Perches, like most fish, are dioecious. In females, in the body cavity there is a large ovary in which egg cells (eggs) develop, in males there is a pair of long testes. During the breeding season, the testes are filled with a thick white liquid - milk. Milk contains millions of sperm. The genitals open outward on the ventral side of the body through the genital opening.

Fish Spawning

When the reproductive cells mature, the reproductive instinct appears in fish. At this time, they move to places more favorable for the development of their offspring. Some species of fish rush from the sea to rivers, while others, on the contrary, leave rivers for the sea - these are the so-called migratory fish. They travel long distances to spawn.

The complex instinctive behavior of fish during the breeding season is called spawning.

On Far East The movement of some salmon (chum salmon, pink salmon) during spawning presents an interesting sight: huge schools of fish move upstream, overcoming all obstacles. At rapids, fish jump out of the water, and in shallow places they literally crawl along the bottom, exposing their backs to the air. In the upper reaches of rivers, fish lay eggs and, completely exhausted, slide downstream. Many of them die in the process. Migratory fish that constantly live in the sea and enter rivers to reproduce also include sturgeon and some other fish.

Eels, which have a long snake-like body, live in fresh water bodies, and to reproduce they leave the rivers of Europe and North America V Atlantic Ocean. Many fish breed in the shallow waters of their reservoirs.

Perch reaches maturity in the second year. Its spawning begins only after the disappearance of ice on reservoirs. Some time before spawning, the color of the perches becomes especially bright. They gather in flocks in creeks, oxbow lakes and other places that are shallow and without a current.

Females spawn eggs glued together in the form of ribbons onto aquatic plants. Males emit milk at this time. Motile sperm swim up to the eggs and penetrate them.

Fish development

The fertilized egg begins to divide. A multicellular embryo is formed, in which a yolk sac is visible on the ventral side - the remainder of the reserve nutrients caviar. In perch, 9-14 days after fertilization, the larva leaves the egg shell and soon begins to feed on its own, first with microorganisms, and then with small crustaceans and other animals suspended in the water column. After some time, the larva becomes similar to an adult perch - this whitebait. It grows relatively quickly: after about two months its body is 2 cm long, and after a year the young perch grows up to 10 cm.

Figure: development of river perch

Fish care for offspring

Perch eggs often die from drying out reservoirs, and larvae and fry die from enemies. Only due to the fact that during spawning a female perch spawns up to 300,000 eggs, some of the offspring survive to adulthood. The number of eggs in fish of other species may be even greater. For example, cod spawns several million of them.

Those species of fish that are characterized by caring for their offspring usually lay a few eggs, but their eggs, larvae and fry do not die in most cases.

Picture: Stickleback at the nest

The male three-spined stickleback builds a muff-shaped nest from algae and guards the eggs laid in the nest by the females. Having spread his spines, the male furiously attacks fish approaching the nest, clears it of debris and straightens it, and with the movement of his pectoral fins drives fresh water there. For several days he guards the fry and does not allow them to disperse far from the nest, thus preserving the young offspring.

Pattern: Males seahorse brooding eggs in a pouch on the belly

The care for offspring of the African freshwater fish tilapia is amazing: the male carries the eggs in the mouth, and the fry hide in the father’s mouth in case of danger. Male seahorses carry eggs in a pouch on their belly.

So, let's try to figure it out and understand how fish reproduce and develop. Let's start by understanding what instincts control it while it reproduces. An important instinct is the choice of place for spawning. By the way, spawning is scientifically called spawning. So, the fish chooses a place in which is easier for the offspring to survive. But it's not always easy to get there. For example, salmon have to overcome rapids. The poor fish, rising up the river, often spends all its vitality, so rarely does anyone return home. Less picky ones find quiet backwaters, and there they spawn, and a lot of them. One fish lays 1–2 thousand eggs.

Instincts

Some species of fish have another instinct: caring for their offspring. Here, during evolution, each species came up with its own way of courtship. But basically, they care for their offspring by building a nest. For example, Gourami makes a nest of air bubbles. The female lays eggs there, and then the pair guards this nest until the fry hatch. Why only until the fry stage? Simply because only a fry that cannot feed itself is considered defenseless. The presence of such an instinct depends on the method of spawning.

In total, there are three types of fish reproduction and development:

• Viviparity.
• Ovoviviparity.
• Oviposition.

Viviparity - with this method of reproduction, the fish simply does not need any nest. And there is no need to stay with caviar either. Since she stores the eggs, fertilized with the help of the male, in her own place, in the posterior section of the oviduct. During evolution a structure was formed there, which is similar to the mammalian placenta, with the help of which the mother feeds her offspring and raises them until the moment when the fry is considered independent, approximately 30-50 days.

Ovoviviparity - this method is similar to the previous one, but the mother fish does not have a placenta-like structure. However, the eggs also develop in the posterior section of the oviduct before hatching, and are also born almost as fry.

Oviposition - this is a common method of reproduction, the female lays eggs and the male fertilizes them. The eggs develop separately from their parents, so it was with this method of reproduction that the fish had to care for their eggs.

There are also species that incubate their eggs in the mouth, that is, as soon as the eggs are fertilized, the fish takes them into the mouth, and thus preserves them from predators. When the fry hatch from the eggs, the parent begins to periodically release them into the wild, and in case of even the slightest danger, a flock of fry swimming around the parent instantly hides in the fish's mouth.

But not everyone's eggs develop the same way. There are different cases:

• Parthenogenesis.
• Gynogenesis.
• Hermaphroditism.

Gynogenesis

To understand how fish reproduce and learn the characteristics of fish reproduction, let's look at some cases. Let's start with gynogenesis, this is the name for cases when eggs are fertilized with the help of males of a different species, but always close. That is, the sperm of a male of another species penetrates a female and fertilizes her, although without fusion of cell nuclei. Thus, of all the eggs that the female produces, not a single male will appear. This is rare, but it still happens in guppies and silver crucian carp.

Parthenogenesis

If the female spawned unfertilized eggs in the same clutch as the fertilized one, then this case will be called parthenogenesis. In this case, getting along with the fertilized eggs into the posterior section of the oviduct, the unfertilized caviar will not rot immediately, and therefore will not interfere with the fertilized one. In rare cases, these eggs develop, but only to the crushing stage, and in rare cases, even before the fry begins to hatch. The exception is the Issyk-Kul chebak; this fish easily obtains excellent offspring in this way.

Hermaphroditism

This is a gender change. This feature can occur once in a lifetime, or many times. The change occurs alternately, therefore self-fertilization does not occur. Inside the hermaphrodite fish there are gonads that act as both an oviduct and a testis. Thus, some in the course of life are both male and female.

Cyclicality

And also, fish are divided according to the number of spawnings: they can be monocyclic - once in a life, and polycyclic - many times in a life. Of course, the majority reproduce polycyclically, then the number of spawnings depends on life expectancy.

A few words about performance

As for the number of offspring, it depends on the species: if the fish is viviparous, then it will not fit and feed a large number of fry. Therefore, for each spawning, viviparous animals give birth to up to two hundred fry, no more. And after 30-50 days, up to two hundred fry are born again. But this period: 30-50 days is very average, that is, inaccurate.

If the fish lives in warm water, that is, 26−28 degrees, then the eggs inside develop faster. This means that instead of 50 days of development, it will take 40 days. Thus, viviparous women can give birth to quite a lot of fry. But it’s also worth talking about the death of the fry: it is reduced to a minimum, because the mother gives birth to fry that are almost able to swim and eat.

And now about egg-laying fish. They can produce up to a thousand eggs in one spawning. This is justified by the fact that a lot of eggs and fry die before they have time to grow. And also, for oviparous fish, no more than 30 days pass between spawnings.

Some oviparous mothers care for their young. And therefore between their spawnings it takes almost 2 times more days. And also, in fish that take care of their offspring, no more than a hundred fry are hatched in one spawning. Since it is impossible for two fish to look after all the fry if there are more than a hundred of them. But all the fry survive.

Conclusion

In conclusion, we can say that nature has come up with many ways of reproduction for fish alone, and this once again confirms the great diversity of life on Earth.

Fish, which inhabit almost all types of water bodies, are characterized by the greatest variety of reproduction methods among animals. Over a huge period - more than 400 million years, fish have mastered reservoirs with fresh and salt water, they live at various depths, in high-mountain and underground reservoirs, in rivers and streams with fast current and in stagnant silted floodplains and swamps. The environment and living conditions require adaptation for the survival of not only adult individuals, but also for maximum preservation of offspring. From this point of view, it is very interesting to get acquainted with the facts of how fish reproduce and what this gave to each species.

Classification of fish according to breeding conditions

Most fish species produce reproductive cells during external environment, and fertilization, as well further development they occur outside the female's body. The majority of species do not take care of their offspring, and some even eat larvae and fry. But they choose places for spawning, which are often vast distances from their usual habitat.

There are species of fish in which the parental instinct is highly developed. They build special nests for fertilized eggs, take care of and protect the territory. Some fish bear their offspring inside the body or on its surface, in the mouth. Moreover, both females and males take care of the offspring.

According to Kryzhanovsky S.G.

According to the classification of Professor S.G. Kryzhanovsky, adaptive features in fish are observed in early period development. The habitat is different not only for various types fish, but also at different stages of life. Fish breed in certain seasons and choose the most suitable ones for spawning. suitable areas reservoirs. Changes in the environment cause:

• fish fertility;
• type of fertilization and type of development of offspring;
• peculiarity of sexual cycles;
• distribution and migration;
• the possibility of relocating to reservoirs with a different hydrological regime during spawning.

According to the localization of the masonry, S.G. Kryzhanovsky divided all types of spawning fish into:

• pelagophilic - spawning in water;
• lithophilous - laying eggs on stones;
• phytophilous - on plants;
• psammophilous - on sand;
• ostracophilous - into the gills of bivalve mollusks;
• protecting their eggs.

This classification has been used in ichthyology for more than 170 years. 50 years after Kryzhanovsky’s classification, the famous ichthyologist Balon compiled his own classification, more detailed, which indicates not only the location of the laying, but also the types of nests being built, the type of egg laying on a substrate and without a substrate, a detailed analysis viviparous species fish

According to Balon

The eggs of some fish are able to swim both in the thickness and on the surface of the water, being in a state of lack of oxygen, and in some fish the eggs are able to be in diapause and remain viable without water. The laid eggs can be located above the surface of the water - on coastal stones or plants, and the male periodically pours water over them so that the shell does not dry out.

The types of nests that fish build are also very interesting:

• from foam;
• from a mixed substrate and material;
• glued sockets;
• from plants and their remains;
• from sand;
• on the surface of soil and stones, as well as in crevices and cracks;
• under the protection of sea anemones.

The adaptive features of fish that externally bear their offspring are striking. Depending on the location, there are the following types fish:

• moving their brood. They carry eggs in body cavities or on any part of it;
• bearing on accessory organs. They glue sticky eggs between the fins, on the skin. The female curls herself into a ring around her eggs;
• bearing eggs in the oral cavity. Growing larvae can feed from the yolk sacs or immediately after hatching they can emerge and feed outside;
• gestating in the brood chamber or in the gill slits.

Viviparous fish also carry fertilized eggs. Internal gestation can be with complete or incomplete transformation. When incomplete, the fish lay zygotes - eggs, at a certain stage of development. When fully metamorphosed, the female gives birth to fully formed fry.

Reproduction

The predominant method of fish reproduction is sexual, in which different-sex individuals of the same species participate in fertilization. Along with sexual ones there are:

1. Parthenogenesis– in which the development of the egg occurs without the fusion of male and female gametes. In some species, the development of germ cells goes through only the cleavage stage without the formation of a larva. Only in some cases do metamorphoses occur before the larval stage. In most cases, such offspring die. In salmon, fertilized and unfertilized eggs can coexist in one clutch.
2. Gynogenesis– reproduction, in which the germ cells of closely related fish species penetrate the eggs, but do not fertilize, but stimulate their development. As a result of gynogenesis, only female eggs emerge from the eggs. In Mexico, there are populations of mollies consisting only of females.

Most fish have male and female individuals (different sexes), but there are also hermaphrodites that combine the sexual characteristics of both sexes. In some species, sex changes occur with age. For example, in the red pagella, the ovaries begin to function as testes with age. In hermaphrodite guppies, ichthyologists have discovered the ability to self-fertilize, but the eggs are released unfertilized.

There are also differences in the method of fertilization. Highlight:

• external– in which fertilization of eggs by sperm occurs in the external environment;
• internal- when the male, using a pseudophallus, introduces seed into reproductive system females, where fertilization occurs.

In the latter case, the development of eggs occurs inside the female’s body, and fry are born, which immediately begin to feed on their own. Such fish are classified as ovoviviparous. In addition to ovoviviparous fish, there are also viviparous fish. In them, the lower parts of the oviduct form an analogue of the mammalian placenta. These include some species of sharks. In them, the nutrition of the larvae and fry is provided by the female’s body, and not by the yolk sac of the egg.

Depending on the nature of reproduction, all fish are classified into:

• monocyclic– representatives who spawn only once in their life, after which they die;
• polycyclic– laying eggs or giving birth to offspring throughout the entire period of life. These include most types of fish.

Great importance in the life activity and reproduction of fish has the speed of their sexual maturation and productivity.

Timing of puberty

In fish, puberty occurs in different periods life. The shorter a fish lives, the earlier it begins to reproduce. The variability of puberty ranges from 1-2 months to 15-30 years. Males mature earlier than females. The ability to procreate depends on the size of the individual. The better the fish eats, the faster it grows, the earlier it is able to spawn.

The metabolism of fish, and therefore life expectancy, is affected by water temperature. The higher it is, the faster the fish ages and the earlier it begins to spawn. Sexual dimorphism - visual differences between representatives of different sexes - plays a great role in creating a pair and successful fertilization. In some species it is difficult to distinguish females from males. In others, males have:

• larger size;
• more variegated, contrasting color;
• external genitalia - gonopodium or pterygopodia.

Sex differences may be present throughout life or appear only during the spawning period. Such " wedding attire", which occurs under the influence of activation of sex hormones, is typical for carp, whitefish, stickleback, salmon, and pink salmon.

Sex ratio and spawning characteristics

As a rule, in a population the ratio of females to males is 1:1. But under the influence of changing conditions it can shift in one direction or another. For example, infection of guuppies with the saprolegnia fungus leads to the death of the fish. In this case, the surviving females turn into males. Heat environment leads to a predominance of males in the green swordtail population. Stimulating the mark with steroids can also shift the sex ratio.

Among the fish there are:

• monogamous species– in which fertilization of the female’s eggs occurs only by one male;
• polygamous species– when there are 3-4 individuals of the opposite sex per individual.

The mark period is influenced by external and internal factors. Most often this is the temperature of the water in the reservoir. Each type of fish has its own comfort temperature regime, so spawning can occur in spring, summer or autumn. Caviar can ripen either simultaneously or in portions.

The time of spawning also varies - from a few seconds (stickleback) to several months (cod, plume). The same view in different conditions can lay eggs simultaneously or in portions. This adaptive mechanism helps to make maximum use of the food supply, increase the survival rate of young animals and the fertility of females.

Natural selection ensured the best survival and prevalence of populations, depending on living conditions. Maximum adaptation to these changes is provided by various ways reproduction. They allow you to survive the largest number juveniles, expand their range and compete with other species of inhabitants of the Earth’s water basins.

Reproduction and development of fish

The development of an organism is a set of quantitative and qualitative changes as a result of the interaction of the organism with the environment. IN individual development fish, we can distinguish a number of large segments – periods, each of which is characterized by common different types properties.

I. Embryonic period - from the moment of fertilization of the egg until the transition of the juveniles to external power supply. The embryo is nourished by the yolk, a supply of food received from the mother's body. This period is divided into two sub-periods:

1) the sub-period of the egg, or the embryo itself, when development occurs in the shell;

2) the subperiod of the free embryo (prelarva), when development occurs outside the shell.

II. The larval period begins from the moment of transition to feeding on external food; appearance And internal structure have not yet taken on the forms of an adult organism. The larvae have specific larval organs, which subsequently disappear.

III. Juvenile period - the appearance is close to the appearance of an adult organism. Larval organs disappear, and organs and functions characteristic of adults appear. The genitals are almost undeveloped. Energy resources are consumed mainly by growth. Secondary sexual characteristics are usually absent.

IV. The period of a semi-adult (immature) organism: the development of the gonads and secondary sexual characteristics begins, more or less, but the organism is not yet capable of reproduction.

V. The period of an adult (sexually mature organism) is a state in which, at a certain period of the year, the organism is able to reproduce its own kind; secondary sexual characteristics, if they are characteristic this species, are available. Energy is wasted predominantly. For the development of the reproductive system and the creation of reserves to maintain vital functions during migration, wintering, and reproduction.

VI. The period of old age - sexual function fades; growth in length stops or slows down extremely.

Within a subperiod or period, stages are distinguished. The theory of the stages of fish development was developed by domestic scientists from the school of Academician A. N. Severtsov, S. G. Kryzhanovsky and V. V. Vasnetsov. At each stage, the organism is characterized by specific adaptations to the environment, i.e., certain features of structure, respiration, nutrition, and growth. During the stage, the organism grows, but significant changes in its structure and relationships with the environment do not occur. In this case, properties are developed that ensure the transition to the next stage. Stage means any this moment development.

Reproduction is the most important life process that ensures the existence of a species. IN organic world Reproduction can occur in two ways - asexual and sexual.

Pisces tend to sexual reproduction, although in many species of herring, sturgeon, salmon, carp and some others, mature germ cells, once in the water, begin to develop parthenogenetically, that is, without fertilization. In this case, as a rule, development reaches only the stage of fragmentation and only in exceptional cases Viable larvae were obtained that lived until complete resorption yolk sac(herring, Sakhalin herring, burbot, chebachok, perch).

Some fish species (goldfish Carassius auratusgibelio, Molinisia formosa) are completely unusual way reproduction - gynogenesis. In many areas of the range, populations of these species consist only of females (males are absent or single and sexually inferior). In such same-sex populations, females spawn with the participation of males of other species. With this type of reproduction, the penetration of sperm into the egg is a necessary condition development. However, the fusion of the sperm and egg nuclei does not occur and the egg nucleus becomes the nucleus of the zygote (the sperm nucleus is genetically inactivated). As a result, only females appear in the offspring without external signs those males who took part in spawning. The cytogenetic basis of this process is triploidy of females from same-sex populations (with a specific course of maturation divisions).

The reproduction and development of fish differ in a number of specific features due to by water life.

In most fish, insemination is external. Unlike terrestrial animals, mature reproductive cells of fish are released into the water, where fertilization of eggs and their further development occur. Insemination, fertilization and incubation of eggs in water, outside the mother's body, entails greater death of the offspring in the early stages of development. To ensure the preservation of the species in the process of evolution, fish have developed either greater fertility or care for their offspring.

The fertility of fish is much higher than that of terrestrial vertebrates. This is an adaptive property of a species to the conditions of existence. Number of eggs laid different types, varies greatly - from a few pieces in the polar shark to 200 million in the sea pike and 300 million in the sunfish. The most prolific fish are those that lay floating pelagic eggs; followed by fish, whose eggs develop glued to plants. Fish that hide or protect their eggs have low fertility.

There is an inverse relationship between individual fecundity and the size of eggs: in fish with large eggs it is lower, in fish with small eggs it is higher (in chum salmon the egg diameter is 7–8 mm, fecundity is 2–4 thousand pieces, in cod the egg diameter is 1.1–1, 7 mm, fertility up to 10 million pieces).

The supply of fish with food has the strongest influence on fertility. In fish of the same size, fertility is significantly higher in favorable conditions feeding - in feeding years, in sparse populations. In addition, within the same species, fertility depends on the size and age of the fish. Fertility in one and the same individual is different equal conditions– with growth, it first increases, then decreases with old age, despite the continuing absolute growth.

There are individual, relative and working fertility. Individual, or absolute, or general, fertility is total eggs laid by a female during one spawning period under favorable conditions. For example, for a 6-year-old carp it averages about 900 thousand pieces. Relative fecundity is the amount of eggs per unit body weight of the female; carp has 180 thousand pieces/kg body weight; this indicator is especially convenient for comparison; it clearly shows how the amount of caviar changes with the growth of the fish: up to a certain age it increases, then decreases. Working fertility is the amount of eggs obtained from one female during artificial insemination in fish farming practice. To determine fertility, a sample of eggs is taken at the stage of its greatest development, i.e. shortly before spawning.

The onset of sexual maturity in different species occurs at at different ages, and in many cases males mature a year earlier than females. The most early ripening commercial fish, with short life cycle(some gobies, Caspian sprat, anchovy, smelt), mature at one year of age. Fish with a long life cycle, such as sturgeon, become sexually mature at 7–8 (stellate sturgeon), 12–13 (sturgeon) and even 18–20 years (beluga and kaluga).

In fish of the same species, maturity can occur at different ages, depending primarily on the rearing temperature and the availability of food. Carp in middle lane matures at the age of 4-5 years, in the southern regions - at 2 years and then spawns once a year, in the tropics - in Cuba - at the age of 6-9 months and spawns at six-month intervals. In fish of the same species, the rhythm of sexual maturation in the tropics is different than in the middle zone (Fig. 33). Typically, the time of puberty is associated with the individual reaching a certain size. The slower the fish grows, the later it matures. The sex ratio varies among species, but most are close to 1:1, except those that exhibit gynogenesis.

Rice. 33. The rhythm of the sexual cycles of fish (carp) at different latitudes.

A – in the tropics; B–c temperate zone(according to Privezentsev, 1981):

1 – I stage, 2 – II, 3 – III, 4 – IV, 5 – V, 6 – VI stage

Most fish do not have secondary sexual characteristics, so females and males do not differ in appearance. However, sexual dimorphism is manifested in different sizes of females and males: among fish of the same age, females are larger than males, with the exception of some species - capelin, sockeye salmon, and channel catfish. However, in many fish, sexual dimorphism becomes noticeable in the pre-spawning period, during maturation, when the so-called nuptial plumage appears - in the vast majority of cases in males. In carp and whitefish, a pearly rash forms on the head and body, in grayling the fins turn red, in loaches bright spots appear on the body, in salmon the jaws change and a hump appears (sockeye salmon, pink salmon), purple spots appear along the body (chum salmon), etc. After spawning, the nuptial plumage disappears, however, for example, Far Eastern salmon, eels, blackback herring, the changes in the body are so strong and irreversible that after the first spawning the fish die. In some species of our fauna, secondary sexual characteristics are quite clearly expressed.

They are manifested in most cases in the size of the fins: in some catfish, the gudgeon Gobio gobio, the Baikal yellowfly Cottocomephorus grewingkii, pectoral fins males have more than females; male tenches Tinca tinca have larger pelvic fins and their second rays are thicker; Male grayling Thymallus thymallus and four-horned sculpin Myoxocephalus quadricornis have longer dorsal fins. In polar flounders of the genus Liopsetta, males have ctenoid scales, and females have cycloid scales. Some deep sea fish(Ceratiidae) small males grow attached to the female’s body.

Pre-spawning changes in Rhodeinae bitterlings, which lay eggs in the mantle cavity, are very peculiar. bivalves: in males the color becomes very bright, and in females a long ovipositor grows.

According to the timing of spawning, fish of our fauna are divided into:

a) spring-spawning (herring, rainbow trout, pike, perch, roach, orph);

b) summer-spawning (carp, carp, tench, rudd);

c) autumn-winter spawning (many salmon, whitefish, burbot, navaga).

This division is to a certain extent arbitrary—one and the same species in different areas spawns in different time: carp spawns in the middle zone in May–June, on the islands of Java and Cuba - all year round.

Spawning time varies greatly throughout the day: salmon, burbot, and anchovy usually spawn at night, anchovy in the evening, carp spawn most often6; at dawn.

Changes in the gonads of fish throughout the year (annual sexual cycles) follow the same pattern. However, different species have characteristics in maturation and, above all, in the duration of different stages of maturity.

Based on the duration of the spawning period, two groups of fish are distinguished: with one-time and batch spawning. In simultaneous spawning fish, eggs are laid immediately, at the same time: in short term(one morning) roach and perch spawn. Many tropical fish spawn within an hour. All caviar of such fish, intended for removal in this season, ripens immediately and is completely swept out.

Other fish lay eggs in several stages, in separate portions, at intervals of 7–10 days. Typical representative– Caspian herring. In their gonads, the eggs mature and are released in successive portions. As a result, individual fertility increases: with batch spawning, the female spawns 2–3 times during the season more caviar than with a one-time

Portioned spawning is typical mainly for fish of the tropics and subtropics, in temperate latitudes There are fewer of them, almost none in the Arctic.

There are fish that, although they do not have a pronounced portioned spawning, their spawning period (for one individual) stretches for several days, i.e. the eggs are also spawned in several stages (bream, sometimes carp). Some fish in the southern part of their range spawn in portions, in the northern part - at once (bream, carp).

Portioned spawning helps to increase the fertility of fish and the provision of food for offspring, as well as better survival of juveniles in unfavorable conditions a habitat. For example, in reservoirs with fluctuating levels, significantly more types fish with portioned spawning.

The spawned eggs of the vast majority of fish are spherical, but there are also oval (anchovy), cigar-shaped (gobies, rotan) and even teardrop-shaped and cylindrical (some gobies). The color of the eggs in most species is yellowish, orange in different shades, in sturgeon it is black, in gobies it is green. The yellowish and orange color is due to the presence of carotenoids. The size of the eggs varies greatly: in some herrings and flounders the eggs are less than 1 mm in diameter, in sharks - up to 8-9 cm and higher, and they increase as the species moves north and to depths.

Size of eggs, mm

Frilled shark Chlamydoselachus anguineus 90 – 97

Brook trout Salmo trutta morpha fario 4.0 – 6.5

Black Sea sprat Sprattus sprattus 0.9 – 1.15

Blackback herring Caspialosa kessleri 2.87 – 3.93

Carp Cyprinus carpio 0.9 – 1.5

Tench Tinca tinca 1.0 – 1.2

Chekhon Pelecus cultratus 3.8 – 5.9

River flounder Pleuronectes flesus 0.78 – 1.3

Perch Perca fluviatilis 2.0 – 2.5

Pike-perch Lucioperca lucioperca 1.2 – 1.4

Pike Esox lucius 2.5 – 3.0

Eggs, spawned and developing in different environmental conditions, have a number of features that contribute to their adaptability to the environment (Fig. 34). Floating, or pelagic, eggs develop in the water column; bottom or demersal eggs develop on the bottom or on the substrate.

Rice. 34. Eggs developing in different environmental conditions (not to scale).

A, B – sharks and rays (according to Nikolsky, 1971); pelagic: V – anchovy, G – sabrefish, D – snakehead;

bottom: E – whitefish, F – trout; attached: Z – saury, I – silverside

In pelagic eggs developing in the water column, an increase in buoyancy is ensured by a number of adaptations. These include: hydration of the yolk (in sea pelagic eggs the water content reaches 85–97%, making them lighter sea ​​water, while in the bottom - up to 60–76%), an increase in the perivitelline space due to the presence of fat drops in the yolk (many herring, flounder) or the formation of outgrowths that facilitate the retention of eggs in the water column (saury, etc.).

In sabrefish, Far Eastern herbivorous fish, and anadromous herring, the eggs are semi-pelagic; they develop in the water column, on a current, in a river, but in stagnant water they drown.

Eggs laid on a substrate (vegetating or dead plants, stones, driftwood, etc.) often have sticky shells (sturgeon, Atlantic and Pacific herring, carp, crucian carp, fisherman, etc.) or are equipped with thread-like or hook-shaped processes , with which they are attached to the substrate. The eggs are often laid compactly, and the clutches have characteristic shape. For example, in perch, the eggs are surrounded by a viscous gelatinous substance, and the clutches look like long (2–3 m) ribbons (Fig. 35). However, they may not attach to the substrate (salmon, burbot). Bottom eggs are characteristic of the vast majority freshwater fish or marine, spawning in coastal zone. The amount of yolk and plasma in the eggs of different fish species is not the same. Based on their ratio, bony fish eggs are divided into oligoplasmic (containing little plasma and a lot of yolk) and polyplasmic (rich in plasma and poor in yolk).

Rice. 35. Laying of eggs of Pacific herring (A), carp (B), rotan (C), perch (D)

The reserve material for the nutrition of the embryo - the yolk of the oocyte - consists mainly of proteins, the bulk of which are represented by lipophosphoproteins (ichthulin) and not big amount albumin, and lipids (mainly phosphatides, primarily lecithin, and also cholesterol); there is a small amount of polysaccharides and neutral fats.

In many fish, the cytoplasm of the oocyte contains fat droplets, consisting mainly of neutral fats - glycerides. Fish eggs are characterized by a large amount of water. The protein content in them varies greatly (from 12–14 to 29–30% of wet weight) and fats (from 1–2 to 22% wet weight). In this case, the amount of proteins prevails over; the amount of fat (the protein/fat ratio, for example, in peled is 1.17, in trout - 3.25, in carp - 4.15, and in pike and pike perch - 21.19–21.66).

The calorie content of caviar also varies, for example, sturgeon and salmon have 25,522–25,941 J/g, and mullet have 16,318 J/g of dry matter. The carbohydrate content in fish eggs is insignificant: lumps of glycogen were found (cytochemically) in sturgeon, salmon, peled, and carp.

Thus, the main source of energy during the development of the embryo is proteins, which cover up to 70% of the energy consumed. Fats, unlike bird egg fats, are consumed to a lesser extent. At the same time, in pelagic eggs the reserve of energy substances is less, in benthic eggs it is greater.

A mature sperm is a cell with a small amount of plasma. It distinguishes the head, middle part and tail (Fig. 36). The shape of the head is different: in the form of a ball, an egg, an acorn (in most bony fishes), sticks (in sturgeons and some bony fishes), a spear (in lungfishes), a cylinder (in sharks, lobe-finned fishes). The head houses the core. An acrosome is located in front of the nucleus in sharks, sturgeons and some other fish; Teleosts do not have acrosomes. The nuclear part of the sperm head consists mainly of deoxyribonucleoprotein (neutral salt of DNA with the main protein - protamine) and small amount RNA. The DNA concentration in the head (nucleus) is 38.1% (carp), 48.4% (salmon) and reflects the amount of DNA in the haploid set of chromosomes. Protamines consist of 6–8 amino acids, among which arginine predominates. Mitochondria are found in the middle part of the sperm, which play a major role in supplying the cell with energy. Proteins, lecithin, fats and cholesterol were identified in the tail part. The spermatozoa of most teleost fish have a total length of 40–60 µm (head 2–3 µm).

Rice. 36. Fish sperm.

A – bony; B – sturgeon (according to Ginzburg, 1968):

1 – crucian carp, 2 – pike, 3 – goby Gobius niger,

4 – sculpin Cottidae (view of the head from the flattened side and from the side);

a – acrosome, d – head together with the middle part,

hch – main part, kch – end part of the tail

The sperm secreted by the male consists of sperm immersed in sperm fluid, similar in composition to saline. At the moment of leaving the body, sperm are still motionless, their metabolism is reduced.

In one and the same male, spermatozoa are qualitatively different. First of all, they differ in size: in the ejaculate, using centrifugation, three groups of sperm can be distinguished - small (light), large (heavy), intermediate (medium). They also differ in biological properties, in particular by the nature of the gametes: among large spermatozoa there are large numbers of X-gametes, among small ones - Y-gametes. As a result, from eggs fertilized by large spermatozoa, predominantly females are born, and from small spermatozoa, males are born.

These data are used to develop targeted sex formation in fish, which is important in fish farming. The amount of sperm that a male simultaneously releases during spawning and the concentration of ejaculates vary among different species (Table 6). It depends on a complex of internal and external factors: size, age and condition of males, spawning conditions - currents, temperature, ratio of females and males on spawning grounds, etc.

In sperm fluid, sperm are immobile. When contacting water, their exchange increases sharply, oxygen absorption more than doubles, ATP content more than triples; sperm are activated and begin to move vigorously at speeds observed in mammalian sperm (164–330 µm/s). Having met the eggs, they penetrate them through the micropyle, after which fertilization occurs. However, sperm do not last long in water. Their energy resources run out, the initial forward movement slows down, becomes oscillatory, then stops and they die. The duration of sperm motility varies depending on the salinity of the spawning environment and temperature; in salt water it is much longer: up to several days for the Pacific herring Clupea harengus pallasi, in fresh water for most fish - carp, salmon, perch - no more than 1-3 minutes.

Table 6

Characteristics of sperm of different fish species

(according to Kazakov, 1978, with abbreviations)

Reproduction is one of the most interesting phenomena that exist on planet Earth. Asexual reproduction appeared about three billion years ago, and sexual reproduction - more than one billion. Methods of procreation have changed over time and acquired different shapes. Both on land and in the ocean, there are many species of organisms that have their own way of reproducing offspring. For example, fish mate in several ways and also reproduce through parthenogenesis and histogenesis.

Fish mate in several ways.

Peculiarities of offspring reproduction

The aquatic environment, which occupies 71% of the planet's surface, has provided organisms with large spaces for existence, from shallow waters to deep bottom waters. Evolution and environmental conditions have created many species of fish with different behaviors and ways of reproducing their young.

To understand the process of fish mating, you first need to understand the structure of the reproductive system. According to statistics, about 80% of all existing species are dioecious. The male reproductive system looks like paired testes with excretory ducts which end in the genital opening. In the female, the efferent ducts connect to the paired ovaries.

There are species of fish called hermaphrodites, in which the male is able to turn into a sexually mature female and vice versa. Gender change can happen once in a lifetime. For example, during its life, a red pagellus can turn from a young female with ovaries into a mature male with testes.

Sexual reproduction

Sexual reproduction of offspring varies in different species. Briefly about the reproduction of fish, we can say that during fertilization, the sex gametes of the male and female merge, after which the formation of a zygote and the further development of the fish occur. Due to the fragmentation of the zygote, an embryo is formed. The fish leaves the egg as a larva. At first, the fish live off the yolk sac. The latter gradually resolves, providing nutrition and growth.

When the yolk disappears, the fish enters the fry stage and feeds on single-celled organisms and small crustaceans (daphnia, for example). The fry grows, switches to other food, and is only distinguished from adult fish by its size.

Fertilization can be external or internal. In most species it occurs in aquatic environment. The female lays eggs, and the male inseminates her with sperm.

Internal fertilization also occurs, for example, in sea ​​bass and guppies. It is carried out with the help of gonopodiums, which are also modified anal fins. Often such reproduction is accompanied by intrauterine development. Bearing offspring has its advantages: protection of fry from predators and the formation in the womb of fry capable of active movement and independent absorption of food.

Parthenogenesis and histogenesis

This is one of the types of reproduction of offspring, while no sperm is involved in the fertilization of the eggs. This method of reproduction is considered sexual, since at least one sexual gamete is involved in reproduction. The egg is capable of developing independently until the crushing stage, and then, interacting with the fertilized eggs, it is activated. Thanks to this, unfertilized eggs do not rot, and the masonry does not deteriorate. Although the egg continues to develop and can reach the larval stage, after it, when the yolk is absorbed, many embryos die.

The exception is the Issyk-Kul chebak. When fish reproduce in this way, they produce numerous viable offspring.

Parthenogenesis occurs in the following families of fish:

• sturgeon;
• salmonids;
• herring;
• and some other types of fish.

Histogenesis, as a type of reproduction of offspring, is a special case of parthenogenetic reproduction. Stimulation of egg activation occurs due to its interaction with the sperm of a male of another species close to the given species. Penetrating into the egg, the sperm stimulates it to further fragmentation, but nuclear fusion does not occur. The egg develops, and from it a full-fledged female organism is formed. Males do not appear during histogenesis.

Histogenesis occurs in silver carps and mollies, whose eggs can be stimulated to develop by the sperm of roach, carp and several other species.

Interesting fact– males do not appear during histogenesis.

Fish instincts

Fertilization is preceded by a series of events. They are a signal of readiness to reproduce.

Stimulation for mating

Many species approach reproduction very responsibly. Salmonids, for example, migrate from salty ocean up freshwater reservoirs for spawning. They can cover thousands of kilometers and carry out dangerous path up fast rivers, exhausting yourself to the end.

In many cases, males (such as guppies) are brightly colored to attract the female. In a mating dance, they circle around the gray females, trying to attract their attention. The lady will choose which male is the most colorful.

Males of other species can build “houses” from silt, mud and other bottom debris. If the female likes the house, the fish mate.

Stimulation for mating of mollies.

Changes to terms and conditions

Fish, like other living organisms, are subject to biological cycles. Mating occurs under certain conditions that occur with the change of season:

• change in daylight hours;
• change in water temperature (to be more precise - its increase);
• increasing the volume of food (fry need to eat a lot, for example, daphnia and single-celled organisms);
• increasing the concentration of oxygen dissolved in water.

The duration of gestation of eggs depends on the type of fish and can range from 12 hours to one and a half months. The age at which fish reach sexual maturity also varies greatly (from several months to 15-30 years). This depends on the species size and habitat conditions. The smaller the fish, the faster it reproduces and the faster it reaches maturity.