Fish grow throughout their lives. However, this process is uneven. If young individuals grow quickly, then with age the relative increase in body weight decreases markedly. In summer, during the period of active feeding, intensive growth is observed, while in winter this process slows down, and in some species, for example, carp, it stops altogether due to the fact that at low temperatures it stops feeding.

The growth of fish is affected by the quality of water, as well as the availability of food. Growth also slows down after puberty, so young fish are of greatest interest for commercial cultivation. Typically, fish are grown in pond farms for 1-2 years. During this time, it reaches marketable weight (table).

Standard and maximum weight of fish grown in ponds by the end of the season, g

Carp	Regulatory	Maximum	Regulatory	Maximum
	25-30 g	500 g	350-500 g	1500 g

When choosing a growing object, you need to keep in mind that the growth rate of fish is far from the only indicator. It is also necessary to take into account the quality of water, food supply and the climatic zone in which the farm is located. In relation to the water temperature, all fish bred in fish farms are divided into heat-loving and cold-loving. The first group includes most cultivated fish. There are two known methods of growing fish in fish farming: extensive and intensive. With the extensive method, the fish are not fed. It grows only by eating natural food. This is essentially pasture-based fish farming. It allows you to obtain fish products at minimal cost. This direction is promising in the southern regions and in large reservoirs, where it is possible to effectively grow carp together with herbivorous fish. The intensive method of cultivation includes feeding the fish and creating a rich food supply through fertilization and reclamation of reservoirs. In modern fish farming, there are various technologies for intensive fish farming. Familiarization with them will allow you to choose the most appropriate one for your specific conditions.

The most widely used is traditional technology, which includes a two- or three-year fish farming cycle. According to this technology, carp and herbivorous fish are usually grown. In this case, ponds of various categories are used: spawning, fry, nursery, wintering, feeding. Each category of ponds is designed to perform a specific technological cycle. An option is possible in which there are no nursery ponds and planting material is purchased from another farm. Fish are grown at different levels of intensification. With a high level of intensification (multiple feeding, joint cultivation of several species of fish at high planting densities), it is possible to obtain fish products at a rate of 5-6 t/ha. The effectiveness of this method of cultivation requires compliance with a number of requirements: constant flow, technical aeration of water, regular liming of ponds.

In recent years, a simpler scheme for growing commercial fish has been proposed - according to the so-called continuous technology. It involves growing juvenile carp to a weight of 1-2 g and then raising them without transplants in one pond for two years. In this case, only two categories of ponds are required - fry and feeding ponds, where fish are raised and wintered.

One of the methods acceptable for owners of small ponds is the cultivation of commercial fingerlings. This technological scheme provides for early production of larvae, growing them in warm water to a weight of 1 g and their subsequent rearing in a pond with sparse planting. With a good food supply and a favorable hydrochemical regime, it is possible to obtain commercial fingerlings weighing 0.4-0.5 kg in one season.

High-intensity method of fish farming - growing fish in cages and pools. Cages are installed in cooling ponds of energy facilities or natural reservoirs (lakes, reservoirs). Growing fish in cages installed in cooling ponds is especially promising. In summer, heat-loving fish, such as carp, are grown in cages, and trout in winter. The use of this or that technology is also related to what types of fish you are going to grow.

Growing carp. The simplest and most affordable way to grow this fish is to stock the reservoir with yearlings in the spring and catch them in the fall. By this time, the carp reaches marketable weight. If it is not possible to purchase yearlings, then you can stock the reservoir with fry using the method of raising marketable fingerlings. If it is difficult to purchase planting material and you decide to breed carp yourself, you should keep in mind that this will require separate categories of ponds for breeding, growing and wintering fish. For those who want to specialize in the production of planting material, we provide basic information on the reproduction and rearing of juvenile carp. Timely stocking of the pond with your own planting material will allow you to avoid the costs of purchasing, transporting, and wintering. In this way, fish farming will be more manageable and therefore more efficient.

Female carp are very fertile, so you only need a few males and females. With natural spawning, the ratio of males to females is 2:1, with artificial insemination of eggs - 1:1. Manufacturers' shelf life is 5-7 years. Breeders should be kept freely: in a pond with an area of ​​100 m2 there should be no more than one nest (1 female and 2 males). Pre-spawning maintenance of spawners is important. In the spring, at a temperature of 8-10 °C, they need to be fed. Feed mixtures must contain at least 30 % feed of animal origin.

For breeding, it is necessary to use high-quality males and females, without injuries, with clearly defined sexual characteristics. It is difficult to determine the sex of carp, and impossible for immature individuals. Only with the onset of the spawning season can males be distinguished from females. In females, the genital opening is larger, somewhat swollen, reddish, the abdominal cavity is enlarged, soft to the touch. In males, the genital opening is a narrow, pale-colored slit; hard warts appear on the head and gill covers - a kind of mating plumage. When pressing on the abdomen, milk may be released.

Spawning results depend both on the quality of the spawners and on the preparation of the pond. Carp lay their eggs on a substrate, so there should be soft aquatic vegetation on the pond bed. If there is no vegetation, then for this purpose you can use turf, branches of coniferous trees, or prepare an artificial spawning ground (Fig. 35). Spawning takes place at a water temperature of 17-18 "C. The female lays eggs on vegetation or on an artificial spawning ground, and the males fertilize her. The duration of development of fertilized eggs, depending on the water temperature, is 3-5 days. The amount of heat required for the complete development of eggs is 60-80 degrees days.The most favorable temperature for embryonic development of carp is 18-26 °C.

Rice. 35. Artificial spawning ground

The hatched embryos are inactive for the first one or two days and live off the nutrients of the yolk sac, but then they begin to move and actively feed. They first consume rotifers, small forms of crustaceans and algae, then move on to larger crustaceans and chironomid larvae.

One of the main conditions for obtaining large mass and good fatness in the fall of the yearlings is to provide them with a sufficient amount of natural food. This is especially important in the first half of the growing season, when juveniles need food high in protein, vitamins and minerals.

From one nest of producers, 70-100 thousand larvae are obtained. The natural food resources of a small pond will clearly not be enough to adequately feed the larvae. Therefore, already on the 5-7th day the pond must be fished. During further cultivation of carp, the density of larvae should not exceed 10 specimens/m2.

If carp fry are taken from another body of water, then before putting the fish into your own pond, it is necessary to gradually equalize the temperature of the water in the container where the fish is located with the temperature of the water in the reservoir. Otherwise, the fish may die from temperature shock. To effectively develop the natural food supply, ponds are limed and fertilized. The dose of slaked lime added to the pond depends on the pH of the water (table).

Norms for adding slaked lime to a reservoir, kg/m2

pH		Soil bottom
Less than 4 4.0-4.5 4.51-5.0 5.01-5.5 5.51-6.0 6.01-6.5	clayey and loamy 0,42 0,32 0,27 0,17 0,12 0,07	sandy loam 0,22 0,17 0,15 0,12 0,07 0,05	sandy 0,18 0,15 0,12 0,07 0,05 0,02

The addition of lime has a preventive effect, preventing many fish diseases, and also helps to improve the hydrochemical regime of the reservoir. Lime neutralizes soil acidity, transforms accumulated organic matter into a harmless state, and helps enrich water with nutrients. Thus, lime has both a preventive, reclamation and, to a certain extent, fertilizing effect.

An increase in natural food reserves is facilitated by the addition of mineral and organic fertilizers to the pond. Organic fertilizers (manure) are applied in small doses at the water's edge. Adding a large amount of manure can cause a deterioration in the hydrochemical regime, so it is advisable to simultaneously add mineral fertilizers to the reservoir.

Mineral fertilizers (nitrogen and phosphorus), stimulating the development of phytoplankton, help increase the oxygen content in water. Ammonium nitrate and superphosphate are pre-dissolved in separate containers, after which they are added to water at the rate of 5 kg of each type of fertilizer per 1000 m 2. Fertilize once every 10 days. Frequency of application fertilizer is determined by the level of algae development in the pond. If algae develop intensively, fertilizers should not be applied. You can determine the need for fertilizer in a reservoir using a white disk, which determines the transparency of the water. The disc is lowered into the water to the depth to which it is visible. If the visibility line is at a depth of no more than 25-30 cm, then there is no need to apply fertilizer; if at a depth of 50 cm or more, then the pond should be fertilized.

Rice. 37. Feeder “Reflex”: 1 - feed container; 2 - rack; 3 - bridge; 4 - pendulum

In addition to natural food, juveniles need additional feeding. During the initial period of growing (in the first month), you need to feed the fish 1-2 times a day. As the water temperature rises, the number of feedings should be increased. For the convenience of distributing feed, you can use Reflex feeders (Fig. 37), which allow you to reduce its consumption.

During the entire growing period, it is necessary to monitor the growth of fish. To do this, control catches are done 1-2 times a month. At each control catch, the caught fish (15-25 specimens) are weighed and measured, and then released into the pond.

Juvenile growth chart carp

Control catch date	Number of days after hatching	Weight of fish, g
July 1
July 15	In order to leave the fish grown over the summer for the winter, it is necessary to carry out work to prepare the reservoir and the fish itself. Only those reservoirs that have deep places are suitable for wintering. For the central regions of the country, where the ice thickness reaches 80-100 cm, the depth of the pond should be at least 2 m. For the southern regions, where reservoirs do not freeze or freeze for a short period, the depth of the pond should be such that the non-freezing layer of water is at least 1m. Before wintering, it is advisable to pass the fish through salt baths. To do this, you need to prepare a saline solution at the rate of 1 kg of table salt per 20 liters of water. The fish should be caught from the pond and placed in a salt bath for 5 minutes, and then in a container with running water for 2-3 hours. The stocking density of carp fingerlings for wintering is 50-80 individuals/m2. For a successful wintering outcome for carp underyearlings, it is necessary to maintain a stable oxygen content in the water at the rate of 5-8 mg/l. If the amount of oxygen is 4 mg/l or less, then the water must be aerated, that is, enriched with oxygen. The simplest way is to create an ice hole. If it is possible to supply fresh water to the pond, you should do so. You can also use a compressor to supply air to the pond. In winter, carp underyearlings are not fed. They start feeding the fish in the spring at a water temperature of 8-10 °C. When starting the second year of growing carp, it is necessary to know the condition of the yearlings after wintering. If their weight is at least 25 g and their fatness is high, then wintering was successful and this is the key to successful cultivation of table fish. The density of planting yearlings of carp in a reservoir for growing commercial fish should be determined by the planned output of fish products per unit of pond area, as well as the natural food resources of the pond and the availability of compound feed. An example of calculating the density of carp yearlings, provided that the planned productivity of the pond is 1500 kg/ha, the area is 0.05 ha, the weight of two-year-olds by autumn is 0.5 kg, the average weight of spring yearlings is 0.03 kg, the fish yield of the planted amount is 90%: X= (1500 0.05 100) : (0.5 - 0.03)90 = 180 copies. In summer, the fish are fed twice a day. As a rule, in September, when the fish reaches marketable weight, they begin to fish the pond. Considering that fish grow unevenly, and also that individual individuals can reach marketable weight as early as July - August, it is advisable to catch them earlier. This extends the period of use of fresh fish for food. Thanks to the sparse planting, the fish remaining in the pond will be kept in better conditions and will reach marketable weight faster. Carp can be left for cultivation in the third year. In the third year, carp gives greater weight gain than in the second year of life. Typically the gain is about 1 kg. Three-year-old fish has more edible parts and its meat is richer in nutrients.

This is a very interesting question that worries many anglers. Although, on the other hand, this is not entirely important if there are no restrictions on fishing. Some of them determine the approximate age of the fish by size. But the size and weight of the fish may depend on a number of factors, including the availability of food in the reservoir. Therefore, this approach gives only approximate results, although quite satisfactory.

There is another way by which you can find out a more accurate age of a fish, just as you can calculate the age of a tree from a cut using its annual rings. You can find out about this by the scales, if you look at them carefully, by the bones and gills. Specialists involved in this field know almost everything about fish: what age they are, how intensively they grew, how many times they spawned, etc. In other words, fish scales are like a business card, or more precisely, like a passport.

If you look at the scales with a microscope, you can see peculiar rings on it, very similar to those observed on a cut of a tree. Each ring is a witness to another year lived. Based on the scales, it is possible to determine both the age of the fish and its length by which it has grown over the previous year.

Specimens up to 1 meter long have scales with a radius of up to 1 centimeter. The distance from the annual ring (initial) to the central part of the scale is about 6 mm. Using this information, it can be determined that the fish has grown by 60 cm over the year.

If you look at the scales under a microscope, you will notice another, but very important feature - the unevenness of the surface. On the scales you can see ridges and depressions, which are also called sclerites. Over the course of one year of life, 2 layers of sclerites appear - large and small. A large sclerite indicates a period of active growth of the fish, and a small one indicates that the fish has experienced the autumn-winter period.

If you accurately determine the number of double sclerites, you can simply determine the age of the fish. But, even in this case, you need to have certain skills.

But this is not a problem if the fish has large scales. At the same time, there are species of fish that have rather small scales and this method is not suitable, since it is not possible to calculate how long the fish lived. That is, it is possible to calculate it, but this will require special equipment. In this case, to calculate the age of the fish, the skeleton is taken as a basis. Based on this, we can conclude that it is not at all easy for an ordinary person to cope with this task, since the process requires special tools.

How do annual rings appear in fish?

To correctly and accurately determine the age of a fish, it is necessary to know the physiology of growth of annual rings.

If you look closely, you will notice that the rings are distributed in certain stages: after the wide and light rings there are narrow and dark rings. A wide ring indicates moments when the fish was actively growing and developing. As a rule, this is spring, summer and autumn. The dark ring forms when the fish is in cold water and with little to no food. Sometimes it is difficult to identify dark rings on fish, which indicates difficult wintering conditions.

Such rings are formed because the bones of the fish and its scales are endowed with such a feature as the appearance of layers, depending on living conditions. On the other hand, uniform development of scales or skeleton is only possible if the fish is in ideal conditions, which never happens.

Each year of a fish's life does not remain unmarked on the scales or fish bones. At first, the scale consists of a transparent plate. A year later, a second plate forms under it, which extends beyond the edge of the first. Then the third, then the fourth, etc. If the fish is about 5 years old, then its scales consist of 5 plates, one after the other. This arrangement is reminiscent of a layer cake, when the smallest but oldest plate is on top, and the largest but youngest plate is below.

How can you see the annual rings of fish?

It is very problematic to count or detect annual rings in fish, especially with the naked eye. Therefore, you need to have a magnifying glass or binoculars if everything happens on a pond. If you decide to deal with this problem at home, then it is better to arm yourself with a microscope. Before the process itself you need:

• Prepare the scales for inspection and, if necessary, wash them with alcohol.
• For inspection, it is better to take the largest scales, which are located on the sides.
• The scale should not have mechanical damage.

For more accurate calculations, it is necessary to take into account the absolute and relative size of sclerites. Under a microscope, annual rings, ridges and depressions will be visible. After several such approaches, it is possible to determine the age of the fish realistically and with great accuracy.

How is the age of a fish calculated?

Using scales and bones, you can determine with some accuracy the age of the fish or its growth a year earlier. To do this you will need a microscope and some tools. Based on the state of the scales, it is possible to determine what happened to the fish during spawning periods, for example. In some species of fish, when they go to spawn, their scales break off. Based on this factor, you can determine how many times the fish has already spawned in its life.

It is always easier to determine the age of a fish if it has thin but long scales. Thus, it is much easier to determine the age of pike, taimen, grayling, herring and many other species of fish.

It is much more difficult to determine the age of perch, burbot or eel. In this case, you will have to take flat bones as a sample. The age of sturgeon is determined by the large rays of the dorsal fins. To do this, take the largest beam and cut it at its widest point. Then the cut area is polished until transparent, after which the annual rings can be seen. After this, the age is calculated using the generally accepted method, which is applied to scales. This approach is used to determine the age of other fish species, such as catfish.

In addition to these methods, there is another method, which is based on the study of gills. Marks similar to those on the scales remain on the gill covers after each year. Scientists have determined that even fish that do not have a skeleton have their own annual rings. Such rings are formed on the thick rays of the pectoral fins.

To determine the abundance of a particular fish species, it is necessary to understand how dynamically a particular fish species develops. There are species that spawn quite late. If you take Amur salmon, they only begin to spawn at the age of 20. And so, if you go through individual species, you can understand that each species develops absolutely independently of one another and each species lives for a certain period of time. It is very important for science to know how long a particular species of fish can live in order to control the populations of certain species of fish. As for fishermen, for them the approximate age of the fish does not mean anything significant.

Fish reproduction.

Our freshwater fish reproduce almost exclusively by spawning - females spawn eggs, and males fertilize them with milk. Sexual maturity in most fish occurs in the third or fourth year of life, in smelt - in the first, in pike - in the second, in the eel - no earlier than the sixth, and sometimes in the twentieth, in beluga - in the twelfth-fifteenth.

The timing of puberty may vary depending on environmental conditions. For example, the Chud whitefish, acclimatized in Lake Sevan, reaches sexual maturity two years earlier than in its native lake. Carp in the central zone of the USSR becomes sexually mature in the fourth or fifth year of life, and in the Caucasus - in the second or third. In some cases, under unfavorable external environmental conditions, fish reproductive products do not mature and their degeneration and resorption occur.

Typically, fish spawn several times during their lives, while eels and Far Eastern salmon spawn once, after which they die. A significant percentage of mortality after spawning is observed in northern and Baltic salmon. Long-living fish (for example, pike and carp) lose their ability to reproduce in old age.

The process of spawning, called spawning, also occurs in fish under certain environmental conditions. Most fish spawn in the spring, salmon, whitefish and trout in the fall, and burbot in the winter. Spawning of each species of fish begins at a certain water temperature. For example, burbot spawns at a water temperature of about 0°, whitefish 1-3°, salmon 3-8°, perch 7-8°, roach about 10°, bream 12-14°, carp at a water temperature of about 151° and above .

The duration of spawning varies among different fish. Salmon, whitefish, roach, perch, and pike spawn eggs in a short time. In carp, crucian carp, tench, silver bream, and ruffe, eggs do not mature at the same time, and they throw them in parts. This “portioned” spawning helps preserve the species. For example, with a sharp cold snap and a rapid loss of water, not all eggs will die, but only part of it. In addition, with “portioned” spawning, the concentration of hatched larvae decreases and the growing fish receives more food.

Spawning sites are varied. More often, fish choose shallow, well-warmed areas of reservoirs. Pike and carp spawn on the fields; perch, bream, and roach spawn on coastal aquatic vegetation. Some fish spawn on fast, often pebble rifts (trout, grayling, chub, barbel), less often - in the water column(chekhon) or at great depths (eel).

The choice of one or another spawning site for various fish is not accidental. This is due to the properties of the eggs and the lifestyle of the hatching larvae and growing fry. For example, asp, chub, and podust, which spawn in fast currents, have sticky eggs, which protects them from being carried away by the current. Their larvae are afraid of light, hide under stones and other shelters, and this saves them from enemies. Fish have the same sticky eggs, laying them in quiet backwaters on aquatic vegetation. Here, eggs develop better in the water column, since, having fallen to the bottom, they find themselves in unfavorable oxygen conditions (oxygen in such places is spent on rotting plants). The larvae of these fish have glands on their heads that secrete a sticky substance that allows them to stick to aquatic plants and develop in the most favorable conditions.

Most fish spawn near their permanent habitats (pike, chub, barbel). Some make large spawning movements, or spawning migrations, in search of favorable conditions for the development of eggs and the subsequent life of the young. Eels travel the farthest - they spawn in the depths of the Atlantic Ocean. Migratory fish - salmon, nelma, sturgeon - rise into the rivers for hundreds and sometimes thousands of kilometers. Bream, pike perch, ide, and grayling often lead a semi-anadromous lifestyle, rising short distances into streams and rivers to spawn.

Spawning is usually massive; many females and males participate in it simultaneously. Mass spawning is observed in bream, ide, and perch. Some fish (for example, salmon and pike) are characterized by nesting reproduction, in which one female and several males spawn at the same time. Occasionally, a nest consists of only one female and one male, as in catfish or large carp.

In most cases, after spawning, fish immediately leave the spawning grounds and do not care about the further fate of the offspring. In this respect, salmon differ sharply in that before spawning they drive away all fish from the spawning area. Moreover, they lay their eggs in specially dug depressions in the pebble soil and cover them on top with pebbles and sand. Catfish also take care of the eggs, and the male even protects them until the fry hatch. Caring for the offspring of sticklebacks goes even further. The male stickleback builds a special nest from aquatic plants. The eggs are laid and fertilized in the nest, and the male, being at the entrance, guards the eggs and hatched fry.

Females of different fish lay unequal numbers of eggs. The largest numbers (sometimes over a million pieces) are thrown by carp, pike perch, and burbot; the smallest are salmon and whitefish. High fertility of fish is necessary for the preservation of the species, since during the development of eggs into adult fish, a very large percentage of eggs and fry die. The established percentage of commercial survival of bream ranges from 0.0006 to 0.014%, i.e., if we take the average fecundity of a female bream at the age of three equal to 100,000 eggs, then only two or three females survive to the first spawning.

The development of eggs in fish with spring spawning is short. The fry of carp hatch after 6-8 days, ide - after 8-12, pike - after 14-20 days. The development of eggs in fish with autumn or winter spawning lasts 5-6 months, since otherwise the larvae and growing juveniles would not find food for themselves.

The hatched larvae at first cannot obtain food and feed on substances contained in the yolk sac attached to their abdomen, but soon the yolk sac dissolves and the larva turns into a fry, which switches to independent active feeding.

Growth rates and sizes of fish.

The growth rates and sizes that fish reach are not the same in different reservoirs and depend mainly on the hydrobiological conditions of the environment, which, in turn, are associated with the physicochemical, climatic and soil characteristics of the reservoir. According to the hydrobiological regime, reservoirs are divided into three main types: low-feed, forage and non-feed.

Poorly fed reservoirs have clear, cold water with a small amount of nutrient salts. The water reaction is close to neutral, oxygen saturation is good, the bottom is rocky or sandy with poorly developed aquatic vegetation. This type includes mountain lakes and rivers, many of the lakes of the Karelian Autonomous Soviet Socialist Republic and the Karelian Isthmus.

In feeding ponds, the water is less transparent and contains a sufficient amount of nutrient salts. The water reaction and oxygen regime are different, the bottom is mostly silty-sandy, with well-developed vegetation. Most slow-flowing rivers and lowland lakes belong to this type.

Non-feeding ponds have dark brown water. The reaction is in most cases acidic, oxygen saturation is moderate, the bottom is most often peaty, and the vegetation is monotonous. This type of reservoir mainly includes small forest lakes in the northern part of the USSR.

Each type of fish chooses a certain type of reservoir in accordance with its characteristics. Trout and whitefish prefer the first type of lakes and it is in them that they reach their largest sizes. Bream, ide and pike perch grow best in feeding ponds.

In nature, there are many bodies of water that occupy an intermediate position between the described types, and often it is impossible to predict the growth rate and maximum size of the fish found in them. An angler who begins fishing in an unfamiliar body of water first of all wants to know what size fish he can count on. This does not require a detailed study of the reservoir. Growth rates can be determined by the age of the first fish caught in the reservoir.

For example, a perch at a normal growth rate should weigh 20 g at the age of two years, 50-60 g at the age of three, 90-100 g at four years, 150-200 g at the age of five, etc. If it turns out that the specimen under study is at the age of five years old weighs 50 g, which means the regime of the reservoir is not favorable for the life of perch and the largest specimen is unlikely to weigh more than 150-200 g. On the contrary, if at the age of five the perch weighs 200 g, then very large perches can be found in this reservoir. The above considerations are equally valid for all types of fish. The growth rates of some fish in the most favorable water bodies are indicated in table 2.

The age of a fish is determined by its scales. As the fish grows, the size of each scale also increases due to the appearance of new, young, large scales from below, i.e., as the age of the fish increases, the scales increase in thickness and consist, as it were, of a stack of plates superimposed on each other, of which the top one is the oldest and small, and the bottom one is the largest and youngest.

If you examine the scales through a magnifying glass with 8-10x magnification, you can see a number of concentric rings corresponding to the edges of all the gradually formed plates (Fig. 4).

But the growth of the fish, and with it the scales, is uneven throughout the year. In summer, fish grow quickly, and the distances between the edges of the plates appearing from below are greatest. In autumn, due to slower growth, these distances decrease, and by winter the edges come so close that one dark ring is formed. In winter, the fish does not grow, and in summer, new concentric circles appear on its scales, which by autumn merge and give a new dark ring. The number of dark rings on the fish’s scales will correspond to the number of years of its life.

Instinct and experience.

Some fishermen attribute exceptional intelligence to fish, telling “hunting” stories about pikes and ides opening the lids of cages, about bream rising through the forest to the surface of the water so that, once convinced of the presence of an angler, they disappear into the depths, about “smart” carp, knocking down with their tail bait from the hook and only after that feast on it; about “cunning” perches driving away their less intelligent comrades from a hook with a nozzle, etc.

Of course, most of these stories are a figment of the imagination of those telling them, but there are examples that seem to confirm the presence of “smartness” in fish. Don’t the long journeys of salmon, whitefish, and eels in search of favorable spawning places seem smart? Or the protection of offspring observed in stickleback, catfish and some other fish? Or the method of obtaining food used by the tropical spray fish, which, releasing a stream of water from its mouth, knocks insects from the trees surrounding the pond and grabs them as they fall? The behavior of the fish, clearly wary of thick and rough forests, also seems intelligent.

Academician I.P. Pavlov believes that fish, like land animals, have two types of activity that seem to replace reason: based on individual experience and instinctive, passed on from generation to generation. These two types of activity explain the actions of fish that seem smart to us.

Spawning migrations, protection of offspring, one or another method of obtaining food are instinctive actions developed in fish in the process of adaptation to changing living conditions. The suspicious attitude of fish towards unfamiliar objects or towards familiar objects that behave unusually is explained by the instinctive caution of fish, developed due to the need to constantly fear enemies, as well as personal experience acquired by this individual.

The role of skills in the actions of fish is clearly illustrated by the following example. The aquarium with the pike in it was partitioned with glass and a live fish was allowed into the fenced off part. The pike immediately rushed towards the fish, but after hitting the glass several times, it stopped its unsuccessful attempts. When the glass was taken out, the pike, taught by “bitter” experience, no longer renewed attempts to grab the fish. In the same way, a fish that has been hooked or grabbed an inedible spoon takes the bait much more carefully. Therefore, in remote reservoirs, where fish are unfamiliar with people and fishing rods, they are less careful than in reservoirs frequently visited by fishermen.

In order for a fish to become wary of rough tackle, it does not have to be hooked itself. Sharp throws of one frightened, hooked fish can frighten and alert the entire flock for a long time, causing a suspicious attitude towards the proposed bait.

Sometimes fish use the experience acquired by their neighbor. In this regard, the behavior of a school of bream surrounded by a seine is characteristic. First, finding themselves in the tone, the bream rush in all directions; but as soon as one of them, taking advantage of the unevenness of the bottom, slips under the bowstring, the whole flock immediately rushes after him.

Since the caution of a fish is directly related to the experience it has acquired, the older the fish, the more suspicious it is of all kinds of unfamiliar objects. In different species of fish, caution is developed differently. The most cautious species include carp, bream, trout, and ide; the least cautious species include perch, burbot, and pike.

The gregarious lifestyle plays a big role. It is easier for a flock to escape from enemies, find food and places convenient for breeding.

Thus, the “wit,” “intelligence,” and “cunning” of fish are explained by the existence of innate instinct and acquired experience. Instinctively, the fish is afraid of swinging the rod, shaking the soil, splashing in the water, it avoids thick and rough fishing line, a hook that is not disguised by the bait, etc. This means that the fisherman must be able to disguise his tackle, be careful and observant.

Pisces class- this is the largest group of modern vertebrates, which unites more than 25 thousand species. Fish are inhabitants of the aquatic environment; they breathe through gills and move with the help of fins. Fish are distributed in different parts of the planet: from high mountain reservoirs to ocean depths, from polar waters to equatorial ones. These animals inhabit the salty waters of the seas and are found in brackish lagoons and the mouths of large rivers. They live in freshwater rivers, streams, lakes and swamps.

External structure of fish

The main elements of the external body structure of a fish are: head, operculum, pectoral fin, ventral fin, body, dorsal fins, lateral line, caudal fin, tail and anal fin, this can be seen in the figure below.

Internal structure of fish

Fish organ systems
	1. Skull (consists of the braincase, jaws, gill arches and gill covers) 2. Skeleton of the body (consists of vertebrae with arches and ribs) 3. Skeleton of fins (paired - pectoral and abdominal, unpaired - dorsal, anal, caudal)	1. Brain protection, food capture, gill protection 2. Protection of internal organs 3. Movement, maintaining balance
Musculature	Wide muscle bands divided into segments	Movement
Nervous system	1. Brain (divisions - forebrain, middle, medulla oblongata, cerebellum) 2. Spinal cord (along the spine)	1. Movement control, unconditioned and conditioned reflexes 2. Implementation of the simplest reflexes, conduction of nerve impulses 3. Perception and conduction of signals
Sense organs	3. Hearing organ 4. Touch and taste cells (on the body) 5. Lateral line	2. Smell 4. Touch, taste 5. Feeling the direction and strength of the current, the depth of immersion
Digestive system	1. Digestive tract (mouth, pharynx, esophagus, stomach, intestines, anus) 2. Digestive glands (pancreas, liver)	1. Capturing, chopping, moving food 2. secretion of juices that promote food digestion
swim bladder	Filled with a mixture of gases	Adjusts immersion depth
Respiratory system	Gill filaments and gill arches	Carry out gas exchange
Circulatory system (closed)	Heart (two-chambered) Arteries Capillaries	Supplying all body cells with oxygen and nutrients, removing waste products
Excretory system	Kidneys (two), ureters, bladder	Isolation of decomposition products
Reproduction system	Females have two ovaries and oviducts; In males: testes (two) and vas deferens

The figure below shows the main systems of the internal structure of fish

Fish class classification

Living fish today are divided into two main classes: cartilaginous fish and bony fish. Important distinguishing features of cartilaginous fish are the presence of an internal cartilaginous skeleton, several pairs of gill slits that open outward, and the absence of a swim bladder. Almost all modern cartilaginous fish live in the seas. Among them, the most common are sharks and rays.

The vast majority of modern fish belong to the class of bony fish. Representatives of this class have an ossified internal skeleton. A pair of external gill slits are covered with gill covers. Many bony fish have a swim bladder.

Main orders of Pisces

Orders of fish	The main characteristics of the detachment	Representatives
	Cartilaginous skeleton, no swim bladder, no gill covers; predators	Tiger shark, whale shark, katran
	Manta ray, stingray
Sturgeon	Osteochondral skeleton, scales - five rows of large bone plates, between which there are small plates	Sturgeon, beluga, sterlet
Dipnoi	They have lungs and can breathe atmospheric air; the chord is preserved, there are no vertebral bodies	Australian cattail, African scalefish
lobe-finned	The skeleton mainly consists of cartilage, there is a notochord; poorly developed swim bladder, fins in the form of fleshy outgrowths of the body	Coelacanth (the only representative)
Carp-like	Mostly freshwater fish, there are no teeth on the jaws, but there are pharyngeal teeth for grinding food	Carp, crucian carp, roach, bream
Herring	Most are schooling sea fish	Herring, sardine, sprat
cod	A distinctive feature is the presence of a mustache on the chin; the majority are cold-water marine fish	Haddock, herring, navaga, burbot, cod

Ecological groups of fish

Depending on their habitat, ecological groups of fish are distinguished: freshwater, anadromous, brackish and marine.

Ecological groups of fish	Main features
Freshwater fish	These fish constantly live in fresh water. Some, such as crucian carp and tench, prefer standing water. Others, such as the common gudgeon, grayling, and chub, have adapted to life in the flowing waters of rivers.
Migratory fish	This includes fish that move from sea water to fresh water to reproduce (for example, salmon and sturgeon) or from fresh water to breed in salt water (some types of eels)
Salty fish	They inhabit desalinated areas of the seas and the mouths of large rivers: such are many whitefish, roach, goby, and river flounder.
Sea fish	They live in the salty water of seas and oceans. The water column is inhabited by fish such as anchovy, mackerel, and tuna. Stingrays and flounder live near the bottom.

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A source of information: Biology in tables and diagrams./ Edition 2, - St. Petersburg: 2004.

Size and growth of fish. The sizes of fish vary significantly and are specific to each species. The smallest fish, tiny gobies that inhabit the waters of the Philippine Islands, reach sexual maturity with a body length of 7.5-14 mm. Some representatives of oceanic sharks reach a length of more than 20 m and a mass of 15 tons (whale shark), a giant shark reaches a length of 15 m and a weight of 4 tons. Of the commercial fish of inland waters, the largest fish are sturgeon - beluga and kaluga, the length of which sometimes exceeds 4 m , weight - 1 t.

Fish growth is an increase in its biological indicators over a certain period of time. In fish, a distinction is made between linear growth (increase in body length) and growth in body weight.

Body weight growth is more susceptible to fluctuations depending on nutritional conditions than linear growth. In pond fish farming, the main indicator of the efficiency of fish farming is the increase in body weight of the fish.

A feature of fish is constant growth, which does not stop throughout life. Fish grow unevenly throughout their lives. Fish usually grow faster before they reach sexual maturity. Food is used mainly for linear growth (producing food). Therefore, in the first years of life, linear dimensions increase most rapidly. After the onset of puberty, the rate of linear growth decreases, and weight gain often even increases. A significant part of the food consumed is spent on the formation of reproductive products and reserve substances for migration, wintering, etc. The share of producing food decreases, the share of supporting food increases (to support the vital functions of the body). During the aging period of the body, linear growth slows down significantly, food is spent mainly on maintaining life processes.

In most fish, males grow slower than females.

Fish growth is uneven throughout the year. For inhabitants of the northern and southern hemispheres, a rapid growth rate of fish is characteristic of a period of intensive feeding, which corresponds to the warm period of the year; a slowdown (or cessation) of growth occurs in the winter.

The growth rate of fish is significantly influenced by environmental conditions (temperature, light, gas conditions, population density of the reservoir, food resources, etc.). Each type of fish is characterized by optimal temperatures at which the metabolic process occurs most intensively. The quantity and availability of food are of great importance for fish growth. The growth of fish of the same species in different bodies of water, its individual populations and different generations of the same population can vary significantly. Thus, bream in northern reservoirs grows much slower than in the south, where the feeding period is longer. The growth rate of bream is significantly different in the Azov and Caspian Seas, since food resources in the Azov Sea are better.

At the same time, the growth rate of fish in the same body of water can vary significantly depending on many factors (hydrological conditions, quantity and quality of food, as well as the size of the population or individual generations of fish).

The growth rate changes sharply due to changes in living conditions and the feeding patterns of fish. Thus, in the first years of life in the river, Atlantic salmon feeds mainly on insect larvae and grows very slowly. Having rolled into the sea, salmon switches to feeding on fish and sharply increases its growth rate.

When nutritional conditions deteriorate, there is not only a slowdown in growth, but also an increase in growth variability, so individuals of the same age end up with individuals of different sizes. This difference in growth allows for more complete use of the food resources of water bodies. Small and large individuals have different nutritional spectrums. As nutritional conditions improve, fish growth levels out and the fish switch to feeding on similar food.

An important factor influencing growth is fishing, which can reduce population numbers and create better conditions for feeding uncaught fish, which leads to an increase in growth rate. Overpopulation of water bodies with fish can lead to a decrease in their growth rate.

Various diseases also affect the growth rate of fish.

Lifespan of fish. The lifespan of fish varies. Some species inhabiting the fresh waters of Africa and South America live for several months and reach sexual maturity already in the 2-3rd month of life (afiosemion, tsinolebia, etc.), the age of some sturgeon fish can reach 100 years (beluga and kaluga )

Most small-sized fish have a short life cycle of 2-3 years (anchovy, Azov sprat, three-spined stickleback, etc.). The usual age of long-livers is 20-30 years (pike, carp, catfish, halibut, etc.).

Natural life expectancy is determined by the species' metabolic characteristics. Some species die after the first spawning (pink salmon, river eel, etc.).

Under the influence of various factors and intensive fishing, fish do not reach their age limit. Therefore, in unfished water bodies, fish populations may include large numbers of older fish.

There are various methods for determining age. In most fish, age is determined by their scales. Sclerites are formed on the integumentary layer of scales. During periods of intensive fish growth, the width of the sclerites and the distance between them are wide; during periods of slow growth, they are narrowed. The wide and narrow strips together constitute one annual zone.

In addition to annual rings, additional rings can form on fish scales: spawning marks (rings) as a result of partial destruction of the scales during spawning (Atlantic salmon, etc.), fry rings (in the first year of life) during the period of sharply changing habitat conditions of juveniles, during transition from plankton feeding to benthos feeding, etc. (roach, bream, etc.). Additional rings often have the appearance of a half ring or a ring with gaps.

When determining the age of fish by scales, it can be difficult to distinguish between annual and accessory rings, as well as to determine annual rings in fish of older age groups. In some species, the number of rings does not correspond to the number of years the fish has lived; for example, in the river eel, the formation of scales occurs in the 3-5th year of life.

The age of fish can also be determined by bones and otoliths. Layers form on the bones and otoliths of fish. Wide layers are formed during intensive growth of fish, narrow layers - when growth is slow. The narrow layer is mistaken for the annual ring.

To determine age, various bones are used: gill cover (perch), vertebrae (burbot, pike), fin rays (sturgeon, catfish, sharks), otoliths (smelt, ruff), etc.

The age structure of the population includes individuals of different age groups (Table 1). To determine it, the method of direct determination of the age of fish is used (the percentage of age groups in the sample is established).

Table 1

Determination of fish growth rate. For fisheries, data on long-term and seasonal growth of fish is of great importance, which can be determined by measuring groups of different ages, as well as by inversely calculating the growth rate.

Norwegian scientist Einar Lea noticed that scales increase with age in direct proportion to the length of the fish:

Ln/1 = Vn/V, i.e., l n = V n l/V,

where l is the length of the fish at the time of capture; V is the length of the scale from the center to its edge; l n is the calculated length of the fish at the age of n years; V n is the length of the scales from the center to the annual ring at the age of n full years.

By calculating the linear size of a fish for each year of its life, it is possible to determine the annual growth of its body. To do this, from the calculated length of the fish for the year in relation to which the increase l n is determined, the length characteristic of it in the previous year l n-1 is subtracted and the value of the increase t is obtained. Thus, t 1 - growth for the first year of life is equal to l 1 - the calculated length for the first year of life, and t 2 =l 2 -l 1; t 3 =l 3 -l 2 etc.

Subsequently, the method proposed by E. Lea was modified. It has been shown that in some fish there is not a direct, but a logarithmic relationship between the growth of the body and scales. The main reason that violates the proportionality between the length of the fish and the scales is that the scales on the body of the fry are laid only after it reaches a certain length and therefore the initial growth of the body is not represented on the scales. Special device G.N. Monastyrsky allows you to calculate growth using the logarithmic scale method.

When analyzing fish growth, various indicators are used. Usually calculated:

1) linear increase, or increase in body weight: W1-W 0 (Wi - final value, W 0 - initial value);

2) relative increase, or growth rate: (W 1 -W 0)/W 0 (W 1 - final value, W0 - initial value);

3) relative growth rate K (growth in a certain period of time):

K = W1-W0 / ((W1+W0)/2)t,

where W 0 is the size of the body at the beginning of the period; W 1 is the size of the body at the end of the period, t is the time period.

Knowledge of the age and growth characteristics of fish is a necessary condition when assessing the state of stocks of various fish species. An important indicator when developing fishing and fish farming methods is to determine the size and age of the fish, upon reaching which the growth rate begins to slow down.