Lesson summary "Reproduction and development of fish" | Presentation for a biology lesson (grade 7) on the topic:

How do fish reproduce?

There are monogamous and polygamous, responsible parents and caviar-eating pets.

Sexual method

Sexual reproduction predominates in aquarium fish. Methods for fertilizing eggs:

Interior. Insemination occurs in the body. Characteristic for viviparous women.
Outer. The eggs are fertilized in the pond. Refers to spawn-laying.

Depending on the development of eggs, there are three types:

Viviparous. Development and gestation occurs inside the mother. The embryos feed directly from the mother's body. Breeding is easy due to the high survival rate of the offspring.
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Ovoviviparous. The fertilized eggs are attached to the posterior part of the oviduct. Difference from viviparity - the offspring are separated from the mother's metabolism, nutrition occurs from the contents of the yolk. The mother's body serves only to protect against external threats.
Egg-laying (oviparous). Deposition of eggs in water.

Parthenogenesis

Parthenogenesis means the development of eggs without fertilization by a male. Rarely found in aquarium conditions. From the eggs, male and female individuals emerge, which over time regulates the numerical ratio of the sexes. This type of reproduction occurs in cyprinids, as well as commercial fish. Unfertilized eggs are adjacent to fertilized ones. Viable offspring rarely appear. Parthenogenesis is a sexual method of reproduction, since germ cells are involved, but gamete fusion does not occur.

Gynogenesis

Males and females of different species participate. As with parthenogenesis, the eggs are not fertilized. The male activates the spawning process. Offspring are born only female.

Hermaphroditism

The presence of male and female characteristics, manifested sequentially or simultaneously. Hermaphroditism includes changing sex during life or laying eggs and fertilization by one fish.

Caring parents

No matter how strange it may sound, some fish show reverent care towards their offspring. It is most pronounced in representatives of such families as labyrinthidae, loricariaceae and cichlids.

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South American cichlids form pairs that are able to stay together throughout the life of the fish. During spawning, couples select a substrate suitable for the nest, clean it and spawn eggs, which are closely monitored, periodically fanning them with fins and removing dead eggs. During the breeding season, the character of the fish changes dramatically - they become aggressive and often do not allow other inhabitants of the aquarium to live a quiet life, jealously guarding their clutch and newborn offspring.

Discus fish stand out from the family not only by their appearance and character, but also by their reproductive characteristics. Like other cichlids, they guard the clutch, but when the young emerge from the eggs, they stay close to their parents. During this period, adult fish secrete a special nutritious secretion, which young fish feed on in the first days of life.

African cichlids have an equally interesting way of caring for eggs. Many of them live in harems, where there are several females per male. The spawning itself takes place according to the usual pattern for fish - the female lays eggs on the substrate, and the male fertilizes them. Only then, instead of guarding the nest, the caring mother collects the eggs in a special crop and incubates them for several weeks, after which she releases several dozen completely independent fry.

Another interesting representatives of cichlids are lamprologus fish, whose life cycle takes place next to the empty shells of gastropods. They lay eggs in them and keep their young.

Representatives of labyrinths are characterized by good, responsible fathers. They build nests from foam and plant particles, after which they invite the female to evaluate the home. If the lady is satisfied with the “cradle”, then spawning begins - the male hugs her with his body and squeezes out the eggs, which he then transfers to the nest. After spawning, his attitude towards his girlfriend changes radically: he drives her away and continues to care for the offspring, periodically repairing the nest and picking up fallen eggs and larvae.

Good fathers are also found in loricariid catfish, such as ancistrus. Males of this species occupy oblong caves, clean them, invite females for spawning, and then independently “hatch” the eggs.

Representatives of the ichthyofauna familiar to us can also be surprising. For example, bitterlings inhabiting the Dnieper and Amur basins lay eggs in the mantle of bivalves. As soon as the juveniles hatch, they swim out of their living shelter, carrying the toothless larvae on the surface of their bodies. Pike perch exhibit spawning behavior similar to cichlids - males jealously guard their eggs.

Representatives of marine fish also demonstrate care for their offspring. Male seahorses have a special pouch in which they bear their offspring after spawning.

Video about the development of fish - from eggs to adults:

In most fish, egg fertilization occurs in water. Spermine, entering the water, acquire mobility and, penetrating through the micropyle into the egg, fertilize it. Sperm motility in water lasts for different periods of time in different species. In fish that spawn on the current, where contact between sperm and eggs can be carried out in a very short period of time, sperm moves in the water for a shorter time than in fish that spawn in stagnant water. Thus, in pink salmon and chum salmon, which spawn in fast currents (current speed 0.5-1.0 m sec), sperm motility in water is maintained only for 10-15 sec. In Russian sturgeon and stellate sturgeon, spawning at a slower current (about 0.2 m/sec), sperm motility remains for about 230-290 sec. In the Volga herring - Caspialosa volgensis (Berg) - a minute after placing the sperm in water, only 10% of the sperm remained motile, and after 30 minutes only a few sperm moved. The addition of ovarian fluid to water activates the movement of sperm, which is an adaptation that ensures increased movement when approaching the egg.

In fish species that breed in stagnant water, the possibility of sperm contact with eggs remains much longer than in flowing water, and, accordingly, the viability of sperm is much higher. For example, the sperm of the oceanic herring - C/irea harengus pallasi Val. - retains the ability to fertilize in sea water for more than a day.

In most fish, insemination is external, but in some species, both spawning and those in which eggs develop inside the mother’s body, internal fertilization takes place, and therefore they often develop special copulatory organs. In their simplest form, the organs of copulation are presented in the form of an anal papilla - in lampreys (cyclostomes), as well as in a number of fish - sculpins, gobies and some others.

In male sharks and rays, both viviparous and spawning, internal fertilization occurs. In connection with this, a special copulatory apparatus develops - the pterygopodium (Fig. 80), formed from modified outer inner rays of the ventral fins. These rays increase in size, forming a massive burrow on each pelvic fin, on the inside of which there is a groove. At. During mating, the male puts both outgrowths together and inserts them into the female’s cloaca. Interestingly, the most ancient fossil sharks apparently did not have a copulatory apparatus (pterygopodia), and fertilization was probably external. The modern polar shark, Somtiiosus microcephalus (Bloch.), also lacks pterygopodia, but this is undoubtedly a secondary phenomenon.

Onset of puberty

Development happens:

direct;
indirect.

Direct is characterized by a similar structure of fry and adult fish. Indirect development occurs with transformations: the born individual does not resemble its parents. Those that lay eggs are characterized by an indirect type of development.

To have a similar structure to adult individuals, the offspring go through several stages:

An embryo is formed inside the egg.
After passing through the embryonic stage of development, the future fry enters the larval stage. It begins with a rupture of the egg membrane. The larva has large eyes and an elongated body without fins. In the first few days the larva is motionless.
The whitebait visually resembles a smaller copy of an adult fish. Scales and fins appear.
Gradually the fry grows to adulthood.

Viviparous species produce independent and structurally similar offspring - fry. This is a direct development.

Fish with a short life cycle become ready to reproduce earlier. Already at the age of 2 months, the fish is ready to reproduce. In small cichlids - at 3 months. Large fish with a long lifespan develop by 4-5 years. There are species that mature in 15-30 years. Males reach puberty earlier than females.

Sexual method of reproduction

As a rule, many fish species are unisexual. However, among such individuals there are species called hermaphrodites. Hermaphrodites are individuals capable of developing both eggs and sperm. Although such individuals cannot self-fertilize their eggs, since their reproductive products (eggs or sperm) do not mature at the same time, but in turn. For example, the red pagella is capable of changing sex throughout its life: young pagella individuals are usually females; as the fish matures, the ovaries are replaced by testes.

This ability, hermaphroditism, is also inherent in herring, salmon, carp, and perch species.

Fertilization of eggs also occurs in different ways:

Most fish species reproduce by external fertilization, in which the eggs are fertilized while in water. As a rule, cartilaginous animals reproduce internally, although this type of population increase is also typical for bony (sea bass, eelpout) and carp-toothed (swordtails, guppies, gambusia) species of individuals.

Depending on the development of eggs, all types of fish are conventionally distinguished into the following categories:

viviparous;
ovoviviparous;
oviparous.

The oviparous development method is the most common and involves the deposition of eggs (eggs) directly into the water. In the ovoviviparous method, fertilized eggs are attached to the posterior section of the female's oviduct and continue to develop there until the fry are born. In a word, at the moment of hatching, the eggs break and fry are born.

The ovoviviparous method of reproduction is applicable to most cartilaginous fish species: katran, white shark, fox shark, sawfish and others. Some species, for example, the stingray, have special outgrowths on the walls of the posterior section of the oviduct, which acts as the uterus, thanks to which they can feed their young with nutritious fluid.

The viviparous method involves the formation of a structure in the female's posterior section of the oviduct that resembles a mammalian placenta. It is necessary so that the mother can feed the embryo with nutrients. Viviparity is characteristic of some species of deep-sea sharks.

The main advantage of the ovoviviparous and viviparous methods is the achievement of the greatest survival rate of the young due to intrauterine development.

According to the nature of reproduction, all fish are divided into the following groups:

Monocyclic species are characterized by only one reproduction during their life. With a single spawning, all eggs of an individual may die. River eel, Pacific salmon, river lamprey, Baikal golomyanka and some other fish are called monocyclic due to their single reproduction rate.

Reproduction of viviparous

Livebearers spawn several times a year without creating special conditions. If spawning does not occur, gradually increase the temperature a couple of degrees. Pregnancy proceeds faster at elevated temperatures, but too warm water will result in non-viable offspring.

During the incubation period, the female's abdomen will grow and become noticeably rounder, and when it becomes more square, place the expectant mother for a quiet birth.

Keep the offspring separate from the adults, otherwise the fry will be eaten.

Prepare a separate aquarium or a special trap for breeding aquarium fish. After two weeks, the first sexual signs appear. Sort the fry by sex: individuals with a dark spot on the abdomen are females.

Sexual method of reproduction

Reproduction of spawners

Spawners spawn in different ways. Some species form pairs, others form harems or flocks. The spawning tank is prepared in accordance with the characteristics of the producers.

Dispersal of eggs

Dispersal occurs during school spawning. The eggs scatter randomly and fall onto the ground, leaves and stones. Adult fish do not show parental affection and eat the eggs. To protect the eggs, place the soil in the form of balls with a diameter of 1 cm, cover the bottom with a mesh with small cells.

Masonry formation

The pair form a clutch in a secluded place. The eggs are carefully cared for and protected. Place shelters and broad-leaved plants in the spawning aquarium, where it will be convenient to spawn.

Formation of masonry in caves and gorges

This behavior is typical for fish emerging from aggressive habitat conditions. The spawning ground is equipped with shelters made from piles of rocks, large shells and pots.

Immersion of eggs in the ground

Killie fish, coming from shallow reservoirs with muddy bottoms, form temporary pairs. Pay attention to the soil, choose a substrate based on peat or coconut fibers. Once the parents have spawned the eggs, they can be stored for a couple of months in a warm, dry place. This feature is used when sending eggs by mail.

Nest of bubbles

Labyrinthine fish build nests from air bubbles and pieces of plants. Parents form pairs for life and carefully care for the eggs until the fry appear. When decorating a spawning container, place tall and floating plants. It is imperative to have a tight lid in which an air gap is formed.

Among bony fish there are also a large number of viviparous forms.

In the species-rich order Cyprinodontiformes, a significant proportion of species give birth to live young. In these fish, the modified rays of the anal fin (usually the third and fourth) are transformed into a very complex copulatory organ - the gonopodium. It is interesting that in viviparous carnivores this organ acquires mobility and can turn back and forth.

Rice. 80. Pterygopodium (copulation organ) of the stingray (from Kyle and Eherenbaum, 1927)

A complex gonopodium develops in the fish Horaichthys setnai Kulkarni from Cyprinodontiformes (Fig. 81). Its function is to suspend spermatophores from the female's genital opening. In fish from the order Phallostethiformes, the copulatory apparatus develops on the throat and is a derivative of the first pair of ribs and parts of the pelvic and shoulder girdles. Fish of some other groups also have copulatory organs.

Normal, non-pathological hermaphroditism in fish is very rare.

It is reliably known only among representatives of groupers - Serranidae and sea crucians -

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Rice. 81. Copulatory organs of different fish (not to scale):

L, 2 - male and gonopodium of Gambusia (from Lindbergh, 1934); 3, 4 — male and gonopodium of Horaichthys setnal (from Kulkarni, 1940); 5, 6 — male and Neostethus amaricola (Vill.et Man.)

:Sparidae. In some species of the genus Serranus, self-fertilization is even possible; in other genera Serranidae and Sparidae, the male and female gonads mature alternately, and self-fertilization does not take place.

In some individuals of Chrysophrys aurata (L.), which are hermaphrodites, the milt ripens first and then the eggs, while in others it is the other way around. Therefore, during the spawning period, there are always both “males” and “females” in the herd, although each individual acts differently.

U86 is sometimes either male or female, but self-fertilization does not occur.

The spawning process itself is very different for different fish. In a number of fish, the laying of eggs is preceded by the construction of a special nest. Many catfish of the families Bagridae and Loricariidae lay their eggs in burrows specially dug for this purpose, which are then guarded by males. In this case, something like nesting colonies is formed. Fish such as the common catfish, Silurus glanis L., make nests of plants in various shapes. fish - Amia calva L., some wrasses - Labridae and sticklebacks - Gasterosteidae. A complex floating nest of plants is made by the gymnarchus - Gymnarchus niloticus Cuv. Some labyrinths - Macropodus, Betta, etc. - make nests from air bubbles. The construction of the nest is usually carried out by one male, but in some species, for example, labyrinthine gouramis, the female also takes part in the construction of the nest.

Among fish there are both monogamous and polygamous.

Thus, among salmon, pink salmon usually spawn with one female several males (up to ten), which is apparently associated with spawning in a fast current, when a significant part of the sperm is carried down the river and dies. In the masu salmon, each female usually spawns with one large male. (In masu salmon, dwarf freshwater males often take part in spawning along with large ones); In stickleback, on the contrary, one male spawns with several females, taking turns driving them into a nest that he has built. The wrasse - Creniiabrus ocellatus Forsk. - has two

Rice. 83. Change in the strength of the shell of salmon eggs (according to Zotin):

1 - Sal then salar m. lacustris L.; 2 – Coregonus lawaretus lavaretus awirensls Pravdin

groups of males - large and small. A large male makes a nest of Cladophora, where eggs are laid, inseminated by both large and small males, after which the small males are expelled, and the large one remains at the nest to guard the laid eggs.

Fights over females occur, for example, between male salmon, as well as among some catfish and labyrinth fish. Among salmon and some labyrinths, these fights sometimes end in the death of one of the rivals.

The struggle between males for a female, i.e., so-called sexual selection, is an adaptation that, by weeding out weak individuals, contributes to the preservation of the species.

When sperm penetrates the shell of the egg, as noted above, the droplets in the plasma quickly flow under the shell, which peels off from the yolk, and further penetration of sperm under the shell becomes impossible.

The release of droplets under the egg shell increases its strength (Fig. 83). In the case of unfertilized eggs of sturgeon, salmon, whitefish and other fish that are adapted to reproduce in the current in the water, droplets shoot out under the shell within a few minutes, and the eggs lose the ability to further fertilize. In the herring - Clupea harengus L., the eggs of which develop in sea water that is not very mobile, in most eggs the release of droplets under the shell sometimes occurs later than a day later, due to which such eggs retain the ability to fertilize longer. The liquid contained in these droplets has a negative effect on sperm, causing them to stick together.

In some fish in nature, parthenogenetic development sometimes occurs, which usually differs from normal and, as a rule, does not lead to the formation of a normal larva.

In salmon, unfertilized eggs that are placed in a nest-mound along with fertilized ones do not die, but continue to develop in a unique way.

This parthenogenetic development lasts. for a long time, until the embryos hatch from the fertilized eggs. If unfertilized eggs did not have the ability to develop, but, once in the nest, died and decomposed, this would lead to the death of the entire clutch. The presence of such a peculiar adaptation to parthenogenetic development ensures the preservation of fertilized eggs.

In herring - Clupea harengus membras L. - and in Pacific herring - Clupea harengus pallasi Val. - parthenogenetic development sometimes reaches the stage of a free-swimming larva. Parthenogenesis also occurs in some other species, but there are no known cases of normal development during parthenogenesis in fish. During gynogenesis, that is, when the sperm penetrates the egg, but the fusion of the nuclei of the egg and sperm does not occur, in some species of fish development proceeds normally, but only females are produced in the offspring. This phenomenon was noted in the silver crucian carp - Carassius auratus gibelio (Bloch.) - and in the viviparous fish Molienisia formosa (Girard). Goldfish in East Asia have both males and females in their populations, which ensures normal insemination of eggs. In Central Asia, Western Siberia and Europe, males are extremely rare in populations of silver crucian carp, and in some populations they are even completely absent. In such populations, insemination leading to gynogenesis occurs at the expense of males of other fish species. The adaptive significance of this phenomenon apparently lies in ensuring the reproduction of the population even with the preservation of one female, i.e., under extremely unfavorable conditions.

Caring for offspring is expressed in many fish belonging to different orders.

As mentioned above, many fish make nests from plants, pebbles, and even air bubbles. Many labyrinths lay their eggs in a foam nest built on the surface of the water; In this nest the eggs are guarded by the male. Interestingly, the air bubbles from which the nest is built are enveloped in a film that is stronger than water, secreted by the fish from the mouth. Thanks to this film, the bubbles do not burst.

A very complex nest is made by sticklebacks (Gasterosteus and Pungitius). In these fish, the male builds a spherical hollow nest from scraps of plants, where the females lay their eggs, after which the male remains at the nest and guards it.

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Peculiarities of reproduction of popular fish

Fish reproduction is accompanied by interesting features:

Some fish care for their offspring during the egg stage. Then their parental instincts fade away.
Male cichlids, on the contrary, are overly worried about the offspring and show aggression towards females if they don’t like something in the treatment of the offspring.
A sharp change in conditions in viviparous fish leads to a change in sex from female to male.
Discus fish, angelfish and fairy cichlids take a long time to choose a partner for mating and form a pair for life.

Caring for offspring

The spawning of eggs in large quantities is due to the fact that fish do not tend to care about their offspring . The eggs left behind die from enemies, drying out, and unfavorable conditions; only a relatively small part can survive to the stage of a mature individual.

Some fish that care for their young choose spawning sites in crevices, build nests for protection, or carry eggs in their mouths. Thus, a female salmon uses her caudal fin to clear a place for laying eggs, making a depression on the sandy bottom, then covers the eggs with sand (protecting them from predators and freezing).

Parents provide constant access of oxygen to their offspring and use their fins to aerate the water. To prevent the eggs from drying out, the male waters them with water from his mouth. Manifestations of care in fish are at the instinctive level, when the larvae are able to obtain food on their own, can swim well, and their parents leave them.

Problems

Breed aquarium fish responsibly. Create conditions for future fish in advance. Calculate how much aquarium volume you will need. Often, due to incorrect calculations or too many offspring, fish suffer from overpopulation. When there is not enough space, the fish become aggressive towards each other and experience stress. In an overcrowded tank, the fish grow smaller in size, which leads to subsequent health problems.
Another problem is that the fry do not survive to the teenage stage. The death of fry is caused by improper selection of food and poor water quality. Remember that there should be no large particles of food in the container with the fry.
Avoid inbreeding. Population degeneration occurs due to heterosexual offspring not separated in time. The fish look less bright and may have problems with further self-reproduction. The same applies to closely related species (swordtails, mollies, platies).
If the necessary conditions are created, and the fish do not reproduce or lay infertile eggs, choose another male as the breeder. Most likely, his gonopodium is damaged or he is already old. The lack of offspring is also associated with unsuitable water parameters. If a white coating appears on the eggs, check whether the temperature is suitable for the fish and whether the water is too hard or soft.

Viviparous fish species

Most fish reproduce like this: the female lays eggs, the male releases milk, the eggs fertilized by him undergo a certain incubation period (in the water column, attached to stones, plants or in the oral cavity of the parents), its duration depends on the type of fish, on the water temperature and other conditions external environment, including the quality of food.

The incubation period can be measured in hours, days and even months. At the end of the incubation period, faded or translucent larvae with a huge belly hatch from the eggs (this is the so-called yolk sac, containing reserves of nutrients sufficient to support the life of the larvae in their first days before they gain strength to independently obtain food), transforming after its reduction to normal size, the appearance of scales and rays in the fins into fry, then, as they grow, into juveniles, then into adults. After this, everything is repeated all over again, unless, of course, the fish of this species die after spawning. But there are fish in which the eggs are fertilized not in water, but in the body of the female, where with the help of a special organ (called gonopodium in some fish species, andropodium in others, and pterygopodia in sharks and rays), formed from fused in the form of a tube ventral fins, the male injects seminal fluid, and the development of eggs (incubation) occurs not in water, but in the mother’s body. At the end of the incubation period, the female spawns not eggs, but fully formed fry into the water. In some species, eggs are also hatched, but they have already passed the incubation period, and after entering the water, the fry larvae immediately hatch from them. The first species are called viviparous, the second - ovoviviparous. More than half of the approximately 900 species of sharks and rays found in nature are viviparous or ovoviviparous (according to November 2003, there were 368 species of sharks and 540 species of rays in the world). But these are cartilaginous fish. Of the bony marine fishes, viviparity is observed in Eelpoutidae, Brotuliidae, Sea Perch (from the family Scorpionidae) and Embiotidae. Of the bony fish that live in fresh waters, viviparous fish include a little more than two hundred species - from the Adrianichtidae family (The Adrianichtidae family includes 1-2 species that live in the reservoirs of the island of Sulawesi (Celebes). The length of the fish is up to 20 cm. They serve as objects of local fishing , but are not aquarium and therefore are not considered here. I will only note that they are ovoviviparous: the eggs are fertilized in the body of females, which during spawning spawn eggs. When the latter enter the water, their shells immediately burst, releasing the developed fry), Gudiaceae, Jeninsiaceae , Four-eyed, Poeciliaceae, or Gambusiaceae, and partly from the Half-snouted family. The number of embryos, from which fully viable fry are subsequently obtained, in various viviparous species can be from one to two to three hundred, which is significantly lower than the fertility of egg-laying species from among those that do not care for their offspring and in which most of the eggs and The larvae die during development. Therefore, viviparity, apparently, can be considered as an adaptation in the struggle for the survival of a species in nature. In general, the number of viviparous fish species is small: of all, more than 20 thousand species (according to the latest information, there are more than 28 thousand species of fish in the world) existing in nature, they make up less than 3%, and if we exclude sharks and rays, then even less than 1%. However, there are few among aquarists who would not breed or at least not keep viviparous fish in aquariums. This especially applies to the family Poeciliaceae, or Gambusiaceae, which is not only numerous, but also has the most brightly colored representatives, including those specially bred by humans through hybridization and selection. It makes sense to start talking about viviparous fish with this family.

conclusions

Breed fish by learning the intricacies of spawning the desired species. Get down to business if you have free time and sufficient passion. Choose healthy and vibrant individuals as breeders. Remember that not all species breed in domestic waters. Neons, large catfish, discus and some cichlids are difficult to breed.

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