body by developing stalks equipped with blood vessels.

Male pipefish (Syngnathus acus) and seahorse (Hippocampus) have leathery folds on the underside of their bodies, forming a kind of egg sac into which females lay eggs. In the pipefish, the folds only bend over the belly and cover the caviar. In the seahorse, the adaptation to gestation is even more developed. The edges of the egg sac grow tightly together, and on the inner surface of the resulting chamber a dense network of blood vessels develops, through which, apparently, the gas exchange of the embryos occurs.

There are species that hatch eggs in their mouths. This happens with the American sea catfish (Galeichthys fells), in which the male carries up to 50 eggs in the mouth. At this time he apparently does not feed. In other species (for example, the genus Tilapia), the female carries the eggs in her mouth. Sometimes there are more than 100 eggs in the mouth, which are set in motion by the female, which is apparently associated with providing better aeration. The incubation period (judging by observations in the aquarium) lasts 10-15 days. At this time, females hardly feed. It is curious that even after hatching, the fry continue to hide in their mother’s mouth for some time when there is danger.

Let us mention the very peculiar reproduction of bitterling (Rhodeus sericeus) from the carp family, widespread in Russia. During the spawning period, the female develops a long ovipositor, with which she lays eggs in the mantle cavity of mollusks (Unio or Anodonta). Here the eggs are fertilized by sperm, sucked by the mollusks with a stream of water through a siphon. (The male secretes milk while near the clam.) The embryos develop in the gills of the clam and emerge into the water, reaching a length of about 10 mm.

The last degree of complexity of the reproduction process in fish is expressed in viviparity. The eggs fertilized in the oviducts, and sometimes even in the ovarian sac, do not enter the external environment, but develop in the mother’s reproductive tract. Typically, development is carried out due to the yolk of the egg, and only in the final stages the embryo is nourished by the secretion of a special nutrient fluid by the walls of the oviduct, which is received by the embryo through the mouth or through the squirter. Thus, the described phenomenon is more correctly designated as ovoviviparity. However, some sharks (Charcharius Mustelus) develop a kind of yolk placenta. It occurs by establishing a close connection between the blood-rich outgrowths of the yolk bladder and the same formations of the walls of the uterus. Metabolism in the developing embryo occurs through this system.

Ovoviviparity is most characteristic of cartilaginous fish, in which it is observed even more often than egg laying. On the contrary, among bony fish this phenomenon is observed very rarely. Examples include Baikal golomyankas (Comephoridae), blennies (Blenniidae), groupers (Serranidae) and especially toothed carp (Cyprinodontidae). All ovoviviparous fish have low fertility. Most give birth to a few cubs, less often dozens. Exceptions are very rare. For example, the blenny gives birth to up to 300 young, and the Norwegian blenny (Blenniidae) even up to 1000.

We have cited a number of cases when fertilized eggs are not left to the mercy of fate and fish show, in one form or another, care for them and the developing young. Such care is characteristic of a tiny minority of species. The main, most characteristic type of fish reproduction is one in which the eggs are fertilized outside the mother’s body and subsequently the parents leave them to their fate. This is precisely what explains the enormous fertility of fish, which ensures the preservation of species even in the event of a very large death of eggs and juveniles, which is inevitable under the specified conditions.

Height and age

The lifespan of fish varies greatly. There are species that live for little more than a year: some gobies (Gobiidae) and lantern anchovies (Scopelidae). On the other hand, the beluga lives to be 100 years or more. However, due to intensive fishing, the real life expectancy is measured in a few tens of years. Some flounders live 50-60 years. In all these cases, what is meant is the maximum potential life expectancy. Under conditions of regular fishing, the actual life expectancy is much less.

Unlike most vertebrates, as a rule, fish growth does not stop upon reaching sexual maturity, but continues throughout most of its life, until old age. Along with the above, fish are characterized by a clearly defined seasonal periodicity of growth. In summer, especially during the feeding period, they grow much faster than in the lean season. winter period. This uneven growth affects the structure of a number of bones and scales. Periods of slow growth are imprinted on the skeleton in
in the form of narrow stripes or rings consisting of small cells. When viewed in incident light, they appear light; in transmitted light, on the contrary, they appear dark. During periods of increased growth, wide rings or layers are deposited, which appear light in transmitted light. The combination of two rings - a narrow winter one and a wide summer one - represents the annual mark. Counting these marks allows you to determine the age of the fish.

Age is determined by scales and some parts of the skeleton.

Thus, by scales one can determine the number of years lived in salmon, herring, carp, and cod. The scales are washed in a weak solution of ammonia and viewed between two slides under a microscope and a magnifying glass. In perch, burbot and some other fish, age is determined by flat bones, for example, by the operculum and cleithrum. In flounder and cod fish, otoliths are used for this purpose, which are first degreased and sometimes polished.

The age of sturgeon, catfish and some sharks is determined by examining the cross section of the fin ray: in sharks - gypsy, in sturgeon - pectoral.

Determining the age of fish is of great theoretical and practical importance. In a rationally managed fishery, analysis of the age composition of the catch serves as the most important criterion for establishing overfishing or underfishing. Increased body density younger ages and a decrease in older ones indicates fishing pressure and the threat of overfishing. On the contrary, a large percentage of older fish indicates incomplete use of fish stocks. “So, for example, if in the catch of roach (Rutilus rutilus caspius) a large number of seven- and eight-year-old individuals will indicate, as a rule, undercatch (roach usually becomes sexually mature upon reaching the age of three), then the presence of individuals in the catch of sturgeon (Acipenser gtildenstadti) mainly at the age of 7-8 years will indicate a catastrophic situation in the fishery (sturgeon becomes sexually mature no earlier than 8-10 years of age), since immature individuals predominate in the studied sturgeon catch” (Nikolsky, 1944). In addition, by comparing the age and size of fish, important conclusions can be made about their growth rates, which are often related to the food supply of reservoirs.

CHAPTER I
STRUCTURE AND SOME PHYSIOLOGICAL FEATURES OF FISH

EXCRETORY SYSTEM AND OSMOREGULATION

Unlike higher vertebrates, which have a compact pelvic kidney (metanephros), fish have a more primitive trunk kidney (mesonephros), and their embryos have a pronephros. In some species (goby, silverside, eelpout, mullet), the preference in one form or another performs an excretory function in adult individuals; in most adult fish, the mesonephros becomes a functioning kidney.

The kidneys are paired, dark red formations extended along the body cavity, tightly adjacent to the spine, above the swim bladder (Fig. 22). The kidney is divided into an anterior section (head kidney), middle and posterior.

Arterial blood enters the kidneys through the renal arteries, venous blood through the portal veins of the kidneys.

Rice. 22. Trout kidney (according to Stroganov, 1962):
1 - superior vena cava, 2 - efferent renal veins, 3 - ureter, 4 - bladder

The morphophysiological element of the kidney is the convoluted renal urinary tubule, one end of which expands into the Malpighian corpuscle, and the other extends to the ureter. The glandular cells of the walls secrete nitrogenous breakdown products (urea), which enter the lumen of the tubules. Here, in the walls of the tubules, reabsorption of water, sugars, and vitamins from the filtrate of Malpighian bodies occurs.

The Malpighian corpuscle, a glomerulus of arterial capillaries, enclosed by the dilated walls of the tubule, forms Bowman's capsule. In primitive forms (sharks, rays, sturgeons), a ciliated funnel extends from the tubule in front of the capsule. The Malpighian glomerulus serves as a filtering apparatus for liquid metabolic products. The filtrate contains both metabolic products and substances important for the body. The walls of the renal tubules are penetrated by capillaries of the portal veins and vessels from Bowman's capsules.

Purified blood is returned to vascular system kidneys (renal vein), and metabolic products and urea filtered from the blood are excreted through the tubule into the ureter. The ureters drain into the bladder (urinary sinus), and then urine is excreted 91; in males of most bony fishes through the urogenital opening behind the anus, and in female bony fishes and males of salmon, herring, pike and some others - through the anus. In sharks and rays, the ureter opens into the cloaca.

In addition to the kidneys, the skin, gill epithelium, and digestive system take part in the processes of excretion and water-salt metabolism (see below).

The living environment of fish - sea and fresh water - always has more or less salts, so osmoregulation is the most important condition vital activity of fish.

The osmotic pressure of aquatic animals is created by the pressure of their cavity fluids, the pressure of blood and body juices. The decisive role in this process belongs to water-salt metabolism.

Each cell of the body has a membrane: it is semi-permeable, that is, it is differently permeable to water and salts (it allows water to pass through and is salt-selective). Water-salt metabolism of cells is determined primarily by the osmotic pressure of blood and cells.

According to the level of osmotic pressure of the internal environment in relation to the surrounding water, fish form several groups: in hagfish, the cavity fluids are isotonic to the environment; in sharks and rays, the concentration of salts in body fluids and osmotic pressure are slightly higher than in sea water, or almost equal to it (achieved due to the difference in the salt composition of blood and sea water and due to urea); in bony fish - both marine and freshwater (as well as in more highly organized vertebrates) - the osmotic pressure inside the body is not equal to the osmotic pressure surrounding water. In freshwater fish it is higher, in marine fish (as well as in other vertebrates) it is lower than in the environment (Table 2).

table 2
The magnitude of blood depression for large groups of fish (according to Stroganov, 1962)

Group of fish. Depression D°Blood. Depression D° External environment. Average osmotic pressure, Pa. Blood Average osmotic pressure, Pa
External environment.
Teleosts: marine. 0.73. 1.90-2.30. 8.9 105. 25.1 105.
Teleosts: freshwater. 0.52. 0.02-0.03. 6.4 105. 0.3 105.

If the body maintains a certain level of osmotic pressure of body fluids, then the living conditions of cells become more stable and the body is less dependent on fluctuations in the external environment.

Real fish have this property - to maintain relative constancy of the osmotic pressure of blood and lymph, i.e., the internal environment; therefore, they belong to homoiosmotic organisms (from the Greek “homoios” - homogeneous).

But in different groups of fish this independence of osmotic pressure is expressed and achieved in different ways,

In marine bony fishes, the total amount of salts in the blood is significantly lower than in sea water, the pressure of the internal environment is less than the pressure of the external environment, i.e. their blood is hypotonic in relation to sea water. Below are the values ​​of fish blood depression (according to Stroganov, 1962):

Type of fish. Environmental depression D°.
Marine:
Baltic cod - 0,77
sea ​​flounder - 0,70
mackerel - 0,73
rainbow trout - 0,52
burbot - 0,48

Freshwater:
carp - 0,42
tench - 0,49
pike - 0,52

Passing:
eel in the sea - 0,82
in a river - 0,63
sturgeon in the sea - 0,64
in a river - 0,44

In freshwater fish, the amount of salts in the blood is higher than in fresh water. The pressure of the internal environment is greater than the pressure of the external environment, their blood is hypertonic.

Maintaining the salt composition of the blood and its pressure at the required level is determined by the activity of the kidneys, special cells of the walls of the renal tubules (urea secretion), gill filaments (ammonia diffusion, chloride secretion), skin, intestines, and liver.

In marine and freshwater fish, osmoregulation occurs different ways(specific activity of the kidneys, different permeability of the integument for urea, salts and water, different activity of the gills in sea and fresh water).

In freshwater fish (with hypertonic blood) located in a hypotonic environment, the difference in osmotic pressure inside and outside the body leads to the fact that water from the outside continuously enters the body - through the gills, skin and oral cavity (Fig. 23).

Rice. 23. Mechanisms of osmoregulation in bony fishes
A – freshwater; B – marine (according to Stroganov, 1962)

In order to avoid excessive watering, to maintain the water-salt composition and the level of osmotic pressure, it becomes necessary to remove excess water from the body and simultaneously retain salts. In this regard, the kidneys develop powerfully in freshwater fish. The number of Malpighian glomeruli and renal tubules is large; they excrete much more urine than their relatives marine species. Data on the amount of urine excreted by fish per day are presented below (according to Stroganov, 1962):

Type of fish. Amount of urine, ml/kg body weight
Freshwater:
carp - 50–120
trout - 60– 106
dwarf catfish - 154 – 326

Marine:
goby - 3–23
angler - 18

Passing:
eel in fresh water - 60–150
at sea - 2–4

The loss of salts in urine, excrement and through the skin is replenished in freshwater fish by receiving them from food due to the specialized activity of the gills (the gills absorb Na and Cl ions from fresh water) and the absorption of salts in the renal tubules.

Marine bony fish (with hypotonic blood), located in a hypertonic environment, constantly lose water - through the skin, gills, with urine, and excrement. Preventing dehydration of the body and maintaining osmotic pressure at the desired level (i.e., lower than in sea water) is achieved by drinking sea water, which is absorbed through the walls of the stomach and intestines, and excess salts are released by the intestines and gills.

Eel and sculpin goby in sea water drink 50–200 cm3 of water per 1 kg of body weight every day. Under experimental conditions, when the water supply through the mouth (closed with a stopper) was stopped, the fish lost 12%–14% of their weight and died on the 3rd–4th day.

Marine fish secrete very little urine: they have few Malpighian glomeruli in their kidneys, some have none at all and only have renal tubules. Their skin permeability to salts is reduced, and their gills release Na and Cl ions. The glandular cells of the tubule walls increase the secretion of urea and other products of nitrogen metabolism.

Thus, in anadromous fish - only marine or only freshwater - there is one method of osmoregulation that is specific to them.

Euryhaline organisms (i.e., those that can withstand significant fluctuations in salinity), in particular migratory fish, spend part of their lives in the sea and part in fresh water. When moving from one environment to another, for example during spawning migrations, they endure large fluctuations in salinity.

This is possible due to the fact that migratory fish can switch from one method of osmoregulation to another. In sea water they have the same osmoregulation system as in marine fish, in fresh water - like in fresh water, so their blood in sea water is hypotonic, and in fresh water it is hypertonic.

Their kidneys, skin and gills can function in two ways: the kidneys have renal glomeruli with renal tubules, like in freshwater fish, and only renal tubules, like in marine fish. The gills are equipped with specialized cells (the so-called Case-Wilmer cells) capable of absorbing and releasing Cl and Na (whereas in marine or freshwater fish they act only in one direction). The number of such cells also changes. When moving from fresh water to sea, the number of cells that secrete chlorides increases in the gills of the Japanese eel. In the river lamprey, when rising from the sea to rivers, the amount of urine excreted during the day increases to 45% compared to body weight.

In some migratory fish, mucus secreted by the skin plays an important role in the regulation of osmotic pressure.

The anterior part of the kidney - the head kidney - performs not an excretory, but a hematopoietic function: the portal vein of the kidneys does not enter it, and in its constituent lymphoid tissue, red and white blood cells are formed and dead red blood cells are destroyed.

Like the spleen, the kidneys sensitively reflect the condition of the fish, decreasing in volume when there is a lack of oxygen in the water and increasing when metabolism slows down (in carp - during wintering, when the activity of the circulatory system is weakened), in case of acute diseases, etc.

The additional function of the kidneys in the stickleback, which builds a nest from pieces of plants for spawning: before spawning, the kidneys enlarge, a large amount of mucus is produced in the walls of the kidney tubules, which quickly hardens in water and holds the nest together.

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 differences in pressure, to different temperatures and minor changes in the salinity of water, but they do not have to find themselves in a completely new environment, which would require a complete restructuring of the entire physiological aspect 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 the blood and cavity fluid due to the extraction of salts from the body of the fish by the surrounding fresh water. 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 salt concentration during external environment and retain salts in your 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 .

Without knowledge of the anatomical features of fish, it is not possible to conduct a veterinary examination, since the diversity of habitats and lifestyles has led to the formation of different groups of specific adaptations in them, manifested both in the structure of the body and in the functions of individual organ systems.

Body Shape Most fish are streamlined, but can be spindle-shaped (herring, salmon), arrow-shaped (pike), serpentine (eel), flat (flounder), etc. There are fish of an indeterminate bizarre shape.

Fish body consists of a head, body, tail and fins. The head part is from the beginning of the snout to the end of the gill covers; body or carcass - from the end of the gill covers to the end of the anus; caudal part - from the anus to the end of the caudal fin (Fig. 1).

The head can be elongated, conically pointed or with a xiphoid snout, which is interconnected with the structure of the oral apparatus.

There are upper mouths (planktivores), final mouths (predators), lower mouths, as well as transitional forms (semi-upper, half-lower). On the sides of the head there are gill covers covering the gill cavity.

The body of the fish is covered with skin, on which most fish have scales- mechanical protection of fish. Some fish do not have scales (catfish). In sturgeons, the body is covered with bony plates (bugs). The skin of fish contains many cells that secrete mucus.

The coloring of fish is determined by the coloring substances of the pigment cells of the skin and often depends on the illumination of the reservoir, certain soil, habitat, etc. The following types of coloration are available: pelagic (herring, anchovy, bleak, etc.), thicket (perch, pike), bottom (minnow, grayling, etc.), schooling (some herring, etc.). The mating color appears during the breeding season.

Skeleton(head, spine, ribs, fins) of fish is bony (in most fish) and cartilaginous (in sturgeon). Around the skeleton there is muscle, fat and connective tissue.

Fins are organs of movement and are divided into paired (thoracic and abdominal) and unpaired (dorsal, anal and caudal). Salmon fish also have an adipose fin above the anal fin on their back. The number, shape and structure of fins is one of the most important features in determining the family of fish.

Muscular fish tissue consists of fibers covered with loose connective tissue on top. The peculiarities of the tissue structure (loose connective tissue and the absence of elastin) determine the good digestibility of fish meat.

Each type of fish has its own color of muscle tissue and depends on the pigment: pike has gray muscles, pike perch - white, trout - pink,

carp - most are colorless when raw and turn white after cooking. White muscles do not contain pigment and, compared to red ones, they contain less iron and more phosphorus and sulfur.

Internal organs consist of the digestive apparatus, circulatory (heart) and respiratory (gills), swim bladder and genital organs.

Respiratory The organ of the fish is the gills, located on both sides of the head and covered with gill covers. In living and dead fish, the gills, due to the filling of their capillaries with blood, are bright red.

Circulatory system closed. The blood is red, its amount is 1/63 of the mass of the fish. The most powerful blood vessels run along the spine, which easily burst after the death of the fish, and spilled blood causes redness of the meat and its subsequent spoilage (sunburn). The lymphatic system of fish is devoid of glands (nodes).

Digestive system consists of the mouth, pharynx, esophagus, stomach predatory fish), liver, intestines and anus.

Fish are dioecious animals. Genital organs in females there are ovaries (ovaries), and in males there are testes (milts). Eggs develop inside the ovule. The eggs of most fish are edible. The caviar of sturgeon and salmon fish is of the highest quality. Most fish spawn in April-June, salmon in the fall, and burbot in the winter.

swim bladder performs hydrostatic, and in some fish - respiratory and sound-producing functions, as well as the role of a resonator and converter of sound waves. Contains many defective proteins, it is used for technical purposes. It is located in the upper part of the abdominal cavity and consists of two, and in some cases, one sac.

Fish do not have thermoregulation mechanisms; their body temperature varies depending on the ambient temperature or only slightly differs from it. Thus, fish belong to poikilotherms (with variable body temperature) or, as they are unfortunately called, cold-blooded animals (P.V. Mikityuk et al., 1989).

1.2. Types of commercial fish

According to their lifestyle (aquatic habitat, characteristics of migration, spawning, etc.) all fish are divided into freshwater, semi-anadromous, anadromous and marine.

Freshwater fish live and spawn in fresh water bodies. These include those caught in rivers, lakes, ponds: tench, trout, sterlet, crucian carp, carp, etc.

Marine fish live and breed in the seas and oceans. These are herring, horse mackerel, mackerel, flounder, etc.

Migratory fish live in the seas and go to the upper reaches of rivers to spawn (sturgeon, salmon, etc.) or live in rivers and go to the sea to spawn (eel).

Semi-anadromous fish (bream, carp, etc.) live in river mouths and in desalinated areas of the sea, and breed in rivers.

More than 20 thousand fish are known, of which about 1,500 are commercial. Pisces having general signs Based on the shape of the body, the number and location of fins, skeleton, the presence of scales, etc., they are combined into families.

Herring family. This family is of great commercial importance. It is divided into 3 large groups: herring proper, sardines and small herrings.

Actually, herring fish are used mainly for salting and preparing preserves, canned food, cold smoking, and freezing. These include oceanic herring (Atlantic, Pacific, White Sea) and southern herring (blackback, Caspian, Azov-Black Sea).

Sardines combine fish of the genera: sardine proper, sardinella and sardicops. They have tight-fitting scales, a bluish-greenish back, and dark spots on the sides. They live in the oceans and are an excellent raw material for hot and cold smoking and canned food. Pacific sardines are called iwashi and are used to produce high-quality salted products. Sardines are an excellent raw material for hot and cold smoking.

Small herrings are herring, Baltic sprat (sprats), Caspian, North Sea, Black Sea, and also sprat. They are sold chilled, frozen, salted and smoked. Used for the production of canned food and preserves.

The sturgeon family. The body of the fish is spindle-shaped, without scales, and there are 5 rows of bony plates (clouds) on the skin. The head is covered with bony scutes, the snout is elongated, the lower mouth is in the form of a slit. The spine is cartilaginous, with a string (chord) running inside. Fatty meat is characterized by high taste qualities. Sturgeon caviar is especially valuable. Frozen sturgeon, hot and cold smoked, in the form of balyk and culinary products, and canned food go on sale.

Sturgeon include: beluga, kaluga, sturgeon, stellate sturgeon and sterlet. All sturgeons, except sterlet, are anadromous fish.

Salmon fish family. Fish of this family have silvery, tightly fitting scales, a clearly defined lateral line and an adipose fin located above the anus. The meat is tender, tasty, fatty, without small intermuscular bones. Most salmon are anadromous fish. This family is divided into 3 large groups.

1) European or gourmet salmon. These include: salmon, Baltic and Caspian salmon. They have tender, fatty meat that is light pink in color. Sold in salted form.

During the spawning period, salmon “put on” their nuptial plumage: the lower jaw lengthens, the color darkens, red and orange spots appear on the body, and the meat becomes thin. A sexually mature male salmon is called a sucker.

2) Far Eastern salmon live in the waters of the Pacific Ocean and go to spawn in the rivers of the Far East.

During spawning, their color changes, teeth grow, the meat becomes thin and flabby, the jaws bend, and pink salmon grow a hump. After spawning the fish dies. The nutritional value of fish during this period is greatly reduced.

Far Eastern salmon have delicate pink to red meat and valuable caviar (red). They go on sale salted, cold smoked, and in the form of canned food. Of commercial importance are chum salmon, pink salmon, chinook salmon, masu salmon, seal, and coho salmon.

3) Whitefish live mainly in the Northern Basin, rivers and lakes. They are small in size and have tender, tasty meat. white. These include: whitefish, muksun, omul, cheese (peled), vendace, whitefish. Sold in ice cream, salted, smoked, spicy salted and as canned food.

Cod family. Fish of this family have an elongated body, small scales, 3 dorsal and 2 anal fins. The meat is white, tasty, without small bones, but skinny and dry. They sell frozen and smoked fish, as well as in the form of canned food. Of commercial importance are: pollock, pollock, navaga, and silver hake. Cod also includes: freshwater and sea burbot, hake, cod, whiting and whiting, and haddock.

Fish of other families are of important commercial importance.

Flounder is caught in the Black Sea, Far Eastern and Northern basins. The body of the fish is flat, laterally compressed. Two eyes are located on one side. The meat is low-boned, of medium fatness. A representative of this family is the halibut, the meat of which contains a lot of fat (up to 19%), weighing 1-5 kg. Ice cream and cold smoked products are available for sale.

Mackerel and horse mackerel are valuable commercial fish up to 35 cm long, have an elongated body with a thin caudal peduncle. The meat is tender and fatty. They sell mackerel and Black Sea, Far Eastern and Atlantic mackerel, frozen, salted, hot and cold smoked. Also used for the production of canned food.

Horse mackerel, like mackerel, has the same catch regions, nutritional value and types of processing.

The following types of fish are also caught in the open seas and oceans: argentina, dentex, ocean crucian carp (from the spar family), grenadier (longtail), sabrefish, tuna, mackerel, mullet, saury, ice fish, notothenia, etc.

It should be borne in mind that many marine fish are not yet in great demand among the population. This is often explained by limited information about the merits of new fish and their taste differences from the usual ones.

Of the freshwater fish, the most widespread and numerous in the number of species is carp family . It includes: carp, bream, carp, silver carp, roach, ram, fisherman, tench, ide, crucian carp, saberfish, rudd, roach, carp, terech, etc. They have 1 dorsal fin, tight-fitting scales, a clearly defined lateral line , thickened back, terminal mouth. Their meat is white, tender, tasty, slightly sweet, of medium fat content, but it contains a lot of small bones. The fat content of fish of this family varies greatly depending on the species, age, size and place of catch. For example, the fat content of small young bream is no more than 4%, and large one - up to 8.7%. Carp are sold live, chilled and frozen, hot and cold smoked, canned and dried.

Other freshwater fish are also sold: perch and pike perch (perch family), pike (pike family), catfish (catfish family), etc.