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. Poor fish, going up the river, often spends everything 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 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 emerge. 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 in rare cases these eggs develop, but only until 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 accommodate 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 is 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 species, no more than 30 days pass between spawnings.

Some oviparous mothers care for their young. And therefore, almost 2 times more days pass between their spawnings. 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.

In this article I will talk about how fish reproduce. In particular, I will consider its types: parthenogenesis, gynogenesis, hermaphroditism, sexual reproduction. I will list the stages of readiness for reproduction, tell you about the rules for setting up a spawning aquarium, and the reproduction process. I will describe what measures need to be taken to successfully raise fry.

There are several ways to breed fish:

1. Bisexual reproduction
2. Parthenogenesis
3. Gynogenesis
4. Hermaphroditism

Most fish species are characterized by sexual reproduction, but there are also methods that occur without fertilization by a male - gynogenesis and parthenogenesis.

Parthenogenesis is a type of reproduction in which the development of eggs occurs without fertilization of the male. However, this method is still considered sexual, since development is carried out from gametes, albeit without the fusion of male and female germ cells. Most often, eggs die at the crushing stage, but they can survive to the larval stage. At the same time, it does not interfere with the fertilized eggs and does not destroy the embryos.

Gynogenesis is one of the types of parthenogenesis. With this form of reproduction, the sperm penetrates the egg and ensures further development, but the fusion of the nuclei of the germ cells does not occur.

In the underwater world, hermaphroditism is often found - the presence of male and female reproductive organs at the same time. In this case, the fish can develop both eggs and sperm. However, self-fertilization is excluded, since the maturation of gametes occurs in different time. And some species of fish (such as wrasses and clownfish) can change sex during life.

In scientific terminology, they are called sequential hermaphrodites. This skill allows females to take the place of the male in the event of his death, and therefore increase the population.

Finally, the most common method of reproduction among fish is sexual, requiring the presence of both a male and a female. It, in turn, is divided into two types:

1. Interior. Fertilization occurs inside the fish's body.
2. Outer. Insemination of eggs occurs in water.

Readiness of fish to reproduce

Different fish go through the stages of readiness to reproduce in different ways. This depends on both environmental conditions and the animal’s lifestyle. But stages are distinguished for all types:

1. Formation of the gonad and germ cell primordia
2. Growth and reproduction germ cells until full maturity
3. Sweeping and fertilization of germ cells

If the first stage occurs in all individuals without exception, even in an unfavorable environment, then the subsequent stages require certain conditions. It is necessary to increase the nutrition of fish two weeks before spawning, provide oxygenated water in the aquarium, and also increase its temperature by 2-3 degrees to stimulate the maturation of gametes.

Once the fish are ready to breed, carry out a number of procedures to prepare for spawning. First, you need to place the female and the male in separate tanks, move them to each other several times for a short time to “get to know each other.” Only then should you build a spawning aquarium.

What should an aquarium spawning tank be like?

The main task of a spawning aquarium is to bring conditions as close as possible to natural environment a habitat.

The breeding process should not be carried out in community aquarium. Adults eat the juveniles, therefore the offspring will be lost.

The spawning tank must provide all the necessary conditions for the successful reproduction of fish. First of all, oxygenated water is required for comfortable spawning. For these purposes, use special plants (for example, agrophila), which also purify the water from contaminants.

High-quality water filtration, lighting and temperature conditions are also important. It is not recommended to fill the bottom big amount soil to simplify the process of cleaning from dirt and feed residues.

The fry are incredibly vulnerable in the first stages of life, so it is necessary to thoroughly disinfect the spawning area. This procedure will save you from life-threatening pathogenic bacteria.

Fertilization process

In most cases, insemination occurs outside the fish's body. Females spawn eggs into the water, and males spawn seminal fluid. The sperm reaches the center of the egg through the micropyle (hole in the shell), the germ cells mix and fertilization occurs.

With the help of pores, the eggs are fed with water and become stronger, and the process of embryonic development begins. Its duration varies from several days to three months until the larva hatches. During the first two or three days, it is saturated with nutrients from the yolk sac and only then is it transformed into a full-fledged fry.

How fry are raised

To begin with, take care of the spaciousness of the aquarium for the fry - full growth and development is impossible in cramped conditions. Then the most crucial period begins - feeding. As the first food, use algal bloom, various organic deposits of underwater plants, rotifers or microworms.

After 3-5 days, feeding can be continued with specialized store-bought formulas. The frequency of feedings after birth should reach 6-7 times a day, and decreases as the young animals develop. Also, do not forget about night lighting - this is important for the primary growth of fry. For final rearing, sort the offspring into 3 groups. Further care is much easier, but regular salt baths are required to prevent fry.

Now you know how fish do fertilization. Before you begin such a labor-intensive process as breeding and growing fish, prepare the necessary conditions for caring for underwater inhabitants. Be sure to equip the correct spawning tank, prepare food and aquarium plants, and provide sufficient lighting. Only after completing these procedures can you expect a successful birth and development of your offspring.

Fish breeding methods

Reproduction methods. Fish reproduce sexually. In rare cases, fish have:

1. Parthenogenesis (development of eggs without fertilization), the development of eggs reaches only the crushing stage (herring, sturgeon, salmon cyprinids) and only in exceptional cases to the larvae that survive until the yolk sac is reabsorbed (burbot, herring). In most cases, such development does not lead to the production of viable juveniles, but in the Issyk-Kul chebak, normal offspring are observed during the parthenogenetic development of eggs. In salmon, unfertilized eggs, finding themselves in the spawning mound in a place with fertilized ones, often develop parthenogenetically. As a result, they do not rot and the entire clutch of eggs does not die.

2. Gynogenesis (birth of females), sperm of related fish species penetrate the egg and stimulate its development, but fertilization does not occur. As a result of such reproduction, only females are observed in the offspring. IN Central Asia, Western Siberia and Europe, there are populations of silver crucian carp, in the reservoirs of Mexico - mollies (order Cyprinodontiformes), consisting almost entirely of females.

Fish are usually unisexual, but there are also hermaphrodites among them. Among bony fish Hermaphrodites include the rock perch, in which eggs and sperm develop in the gonads, but their maturation usually occurs alternately, and the red pagella, in which a change (reversion) of sex occurs during life: in young individuals, the gonads function as ovaries, in older individuals - like testes. Occasionally, hermaphroditism occurs in herring, salmon, carp, and perch fish.

In fish, fertilization occurs:

1) external (in most fish);

2) internal (at cartilaginous fish, in some bony fish - sea bass, eelpout; many carp-toothed animals - gambusia, guppies, swordtails, etc.).

In fish there are:

1) oviparous, laying eggs in the external environment (most species);

2) ovoviviparous, giving birth to fry. Fertilized eggs are retained in the posterior sections of the oviducts and develop there until the young are hatched (most cartilaginous fish - katran, white shark, fox shark, sawfish); in some species, for example, in the stingray, the walls of the posterior sections of the oviducts (“uterus”) even have special outgrowths along which, through the squirters, oral cavity embryos receive nutrient fluid;

3) viviparous - in fish, in the posterior sections of the oviducts (“uterus”), something similar to the placenta of mammals is formed, and the embryo receives nutrients from the mother’s blood ( blue shark, marten shark, etc.).

The adaptive significance of viviparity and ovoviviparity in fish lies in the fact that during intrauterine development, greater survival of the juveniles is ensured.

Depending on the nature of reproduction, fish are divided into:

1) monocyclic - fish die after a single spawn ( river eel, Pacific salmon, river lamprey, Baikal golomyanka);

2) polycyclic - fish reproduce several times during their lives (most fish).

The age of puberty in fish varies significantly - from 1 - 2 months (gambusia) to 15 - 30 years (sturgeon). Fish with short hair mature earlier life cycle(sprat, smelt and some gobies - at the age of 1 year), fish with a long life cycle become sexually mature much later (Atlantic cod - at 7-10 years, sea bass - at 12-15 years, etc.).

The age of sexual maturation of fish depends on the species, the living conditions of the fish, primarily on the feeding conditions. The onset of sexual maturity in fish occurs when they reach a certain length. As a rule, the better a fish is fed, the faster it grows, and therefore the faster it matures. Males usually mature earlier than females.

The rate of ripening is also influenced by climatic conditions. Thus, bream reaches sexual maturity in the Aral Sea at 3-4 years, in the Northern Caspian Sea at 3-6 years, in the Middle Volga at 6-7 years, in Lake Ladoga at 8-9 years.

The age of onset of puberty is important to determine the size of the fish catch and assess raw materials. For short-cycle fish that mature in the 2-3rd year of life (sprat, sprats, sardines, etc.), the permissible commercial removal from the population can be 40-60%, for long-lived fish this withdrawal should be significantly less (5-20%).

Sexual dimorphism. In most fish, sexual dimorphism (secondary sexual characteristics) is not manifested; females and males are externally difficult to distinguish. In some species, secondary sexual characteristics are clearly expressed: females are larger than males, males are characterized by brighter colors, elongated fins, etc.

How fish reproduce: features and methods

Males of polar flounder have ctenoid scales, females have cycloid scales. Males of cartilaginous fish have copulatory organs (pterygopodia), while females do not; in male tench, unlike females, the first ray of the pelvic fins is thickened, etc.

In some fish, during the pre-spawning period, under the influence of sex hormones, a nuptial plumage appears, which disappears after spawning. Many carp and whitefish fish develop horny formations on the head and body of males. white- “pearl rash”; male round gobies become completely black by the time of spawning; The abdomen of the male stickleback turns from silvery to bright red. In Pacific and Atlantic salmon, during spawning, the silver color darkens, black and crimson spots appear on the body, significant morphological changes are observed (the jaws lengthen and bend, changes in the cranial skeleton are observed, pink salmon grow a hump).

Sex ratio. The sex ratio is an adaptive property of fish and is aimed at ensuring successful reproduction. For most fish it is close to 1:1.

The sex ratio of fish can change under the influence of various factors. In guppies, significant development of saprolegnia is sometimes accompanied by the transformation of most of the surviving females into males. Exposure of green swordtail fry to high temperatures results in male predominance.

Hormonal drugs can also help change normal sex ratios in fish. In fish farming, when breeding commercial fish, targeted sex changes can occur by introducing steroid hormones into the feed (rainbow trout).

Among the fish there are:

1) monogamous - usually one male (salmon) spawns with one female;

2) polygamous - there are 3-4 or more males per female (carp) or one male ensures the fertilization of eggs of several females (stickleback).

Timing of reproduction and spawning characteristics. Depending on the timing of reproduction, fish are distinguished:

1) spring spawning (pike, perch, grayling);

2) summer spawning (carp, sturgeon, anchovy);

3) autumn-winter spawning (salmon, Pacific salmon, whitefish, burbot, navaga).

The timing of reproduction of each species, as well as the timing of hatching of larvae and development of juveniles, is related to the availability of their food. Thus, pike reproduces immediately after the ice melts - much earlier than carp fish, which allows its juveniles to reach a length of 5-6 cm and completely switch to feeding on carp fish larvae.

The timing of reproduction of the same species may be different. Thus, capelin near Finnmarken and western Murman spawn from March to May, near eastern Murman - in June-July, in the eastern part Barents Sea- in August-September. Inhabitants of middle latitudes usually spawn once a year, but some of them lay eggs not annually, but at intervals of 2 to 6 years (sturgeon); many tropical fish reproduce several times during the year.

Based on the duration of the spawning period, there are 2 groups of fish:

1) with one-time spawning - all eggs mature at the same time (pike, whitefish, salmon);

2) with portioned spawning - the eggs ripen and are spawned in portions over a long period of time (anchovy, bleak, Caspian herring, catfish, etc.).

In stickleback, the spawning process is measured in a few seconds, in roach and perch - in hours, in carp and bream - in days. Cod, which spawn 3-4 portions of eggs during the spawning season, spends 1.5-2 months on the spawning ground, cod - 3 months.

Often, one and the same species exhibits simultaneous spawning in one body of water and portioned spawning in another. Thus, bream in the Aral Sea exhibit batch spawning; in northern reservoirs (Lake Onega, etc.) it spawns eggs at once.

Portioned spawning is an adaptation of the species to the influence of environmental factors and contributes to increased fertility, greater survival of eggs and larvae, and better nutrition of the young due to the uniform use of the food supply.

Scale, coefficient and maturity index. To assess the degree of maturity of reproductive products in fish, maturity scales are used, of which the most common for polycyclic fish with one-time spawning is a six-point scale.

Stage I - juvenile (juvenales), immature fish. The germ cells of the ovaries are indistinguishable with the naked eye, and the gender is not visually determined. The ovaries and testes look like thin transparent cords of yellowish or pinkish color.

Stage II - maturing individuals or individuals with developing reproductive products after spawning. The eggs are very small and are visible only under a magnifying glass. The ovaries are transparent and colorless, with a large blood vessel running along them. The testes increase in size, lose transparency and look like rounded strands of grayish or pale pink color.

Stage III - individuals whose gonads are far from mature, but relatively well developed. The ovaries fill from 1/3 to V of the entire abdominal cavity, filled with opaque eggs, clearly visible to the naked eye. The testes are dense and elastic. When pressed, liquid milk cannot be extracted from the testes. Their color ranges from pinkish-gray to yellowish-white.

Stage IV - individuals in which the gonads have almost reached full development. The ovaries and testes are the largest in size and fill up to 2/3 of the entire abdominal cavity. The eggs are round, transparent and flow out when pressed. The testes are soft, white, filled with liquid milk, and flow out when pressed.

Stage V - current individuals. The caviar and milt are so mature that they flow freely with light pressure on the abdomen.

Stage VI - spawned individuals (selection). The reproductive products are completely swept out. Gonads in the form of collapsing sacs. Remaining eggs may be observed in the ovaries, and sperm residues may be observed in the testes. The ovaries and testes are inflamed and dark red in color. Some time after reproduction, the ovaries and testes enter stage II of maturity.

In fish with portioned spawning, the stage of maturity is determined by the state of the portion that is most developed and will be spawned first. After spawning the first portion, the ovaries do not move into stage VI, as in fish with simultaneous spawning, but into stage IV or III, and these stages of maturity are designated VI-IV or VI-III. Then, after the completion of the entire spawning period, the state of the ovary is assessed as being in stage VI, and then in stage II. If the remaining oocytes (reserve for the next year) begin to grow already at stage VI, then the ovary from stage VI passes into stage III and is designated VI-III.

When assessing the degree of maturity of fish gonads, the maturity coefficient and index are used.

Maturity coefficient is the ratio of the mass of the gonads to the body mass of the fish (in %). In fish with spring-summer spawning, the maturity coefficient is highest in the spring, decreases in the summer, and begins to increase again in the fall (carp, pike perch, roach, etc.). Fish with autumn-winter spawning have the highest maturity coefficient in autumn (salmon). Maturity index is the percentage ratio of the gonad maturity coefficient, calculated in individual periods of gonad maturation, to the maximum maturity coefficient.

The structure of reproductive products. Fish eggs differ in shape, size, color, the presence of fat drops, and the structure of the shell. In fish, eggs are usually spherical in shape, but other shapes are also found. Representatives of garfish have spherical eggs with thread-like outgrowths; in gobies, pear-shaped eggs at the lower end are equipped with a rosette of threads for attachment to the substrate; in anchovies - ellipsoidal eggs, etc.

The size of the eggs, like other morphological characteristics, is a stable characteristic of the species. Large fish lay eggs of larger diameter. The size of the eggs depends on the nutrient content (yolk) in them and varies significantly. Among bony fishes, the smallest eggs are found in flounder, the largest - in salmon (chum salmon). Cartilaginous fish have the largest eggs, so in heterotoothed sharks 1.5 m long, the length of the egg capsule is about 10 cm. The development of embryos in some of them lasts a very long time - 18-22 months (katran).

The color of the eggs is specific to each species. Eggs that develop in less favorable oxygen conditions are usually more intensely colored. The caviar of vendace is yellow, that of salmon is orange, that of pike is dark gray, that of carp is greenish, and that of greenlings is emerald green, blue, pink and purple. The yellowish and reddish color of caviar is due to the presence of respiratory pigments (carotenoids). Pelagic eggs, which develop with sufficient oxygen, are poorly pigmented.

The eggs of many fish contain one or more fat droplets, which provide buoyancy to the eggs.

The eggs are covered on the outside with shells:

1. The primary - vitelline (radiate) membrane, formed by the egg itself, is penetrated by numerous pores through which nutrients enter the egg during its development in the ovary. In some species this shell is two-layered (sturgeon).

2. Secondary - gelatinous, sticky (develops above the primary shell), with various outgrowths for attaching eggs to the substrate.

At the animal pole of both membranes there is a special channel - the micropyle, through which the sperm penetrates into the egg during fertilization. Teleosts have one canal; sturgeons may have several.

3. Tertiary - horny (in cartilaginous fishes and hagfishes) and protein (only in cartilaginous fishes).

In lampreys, like bony fish, the eggs are small; in hagfish, they are elliptical in shape, 2-3 cm long. The hagfish's cornea has hook-shaped processes, with the help of which the eggs are attached to each other and to underwater objects. The cornea of ​​cartilaginous fish is much larger than the egg itself; often horny filaments extend from it, with the help of which the egg is attached to aquatic plants.

Sperm differ significantly among different fish species. The sperm has a head, middle part and tail. The shape of the head is different: spherical (in most bony fishes), rod-shaped (in sturgeons and some teleosts), spear-shaped (in lungfishes), cylindrical (in sharks, lobe fins). 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 it. The sperm secreted by the male consists of sperm immersed in sperm fluid, similar in composition to saline. In sperm fluid, sperm are immobile. When they come into contact with water, their activity increases sharply. Having met the eggs, they penetrate into them through the micropyle, after which fertilization occurs. The duration of sperm activity depends on the salinity and temperature of the water. In salt water it is much longer - up to several days (Pacific herring), in fresh water- no more than 1-3 minutes (for most fish - carp, salmon, perch).

In one and the same male, sperm are not qualitatively the same and differ in size; upon centrifugation, they are distinguished: small (light), medium (intermediate) and large (heavy). Among large spermatozoa, X-gametes are found in large numbers, and among small spermatozoa, Y-gametes are found. Thus, from eggs fertilized by large spermatozoa, predominantly females are born, and from small spermatozoa, males are born. This is important when artificially breeding valuable fish species.

Laying eggs. The beginning of fish spawning depends on various factors (readiness of reproductive products, temperature and salinity of water, presence of spawning substrate, etc.). From abiotic factors The temperature of the water is important. Each species is characterized by optimal and extreme water temperatures during the breeding season. At negative temperatures, cod, saffron cod, Arctic and Antarctic fish breed. The minimum water temperature at which spawning is possible is -2.3°C for navaga, +3.6°C for cod, +4.5°C for Atlantic herring, and 13°C for carp. For many carp fish, the most intense spawning is observed at temperatures of +18-20° C and above.

Fish lay eggs in different conditions, some species spawn in the tidal zone (lumpfish), others in the oceanic pelagic zone at depths of more than 1000 m (eel). The vast majority of marine fish spawn in relatively warm areas of the coastal zone at depths less than 500 m, where high concentration food organisms and larvae are provided with food. If there are no conditions for reproduction and spawning does not occur or the eggs are not completely spawned, they are absorbed.

Caviar is distinguished:

- pelagic (floating);

- bottom (demersal), deposited on the ground and bottom vegetation.

Depending on the place of spawning, fish are divided into the following groups:

1) lithophiles - lay eggs on rocky and pebble soil (sturgeon, salmon, kutum, shemaya, chub, podust);

2) phytophiles - lay eggs on plants and algae (roach, bream, carp, crucian carp, perch, Pacific herring);

3) psammophiles - lay eggs on the sand (minnow);

4) pelagophiles - lay floating eggs in the water column (sprat, anchovy, Atlantic cod, sabrefish, grass carp, silver carp);

5) ostracophiles - lay eggs in shells bivalves(bitterweeds).

Caring for offspring. Most fish do not care about their offspring. However, there are a number of species that build various nests and protect eggs and larvae.

Pacific and Atlantic salmon use their tails to dig out nests up to 2-3 m long and 1.5-2 m wide in the ground, lay eggs in them, fertilize them and cover them with gravel. The male stickleback builds a nest from plant debris in the form of a muff and guards the eggs. The male pike perch clears a place at the bottom for the future laying of eggs, then guards it, cleans it of silt, washing it away with strong movements of the pectoral fins. If the clutch is left without a guard male, then another one continues guarding. Labyrinth fish build a nest of air bubbles, enveloping them with sticky secretions from the mouth. The male lumpfish guards the clutch of eggs laid in the littoral zone and, when dry, pours water on the eggs from his mouth.

Some fish carry fertilized eggs, for example, the female tilapia holds them in her mouth. The most perfect form of caring for offspring can be considered viviparity in fish.

Fertility and reproductive ability of fish. In fish, there are absolute (individual), relative and working fecundity.

Absolute (individual) fertility is the number of eggs laid by a female during one spawning period.

The fertility of fish is an adaptive property of the species and varies significantly. Cartilaginous fish have the lowest fertility. A manta ray gives birth to one calf. In sharks, fertility ranges from 2 to 100 eggs or fry, and only the Arctic shark lays about 500 large eggs 8 cm long (without cornea). Among bony fishes, the highest fertility is achieved by fish that lay pelagic eggs (sunfish - up to 300 million eggs, moth - about 60 million, cod - up to 10 million eggs).

Fish that care about their offspring are characterized by lower fertility. Thus, the viviparous eelpout lays from 10 to 400 larvae, the stickleback lays 60-550 eggs.

The quantity and quality of caviar depend on body weight, age, fat content and environmental factors. As the fish grows and its body weight increases, absolute fecundity increases.

Fish are able to regulate fertility depending on changing environmental conditions. Greater fertility is produced in species under conditions of more intense mortality. Changes in absolute fecundity are regulated through changes in food supply. Improved feeding conditions lead to faster growth rates and, consequently, higher fertility of similar-sized fish. In this regard, the fertility of one species in different reservoirs is different, reflects the conditions of existence of fish and is aimed at ensuring a certain amount of replenishment.

Relative fecundity is the number of eggs per 1 g of female body weight.

Working fertility is the number of eggs obtained from one female for fish farming purposes. In peled it accounts for about 70% of absolute (individual) fertility.

In some cases, species absolute and population fecundity is calculated.

On the reproductive ability of fish strong influence influences their age, since the quality of reproductive products varies throughout life. In most species, the highest quality offspring come from middle-aged fish. Young and very old individuals produce less resilient offspring.

Duration of the incubation period, survival of eggs and larvae. In fish, the duration of the incubation period ranges from several hours (zebrafish) to 22 months ( spiny shark). Incubation of eggs requires a certain amount of heat, expressed in degree days. This value changes depending on the water temperature. When the water temperature increases (within the limits characteristic of this species), the development of eggs proceeds faster. In carp fish, caviar develops within 3-6 days, in navaga - 3-4 months, in salmon - up to 5-6 months

The population size largely depends on the survival of embryos and the food supply of larvae at the stage of transition to active feeding. These periods account for the highest mortality compared to all other periods of fish life. The main factors determining the survival of embryos and prelarvae are water temperature, salinity, gas regime, wind, and disturbances. The high fertility of some fish cannot indicate their high abundance, since the survival rate of eggs and larvae is very low.

Metamorphosis. In some fish, the development of larvae occurs with metamorphosis (flounder, river eel, sunfish, etc.). Flounder has symmetrical larvae that swim in the upper layers of water with their backs up; over time, they gradually descend into deeper layers of water and lose bilateral symmetry, one eye moves to the other side of the body, and after metamorphosis is completed, the young flounder begins to lead a bottom-dwelling lifestyle . River eel larvae (leptocephali), hatching from eggs in the Sargasso Sea, have a leaf-like shape. Over the course of 2-3 years, they drift with the Gulf Stream, transform into transparent eel-like fish, which enter the rivers of Europe, where they grow, lose transparency and turn into adult eels.

§33. Features of fish reproduction - (answers)

Task 1. Fill in the gaps in the text.

Fish are dioecious animals. They have gonads. In males they are called testes, in females they are called ovaries. Egg cells mature in the ovaries, and spermatozoa mature in the testes. The period of reproduction in fish is called spawning. Fertilization in most fish is external. After fertilization, the fry and fry develop in the ovaries. Substances necessary for the nutrition of fry are contained in caviar. Fish that lay small amounts of eggs have developed care for their offspring.

Task 2. Fill out the table.

Task 3. Write down the numbers of the correct statements.

Statements:

1. Fish are dioecious animals.

2. Gonads of fish - unpaired testes and ovaries.

3. Among fish there are viviparous species.

4. The fertility of fish is associated with high mortality of eggs.

5. Fertilization in fish is always internal.

6. Male and female fish do not differ in appearance from each other.

7. Sharks and rays are ovoviviparous fish.

8. All fish spawn in the spring.

9. The fish larvae emerging from the eggs initially feed on the smallest organisms.

Correct statements: 1, 2, 3, 4, 7.

Task 4. Explain why different species of fish have different timing of the onset of sexual maturity, different fecundity and duration of embryo development.

The time for the onset of sexual maturity varies greatly among different fish species. It is subject to significant changes and varies among different populations of the same species, as well as within the same population. Consequently, the slower a fish grows, the later it reaches puberty and vice versa.

Thus, the time of puberty is associated with food availability, i.e., the abundance of food, and the duration of the feeding period. The smaller the fish, the earlier it becomes sexually mature.

The rate of embryo development is affected by water temperature: at high temperature they develop faster, and at low temperatures they develop more slowly. In this regard, there is a direct relationship between the weather, the progress of spawning and the rate of development of fish embryos.

Task 5. Cod spawns a huge number of eggs - up to 9.3 million pieces. The fertility of three-spined stickleback is very low compared to other fish - from 65 to 550 eggs. Make a guess as to what explains this difference in fish fertility.

The fact is that male sticklebacks selflessly protect their offspring.

How are fish fertilized?

Predators avoid the male standing guard near the eggs. The survival rate of stickleback offspring is many times greater than that of cod. Cod does not protect its offspring in any way. After external fertilization, she abandons her eggs to the mercy of fate. Of course, there are always plenty of animals who are not averse to profiting from such food. Therefore, cod need to lay millions of eggs so that some small part of them survives, passing through numerous feasts arranged by a variety of predators and other animals.

Reproduction and development of fish

Fish reproductive organs

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 into rivers, while others, on the contrary, leave rivers into 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.

Rules and features of the fish reproduction process

A multicellular embryo is formed, in which a yolk sac is visible on the ventral side - the remainder of the nutrient supply of the eggs. In perch, 9-14 days after fertilization, the larva leaves the egg shell and soon begins to independently feed, first on microorganisms, and then 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 their eggs in a pouch on their belly.

From this article you will learn How do Pisces reproduce?. The most detailed instructions and answers to your questions await you on the website botvet.ru

The methods of fish reproduction are varied. Most fish spawn in water, where external fertilization occurs. During breeding, females release large numbers of eggs (spawn) into the cloaca and then into the water, and one or more males of the same species secrete “milt,” a white liquid containing large numbers of sperm.

3 types of fish breeding in an aquarium

There are also fish with internal fertilization, which occurs with the help of pelvic or anal fins modified in such a way that a specialized organ similar to the penis is formed. There are a small number of fish species that are ovoviviparous, that is, the development of fertilized eggs occurs in the cloaca, and not the eggs, but the fry are released into the external environment. Most fish species have paired gonads, either ovaries or testes. However, there are some species that are hermaphroditic, such as the coral reef-dwelling Pomacentra.

Education and studies

For fish reproduction big influence affects the temperature of the water.

For different types of fish, there is a certain range of temperatures most favorable for spawning. If the temperature changes, the fish either do not spawn at all, or spawn without success. But even after successful spawning, there remains a danger of death of the juveniles if the water temperature changes.

Fish bred in ponds spawn only once a year - in spring or early summer, salmon - in winter.

How do aquarium fish reproduce?

The process of fertilization of eggs occurs outside the fish's body. Males and females spawn eggs and sperm into the water. When the germ cells mix with each other, insemination occurs. Of course, the process must end in short term, since sperm and eggs outside the fish’s body in water live for a limited time.

The sperm penetrates the egg through a single hole formed on the surface of the egg - the micropyle. After insemination, the eggs absorb a certain amount of water through their pores, swell and become stronger. After fertilization of eggs begins embryonic development- development of young fish. For different types of fish it lasts for different times: for carp - only a few days, for spring-spawning pike and pike perch - two weeks, for winter-spawning - 2-3 months, until the larva hatches from the eggs. In the first days, each larva feeds on the contents of the yolk sac with which it is born.

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In which insects, in order to fertilize a female, a male must pierce her with his genitals? - Bed bugs mate by traumatic insemination. This means that the female, in principle, does not have a genital opening, and the male has to pierce her abdomen with his genital organ, injecting sperm there.

Is natural parthenogenesis possible in humans?

Parthenogenesis is sexual reproduction involving only maternal cells, that is, the development of an embryo from an unfertilized egg. In addition to the simplest organisms, such as daphnia and nematodes, parthenogenesis has also been observed in more complex animals, such as komodo dragons and certain species of sharks. In mammals wildlife parthenogenesis is impossible due to the so-called genomic imprinting. Only in laboratory conditions, with the help of genetic engineering, was it possible to grow a mouse from an unfertilized egg (one successful outcome out of about 500 attempts). Such operations with human cells make sense only for obtaining stem cells for medical purposes.

Which frogs were able to bear offspring in their stomachs?

The frog Rheobatrachus silus, which lived in Australia and was considered extinct since the 1980s, had a unique method of bearing its young. After laying eggs and fertilizing them by the male, the female swallows the eggs into her stomach. The substance surrounding them, prostaglandin, interferes with the production of gastric juice, so during pregnancy the stomach does not perform its main function. When the time comes, the frog simply spits out the tadpoles.

Which animals did nature poorly “design” for reproduction?

Giant pandas are considered an endangered species and have low level fertility. Chinese scientists from the Panda Research Center in Chengdu came to the conclusion that poor fertility is due, among other things, to the fact that nature poorly “designed” the animals. Females giant pandas They are ready to reproduce only once a year for 72 hours, and only from 12 to 24 hours during this period can they be successfully fertilized. Males, on the other hand, have disproportionately small genitals, which is why sexual intercourse is possible only in a strictly defined position, and males do not know this position well.

In which hermaphrodite animals does the mating ritual take place in the form of fencing with the genitals?

In some species of flatworms, such as Pseudobiceros hancockanus, the mating ritual takes place in the form of fencing with dagger-shaped genitals. Being hermaphrodites, both participants in the fight strive to pierce the opponent’s skin and inject sperm there, thus becoming the father.

How and how successfully are rabbits controlled in Australia?

In 1859, an Australian farmer brought rabbits from England to create a small population and hunt them. Absence natural enemies And ideal conditions to live and reproduce all year round has caused the uncontrolled growth of the rabbit population, which has led to the extinction of many species of native plants. They tried to fight the rabbits by shooting, blowing up holes, poisons, and building mesh barriers, but everything was useless. Finally, in the mid-20th century, the myxomatosis virus spread among them, reducing the population from 600 million to 100 million. However, the surviving individuals acquired genetic resistance to the virus and began to actively reproduce again.

Why do bowerbirds build bowers that serve no useful function?

To attract the attention of females, male bowerbirds build elegant arbors from twigs, decorating them with flowers, shells, berries, butterfly wings and other beautiful objects. These gazebos do not perform any useful function. At the same time, bowerbirds do not hesitate to destroy the buildings of other males or steal decorations from them for their bower. Therefore, by the number of decorations, the female can determine the strength of the male and the ability to protect his property.

Where does the most famous bachelor in the world live?

At one of the research stations Galapagos Islands There lives a male turtle named Lonely George, who is called the most famous bachelor in the world. It is considered the last representative of the Abingdon subspecies elephant turtles. For several decades now, attempts to mate George with females have failed. Although scientists do not despair and continue to search for a suitable match for George, who can live for more than 100 years.

What is the oldest profession that Adelie penguins are not shy about practicing?

Adélie penguins build nests for laying eggs from pebbles. When neighboring couples are distracted, these penguins have no qualms about stealing their rocks. And some females engage in prostitution for the sake of stones, although they have a regular partner. They find lonely males who also make nests in the hope of starting a family, allow them to mate with them, and then take one or more stones to their nest.

What natural disaster is favorable for the reproduction of Melanophila acuminate beetles?

The Melanophila acuminate beetle needs a forest fire to reproduce. When it finds burnt wood, it lays eggs there. The advantage of this method is that at this moment his natural enemies cannot interfere with him, since they themselves are fleeing from the fire. And to detect a fire at a distance of several kilometers, this beetle has a miniature infrared receptor.

In which fish do males bear offspring instead of females?

Offspring seahorses It is the male who carries the baby, not the female. There is a special pocket on the male’s body where the female throws her eggs. This brood chamber is abundantly supplied with blood and plays the role of the uterus.

Whose cubs can devour their potential brothers and sisters while still in the womb?

Different species of sharks give birth to babies in different ways. There are oviparous and viviparous sharks, as well as an intermediate option - ovoviviparous. In them, the development of eggs and the hatching of young from them occurs inside the lower expanded part of the oviduct, usually called the uterus. Some shark larvae may remain in the uterus after hatching and feed on unfertilized eggs.

Where were experiments on crossing chimpanzees and humans conducted?

In the late 1920s, Professor Ilya Ivanov conducted experiments on crossing chimpanzees and humans, but did not achieve results for or against this hypothesis. The experiments were to continue at the Sukhumi Zoo, and even female volunteers were found for insemination with monkey sperm. However, due to Ivanov's arrest in 1930 and his subsequent death in 1932, the experiments were interrupted.

What male animals can pretend to be females?

Some male Australian giant cuttlefish pretend to be females in order to approach and mate with the real female cuttlefish, guarded by a large, dominant male.

Why do ostriches sometimes selectively incubate eggs?

Ostrich eggs most Males incubate for days, and from many females from the flock at once. However, the main female is responsible for the distribution of eggs - she places her own in the center, and the eggs of other females at the edges. Once in Kenya, an ostrich clutch was found consisting of 78 eggs, of which only 21 were hatched. Such wastefulness has a deep biological meaning: numerous predators first of all pick up the eggs scattered around the nest, without touching those that lie in its center.

Which female fish can turn into males?

Cleaner fish live in families of 6-8 individuals - a male and a “harem” of females. When the male dies, the strongest female begins to change and gradually turns into a male.

• Read more: Fish reproduction: procreation

Features of fish reproduction.

The main method of reproduction of fish is sexual. The vast majority of fish species reproduce sexually. At the same time, parthenogenesis and gynogenesis occur in fish, although rarely.

Parthenogenesis is a method of reproduction when the development of eggs occurs without fertilization by males. At the same time, the development of eggs usually reaches only the crushing stage, as for example in herring, sturgeon, salmon and carp. It has been noticed that unfertilized salmon eggs, once in the spawning mound along with fertilized eggs, often develop parthenogenetically. Thanks to this, they do not immediately rot, which is why the entire clutch of eggs does not die, and fry hatch from the fertilized eggs. In burbot and herring, the development of eggs can, in exceptional cases, reach the larval stage, but the latter survive only until the yolk sac is reabsorbed. Thus, in most cases, parthenogenetic development does not lead to the production of viable juvenile fish. The exception is the Issyk-Kul chebak, which produces normal offspring with parthenogenetic development of eggs.

Gynogenesis is the birth of only females from eggs unfertilized by males of a given species. At the same time, the development of eggs is stimulated by sperm from males of related fish species, which are able to penetrate the eggs, but their actual fertilization does not occur. As a result of the gynogenesis path of reproduction, only females are observed in the offspring. Thus, in the reservoirs of Central Asia, Western Siberia and Europe, populations of silver crucian carp are often found in which there are practically no males. Here, the development of crucian carp eggs is stimulated by spermatozoa of carp, roach and some other related species. In the reservoirs of Mexico, there are populations of mollies belonging to the order Cyprinodontiformes, also consisting almost entirely of females.

Most fish species are usually unisexual, although true hermaphrodites are also found among them. The hermaphrodite species among bony fishes includes the rock perch, in which both eggs and sperm develop in the reproductive gonads. However, the maturation of reproductive products usually occurs alternately, due to which self-fertilization of eggs does not occur. In the red pagella, sex reversal occurs during life, i.e. gender reversal. If in young individuals of red pagella the gonads function as ovaries, then in older individuals they function as testes. In addition, hermaphroditism occasionally occurs in some representatives of herring, salmon, carp, and perch fish.

As for the methods of fertilization of eggs in fish, there is external and internal fertilization of eggs. External fertilization occurs in most fish species and occurs in the external aquatic environment. Internal fertilization is more common in cartilaginous fish, although it is also typical for some bony fish, in particular sea bass and eelpout; many carp-toothed fish (gambusia, guppies, swordtails, etc.).

Based on the location of egg development in fish, the following three groups can be conventionally distinguished: oviparous, ovoviviparous and viviparous. Most fish species are oviparous - they lay eggs (eggs) directly into the external aquatic environment. In fish from the ovoviviparous group, fertilized eggs are retained in the posterior sections of the oviducts and develop there until the young are hatched. Those. Almost at the moment the eggs are born, they rupture and immediately the fry are born. Most cartilaginous fish, such as the katran, white shark, fox shark, sawfish and others, are ovoviviparous. In species such as the stingray, the walls of the posterior sections of the oviducts, which act as a “uterus,” even have special outgrowths through which nutrient fluid enters the oral cavity of the embryos through special squirters.

In viviparous fish, a structure is formed in the posterior sections of the oviducts (“uterus”), somewhat similar to the placenta of mammals, thanks to which the embryo receives nutrients along with the mother’s blood. Viviparity is typical for many species of sharks, especially deep-sea ones, and in particular for blue, mustelids, cats and other sharks.

The adaptive significance of viviparity and ovoviviparity in fish lies in the fact that during intrauterine development, greater survival of the juveniles is ensured.

Depending on the nature (multiplicity) of fish reproduction, they are divided into monocyclic and polycyclic. Monocyclic fish reproduce only once in their lives and after a single spawn they all die. Monocyclic fish include river eel, Pacific salmon, river lamprey, Baikal golomyanka and some others. Most fish species are polycyclic, i.e. They reproduce many times during their lives, and the number of reproduction cycles depends mainly on their life expectancy.

The age of puberty in different fish species can vary widely - from 1 - 2 months in small species, such as mosquito fish, and up to 15 - 30 years in sturgeon. Typically, fish with a short life cycle mature faster: at the age of about 1 year, sprat, smelt and some gobies mature. Fish with a long life cycle become sexually mature much later. Thus, Atlantic cod matures at 7–10 years, sea bass at 12–15 years, etc.

At the same time, the age of sexual maturation of fish depends not only on the species, but also on the living conditions of the fish, and primarily on the feeding conditions. Therefore, the onset of sexual maturity in fish usually occurs when they reach a certain length. It follows that the better a fish is fed, the faster it grows, and therefore the faster it matures. Males in most fish species usually mature earlier than females.

Climatic conditions also have an important influence on the rate of ripening. For example, in the Aral Sea, bream reaches sexual maturity at the age of 3–4 years, in the Northern Caspian Sea at 3–6 years, while in the Middle Volga at 6–7 years, and in Lake Ladoga only at 8–9 years.

To determine the size of fish withdrawal (catch) from a particular reservoir and assess raw material resources, the age of puberty is important. Therefore, for short-lived fish that mature in the 2nd–3rd year of life, the permissible commercial removal from the population can be 40–60% (sprat, sprats, sardines, etc.), while for long-lived fish the annual removal should not exceed 5–20%.

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 the individual development of fish, a number of large segments can be distinguished - periods, each of which is characterized by properties common to different species.

I. Embryonic period– from the moment of fertilization of the egg until the juveniles switch to external nutrition. The embryo is nourished by the yolk, a food supply 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) subperiod of the free embryo (prelarva), when development is underway 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. Energetic resources The build-up is mainly consumed. 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 capable of reproducing its own kind; secondary sexual characteristics, if they are characteristic of a given species, are present. Energy is spent primarily on the development of the reproductive system and the creation of reserves to maintain life activity during migrations , wintering, breeding.

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 of 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. A stage denotes any given point in development.

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

Fish are characterized by 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 only reaches the crushing stage, and only in exceptional cases were viable larvae obtained that lived until the yolk sac was completely reabsorbed (herring, Sakhalin herring, burbot, chebak, perch).

Some species of fish (goldfish Carassius auratusgibelio, molinisia Molinisia formosa) are characterized by a completely unusual method of 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, penetration of the sperm into the egg is a necessary condition for 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 of 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 ways specific features caused by an aquatic lifestyle.

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 great death 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. The number of eggs laid by different species 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. In the same individual, fertility - all other things being equal - first increases with growth, then decreases with old age, despite 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 a 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 – in the 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, in Far Eastern salmon, eels, and 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, the pectoral fins of males are larger than those of 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 are 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 of bivalves, are very peculiar: 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 spawns in different areas at different times: 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 once: roach and perch spawn in a short period of time (one morning). Many tropical fish spawn within an hour. All eggs of such fish intended for hatching in a given season ripen immediately and are completely swept out.

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

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

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 living conditions. 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 marine pelagic eggs the water content reaches 85–97%, due to which they are lighter than sea water, while in bottom eggs it is up to 60–76%), an increase in the perivitelline space due to the presence of fat droplets in the yolk ( many herrings, flounders) 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 a 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 the 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 nutrition of the embryo - the yolk of the oocyte - consists mainly of proteins, the bulk of which are represented by lipophosphoproteins (ichthulin) and a small amount of albumin, and lipids (mainly phosphatides, primarily lecithin, as well as 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 content of proteins in them varies greatly (from 12–14 to 29–30% of wet weight) and fats (from 1–2 to 22% of 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 between 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 a small amount of 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,

gch – 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 their biological properties, in particular in the nature of the gametes: among large spermatozoa there are large numbers of X-gametes, among small sperm there are 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: the size, age and condition of the males, spawning conditions - currents, temperature, the 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)