What is hermaphroditism
If a fish simultaneously or sequentially has male and female sexual characteristics, as well as reproductive organs, then this is hermaphroditism. In other words, such fish can develop both eggs and sperm. However, they are not able to self-fertilize eggs, since the maturation of the reproductive products does not occur simultaneously, but alternately. Some fish can change sex several times in their life. The ability to hermaphroditism is in such fish as guppies, sea wrasse, red pagellas, herring, carp, salmon, perch.
A few words about productivity
Productivity refers to the number of offspring a fish can produce. In aquarium individuals, it can be from several tens to several thousand. The number of eggs directly depends on age, heredity, health, nutrition and living conditions. Less fertile fish are “good parents”, that is, those that take care of the offspring, for example, incubate it in the mouth, carry it on the body, etc.
What is parthenogenesis
Parthenogenesis in fish is a method of sexual reproduction when the female’s eggs do not need fertilization by a male.
This method is considered sexual, since the development of the body comes from the reproductive cell, albeit without the fusion of male and female gametes. In fish, it is quite rare and just as rarely leads to the “hatching” of viable juveniles.
Unfertilized caviar, which develops in this way, perfectly coexists with fertilized eggs, does not rot and does not destroy the clutch. It can develop to the larval stage, but when the yolk sacs are absorbed, the larvae usually die. However, most often, caviar develops only up to the stage of crushing.
Parthenogenesis can be found in fish such as herring, sturgeon, carp, salmon.
This type of breeding is most common among fish. He needs a female and a male. At the same time, eggs can be fertilized in different ways:
- In an internal way. Insemination takes place inside the body of the fish. Found in swordtails, guppies, mosquitoes and other viviparous species.
- Externally. Fertilization of eggs takes place in water. Found in most fish species.
The development of eggs is also uneven. And depending on it, fish are:
- Viviparous. In the posterior part of the female oviduct, there is a structure similar to the mammalian placenta. Thanks to her, the mother can provide the embryos with the necessary substances. Caviar develops in 30 to 50 days. Near the anal fin during this period, a dark “pregnancy spot” can be observed. If the breeder noticed that the female’s abdomen became rectangular, then after three days fry can be expected. They are born on their own, floating and able to feed. Viviparous are guppies, swordtails, mollies, formosa, etc.
- Ovoviviparous. Fertilized eggs attach to the oviduct, or rather its posterior part, and develop there until fry appear. This is the case with most cartilaginous fish. sharks and rays.
- Oviparous. They lay eggs directly into the water. This method is the most common.
Scientists also distinguish fish that reproduce monocyclic, that is, once in a lifetime (river eel, river lamprey, Pacific salmon, and others) and polycyclic, that is, several times throughout life (this is the majority of fish).
There is also a classification depending on which substrate is spawning:
- Lithophiles with masonry on rocky ground;
- Psammophiles with masonry in the sand;
- Phytophils with clutch on plants;
- Ostracophiles with clutch in the mantle cavity of the mollusk;
- Pelagophiles with eggs floating in the water column;
- Pelophiles with clutch in silt.
Some fish species are indifferent to the substrate, while others build special nests from plants, air bubbles, etc.
Discus feeding the fry with a nutritious secret.
How to determine if a fish is ready to breed
Everything is individual here. Some species, for example mosquito fish, are ready to give offspring already 1-2 months after their birth. Others will take 15-30 years to reach puberty. The ripening time is influenced by:
- Life cycle: the shorter it is, the earlier it ripens, and vice versa;
- Species affiliation;
- Habitat and climate.
If the fish has a “mating outfit”, then it is ready to give offspring. This can be a bright color, age spots, overgrowth of the skin, etc.
It is possible to determine the female representatives of the cyprinidae and haracin family ready for spawning by looking at their abdomen. when it is filled with caviar, it becomes round and full, even if the fish is hungry.
And here are a couple more interesting facts:
- Males reach puberty earlier than females.
- In young fish, the first few spawns are unproductive.
Male cockerel caring for the nest.
What is gynogenesis
Gynogenesis is considered a special case of parthenogenesis. It takes place without the participation of males of this species. Stimulation of eggs to development is accomplished by the spermatozoa of males of other fish species close to this one. The sperm enters the egg, but the fusion of their nuclei does not occur. There are absolutely no males among the “newborn” fry. Gynogenesis occurs in mollies and goldfish. The eggs of the latter stimulate the development of spermatozoa of carp, roach and some other species.
How fish breed
Reproduction is an interesting phenomenon of the life cycle of organisms, which ensures not only their existence, but also evolution. The life of fish surprises with its diversity and adaptability to a wide variety of conditions. Reproduction can occur at different ages and in different ways. Some fish spawn with or without fertilization, others give birth to small fish, and some even lay eggs in molluscs. Let’s find out more about fish breeding.
As strange as it may sound, some fish show reverent care in relation to their offspring. It is most pronounced in representatives of such families as labyrinth, loricaria and cichl.
Cichlids of South America form pairs that are able to survive throughout the life of the fish. During spawning, couples choose a substrate suitable for the nest, clean it and spawn eggs, which they watch vigilantly, 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 give a quiet life to other inhabitants of the aquarium, jealously guarding their clutch and newborn offspring.
Discus stand out from the family not only for their appearance and character, but also for their breeding characteristics. Like other cichlids, they guard the clutch, but when the young emerge from the eggs, they keep closer to their parents. During this period, adult fish secrete a special nutritional secret, which young fish feed on in the first days of life.
African cichlids are also distinguished by an equally entertaining way of caring for caviar. Many of them live in harems, where there are several females for one male. Spawning itself takes place according to the usual scheme for fish. the female spawns eggs on the substrate, and the male fertilizes it. Only then, instead of guarding the nest, a caring mother collects eggs in a special goiter and bears them for several weeks, after which she releases several dozen completely independent fry.
A pair of scalars caring for masonry.
Another amusing representatives of cichlids are lamprologus fish, whose life cycle passes next to the empty shells of gastropods. In them, they lay eggs and contain juveniles.
Representatives of the labyrinth are characterized by good, responsible fathers. They build nests from foam and plant particles, after which they invite the female to evaluate the dwelling. 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 dramatically: he drives her away and continues to look after the offspring himself, periodically repairing the nest and picking up the fallen eggs and larvae.
Good fathers are also found in Loricaria catfish, such as the Ancistrus. Males of this species occupy elongated caves, clean them, invite females for spawning and then independently “incubate” eggs.
Representatives of the familiar fish fauna can also be surprising. For example, bittersweet inhabiting the Dnieper and Amur basins lay eggs in the mantle of bivalve molluscs. As soon as the juveniles hatch, they swim out of their living shelter, carrying away the toothless larvae on the surface of their bodies. Zander exhibits cichlid-like spawning behavior. males jealously guard their clutch.
Representatives of marine fish also show concern for offspring. Male seahorses have a special bag in which they carry offspring after spawning.
Asexual reproduction methods
1) Division of unicellular organisms (amoeba). With schizogony (malaria plasmodium), not two, but many cells are obtained.
2) Spore formation
- Spores of fungi and plants are used for reproduction.
- Spores of bacteria do not serve for reproduction, because K. One bacterium forms one spore. They serve to experience adverse conditions and resettlement (by the wind).
3) Budding: daughter individuals are formed from the outgrowths of the body of the mother’s body (kidneys). in coelenterates (hydra), yeast.
4) Fragmentation: the maternal organism is divided into parts, each part turns into a daughter organism. (Spirogyra, coelenterates, starfish.)
5) Vegetative propagation of plants: propagation by means of vegetative organs:
- Roots. raspberries
- Leaves. violet
- Specialized modified shoots:
- Bulbs (onions)
- Rhizome (wheatgrass)
- Tuber (potato)
- Usami (strawberry)
Sexual and asexual reproduction
|Two organisms involved||One organism involved|
|Sex cells (gametes) obtained by meiosis are involved||Somatic cells that multiply by mitosis are involved.|
|Children are different (there is a recombination of the characteristics of the father and mother, the genetic diversity of the population increases)||Children are the same, copies of the parent (in agriculture. allows you to quickly increase the number of organisms, while maintaining all the characteristics of the variety)|
Sexual reproduction methods
1) With the help of gametes, sperm and eggs. Hermaphrodite is an organism that forms both female and male gametes (most higher plants, coelenterates, flat and some annelids, molluscs).
2) Conjugation in the green alga Spirogyra: two threads of Spirogyra approach each other, copulation bridges are formed, the contents of one thread flows into another, one thread is obtained from zygotes, the second. from empty shells.
3) Conjugation in ciliates: two ciliates approach each other, exchange genital nuclei, then diverge. The number of ciliates remains the same, but recombination occurs.
4) Parthenogenesis: a child develops from an unfertilized egg (in aphids, daphnia, bee drones).
You can also read it. Part 1 assignments
Choose the one that is most correct. Reproduction, in which a daughter organism appears without fertilization from the cells of the body of the mother’s body, is called 1) parthenogenesis 2) sexual 3) asexual 4) seminal
UNLESS Choose three options. Asexual reproduction is characterized by the fact that 1) the offspring has genes only of the maternal organism; 2) the offspring is genetically different from the maternal organism; 3) one individual participates in the formation of offspring; 4) splitting of traits occurs in the offspring; 5) the offspring develops from an unfertilized egg; 6) a new individual develops from somatic cells
SEXUAL EXCEPT 1. All but two of the following terms are used to describe asexual reproduction. Identify two terms that “fall out” from the general list, and write down the numbers under which they are indicated. 1) schizogony 2) parthenogenesis 3) fragmentation 4) budding 5) copulation
All but two of the following terms are used to describe the asexual reproduction of living organisms. Identify two terms that “fall out” from the general list, and write down the numbers under which they are indicated. 1) fragmentation 2) seed reproduction 3) sporulation 4) parthenogenesis 5) budding
All but two of the examples below refer to asexual reproduction of organisms. Identify two examples that “fall out” from the general list, and write down the numbers under which they are indicated. 1) reproduction by spores of ferns 2) reproduction of earthworms by fragmentation 3) conjugation of ciliates-shoes 4) budding of freshwater hydra 5) parthenogenesis of bees
SEXUAL. SEXUAL CHARACTERISTICS 1. Establish a correspondence between the peculiarity of sexual and vegetative reproduction and the method of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the correct order. A) forms new combinations of genes B) forms combinative variability C) forms offspring identical to the maternal D) occurs without gametogenesis E) is due to mitosis
Establish a correspondence between the characteristics and methods of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the order corresponding to the letters. A) Haploid nuclei merge. B) A zygote is formed. C) Occurs through spores or zoospores. D) Combinative variability is manifested. E) The offspring is formed, identical to the original individual. F) The genotype of the parent is preserved over a number of generations.
Establish a correspondence between the stages of the life cycle of plants and methods of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the order corresponding to the letters. A) spores are formed B) accompanied by fusion of gametes C) sporophyte multiplies D) gametophyte multiplies E) zygote is formed E) meiosis occurs
Establish a correspondence between the characteristics and types of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the order corresponding to the letters. A) Reproduction is carried out using shoots. B) There is a combination of genes of the two parents. C) The body develops from an unfertilized egg. D) Reproduction occurs without the participation of gametes. E) Reproduction occurs by budding. E) A zygote is formed.
SEXUAL. SEXUAL EXAMPLES 1. Establish a correspondence between the example of reproduction and its method: 1) sexual, 2) asexual. Write down the numbers 1 and 2 in the correct order. A) sporulation in sphagnum B) seed reproduction of spruce C) parthenogenesis in bees D) reproduction by bulbs in tulips E) laying eggs by birds F) spawning in fish
Establish a correspondence between a specific example and a method of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the correct order. A) sporulation of fern B) formation of Chlamydomonas gametes C) formation of spores in sphagnum D) budding of yeast E) spawning of fish
Establish a correspondence between a specific example and a method of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the correct order. A) hydra budding B) division of the bacterial cell in two C) the formation of spores in fungi D) parthenogenesis of bees E) the formation of strawberry whiskers
Establish a correspondence between the processes and methods of reproduction of organisms: 1) sexual, 2) asexual. Write down the numbers 1 and 2 in the order corresponding to the letters. A) laying eggs by lizards B) sporulation of penicilli C) reproduction of wheatgrass by rhizomes D) parthenogenesis of daphnia E) division of euglena E) reproduction of cherries by seeds
Establish a correspondence between examples and methods of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the correct order. A) raspberry cuttings B) spore formation in horsetail C) spore formation in cuckoo flax D) lichen fragmentation E) aphid parthenogenesis E) budding in a coral polyp
D) division of the common amoeba E) fragmentation of the mycelium in fungi E) root suckers in raspberries
A) tissue culture B) unfertilized eggs C) tubers D) eggs
E) somatic cells E) rhizome areas
A) the formation of spores in the fly agaric
B) reproduction of strawberries by whiskers C) fusion of mammalian gametes
VEGETATIVE EXCEPT 1. All but two plant breeding methods listed below are referred to as vegetative propagation. Identify two techniques that “drop out” from the general list, and write down the numbers under which they are indicated. 1) division of tubers 2) reproduction by rhizome 3) obtaining seedlings from seeds 4) artificial insemination 5) formation of layering
VEGETATIVE. SEXUAL 1. Establish a correspondence between the peculiarity of reproduction and its type: 1) vegetative, 2) sexual. Write down the numbers 1 and 2 in the correct order. A) due to a combination of gametes B) individuals are formed by budding C) provides genetic similarity of individuals D) occurs without meiosis and crossing over E) due to mitosis
SEXUAL 1. Select three traits that are characteristic of the sexual reproduction of seed plants and write down the numbers under which they are indicated. 1) Sperm and eggs are involved in reproduction 2) As a result of fertilization, a zygote is formed 3) In the process of reproduction, the cell is divided in half 4) The offspring retains all the hereditary characteristics of the parent 5) As a result of reproduction, new characters appear in the offspring 6) The vegetative parts of the plant participate in reproduction
Choose three correct answers out of six and write down the numbers under which they are indicated. What are the characteristics of sexual reproduction? 1) genetic diversity of offspring 2) simple cell division 3) budding 4) development of offspring after fertilization 5) parthenogenesis 6) provides growth, cleavage, regeneration
SEXUAL EXCEPT All but two of the terms below are used to describe the sexual reproduction of organisms. Identify two terms that “fall out” from the general list, and write down the numbers under which they are indicated. 1) gonad 2) spore 3) fertilization 4) ovogenesis 5) budding
SEXUAL. SEXUAL DIFFERENCES 1. Select two differences between sexual reproduction and asexual reproduction. 1) sexual reproduction is energetically more favorable than asexual 2) two organisms participate in sexual reproduction, one in asexual 3) during sexual reproduction, descendants are exact copies of the parents 4) somatic cells participate in asexual reproduction 5) sexual reproduction is possible only in water
Choose three correct answers out of six and write down the numbers under which they are indicated. What is the difference between sexual reproduction and asexual reproduction? 1) promotes the appearance of modifications 2) increases the number of offspring 3) enhances the genetic diversity of offspring 4) increases the fertility of individuals 5) forms new combinations of genes 6) leads to a variety of allele combinations in gametes
= Choose three correct answers out of six and write down the numbers under which they are indicated. Bacterial spores, in contrast to fungal spores, 1) serve as an adaptation to endure adverse conditions 2) perform the function of nutrition and respiration 3) DO NOT serve for reproduction 4) ensure proliferation (dispersal) 5) are formed by meiosis 6) are formed from the mother cell by loss of water
Reproduction, development of bony fish and their diversity
Reproduction and development of bony fish
The reproductive organs of bony fish differ from the reproductive organs of cartilaginous ones. The sex glands are paired. The eggs are excreted by the formed oviducts, and the Müllerian canals are reduced. The oviducts grow together with the ovary at one end, and open the genital opening outward with the other. Fertilization is often external, in a few species, internal in a few species. When the sex cells mature, the instinct of reproduction is manifested in fish. At this time, they move to places more favorable for development and offspring. Fish of some species rush from the sea to the rivers, while others, on the contrary, leave the rivers to the sea. These are the so-called migratory fish. They travel long distances to spawn.
Most fish are dioecious. Females spawn eggs, glued in the form of ribbons, onto aquatic plants. Males spew milk at this time. Motile spermatozoa swim up to the eggs and penetrate them. The complex instinctive behavior of fish during the breeding season is called spawning. Fish caviar is small, several millimeters. The fertilized egg begins to divide. A multicellular embryo is formed, in which the yolk sac is visible on the ventral side. Remaining nutrient reserves of eggs.
Representative of bony fish. Sturgeon.
Development in most fish proceeds with metamorphosis. In this case, larvae emerge from the eggs, which differ from the adults in a number of signs. At first, they feed on the yolk preserved in the yolk sac, and later they switch to active feeding in some fish, the larvae have external gills, which later disappear. The body of the larva undergoes a number of changes, in some groups (for example, flounder, eels, herring), very significant. The final acquisition by the larva of an appearance close to the appearance of an adult fish usually occurs from the moment scales appear on its body. from that time the larva becomes a fry. Fry less than a year old are usually called underyearlings. Fish live from a year (some gobies) to 50-70 years (pikes, carps, halibuts); for the most part, life expectancy is not more than 15-20 years. Fish larvae and fry have many enemies: they are devoured by predatory insect larvae, crustaceans, hydroids and jellyfish, arrow worms, frogs, snakes, birds, etc.
Fish reach sexual maturity at the age of several months (tulka) to 6-11 (cod) and 16-20 (beluga) years. Matured fish usually spawn annually, aging fish do not spawn every year, and by the end of their life they stop multiplying. Some species spawn only once in a lifetime, after which they die. These are Far Eastern salmon, some herring, Azov and Caspian gobies. The fecundity of fish ranges from a few dozen eggs (in some arctic slingshots, in gobies) to 1-9 million eggs (in flounders and codfish) and even 28 million (in a fish moon). But from this huge number of eggs, only a few individuals reach the adult state. Eggs are either heavier than water (bottom eggs) and are deposited by fish on the bottom, on aquatic plants, or burrow into the ground, or their specific gravity is approximately equal to the specific gravity of water, and it floats near the surface or in the water column (pelagic eggs). Most fish lay eggs under strictly defined environmental conditions, specific to each species and much less variable than those under which fish usually live outside of breeding time. To lay eggs, fish gather in places with a certain temperature, salinity, aeration, alkalinity, soil or substrate (for fish with bottom eggs); all of these factors can be significant. Developing eggs and larvae, especially at an early stage of development, are usually much more sensitive to environmental factors than adult fish; therefore, spawning under strictly defined values of these factors contributes to their better survival. The desire of fish to gather for spawning in places and conditions most suitable for the development of eggs contributes to the concentration of producers necessary for reproduction, as well as the isolation of different species from each other.
Most fish spawning pelagic eggs limit the care of the offspring by approaching certain spawning grounds, places and environmental conditions favorable for the development of spawned eggs. For example, cod and herring spreading for fattening in the northern waters of the Atlantic Ocean up to Svalbard and Novaya Zemlya are collected for spawning in the warmer coastal waters of Norway. Salmon feeding in the open ocean come to the shores, enter rivers and rise to spawn in their upper reaches with clear, transparent water.
Variety of bony fish
Most species of fish belong to the class of bony fish. over 20,000. There are two classes of bony fish: ray-finned (Actinopterygii) and lobe-finned (Sarcopterygii). Fish are the largest class of vertebrates in terms of the number of species; they number up to 20-25 thousand species, which are combined into 33 orders. Units of the class of bony fishes: amie-like, aravan-like, atherine-like, batracho-like, beryx-like, gonorhynchiformes, puffer-like, flounder-like, carps-toothed, carp-like, cephalic-like, cetacean-like, beak-like, thistle-like, mycose-like, salmon-like, bag-like. percopsiformes, sucker-like, horn-toothed, sargan-like, herring-like, scorpion-like, merged-saber-like, sun-like, cat-like, spin-like, tarpon-like, cod-like, eel-like, angler-like, coelacanth-like.
I will give a description of some orders of bony fish.
Sturgeon detachment. Representatives of the order sturgeon belong to the subclass cartilage. These are the most ancient bony fish in origin, with some features resembling sharks. Their axial skeleton is represented by a chorda, which persists for life. The vertebral bodies are undeveloped, but their cartilaginous arches are laid. But sturgeons have gill covers, a swim bladder, and bony parts of the skeleton. Modern cartilaginous fish. Bottom forms. These include sterlet, sturgeon, stellate sturgeon, beluga, kaluga. In contrast to cartilaginous fish, they have overhead bones of the skull, bony gill covers, bony base of the skull, outside along the body there are three or five rows of large bone plaques and small bony grains between them. Sturgeon feed on animal food, most often. Invertebrates. Food is collected using the rostrum, digging at the bottom. Large sturgeon (beluga and kaluga) can feed on fish, and sometimes young seals. Beluga lives in the waters of the Volga-Caspian basin sometimes up to 100 years and reaches a mass of up to 1,000 kg. Far Eastern kaluga is not inferior to it in size. “Queen of Cupid”.
A typical representative of sturgeon. Russian sturgeon, inhabitant of the Volga-Caspian and Black Sea basins. This is an anadromous fish that lives in the sea, but goes into rivers for spawning. The sturgeon has no teeth, and it gropes for food with its antennae, and then pulls out its mouth (rostrum) and draws it into the pharynx. It feeds on shellfish. For winter, it lies in deep holes, most often in the mouth of the river. In spring it goes against the current to the rivers for spawning. Eggs develop in the bottom layer of water. Juveniles slide down the rivers into the seas, where they live until maturity.
The sterlet, unlike other sturgeons, spends its entire life in fresh water. She is the smallest of them. It feeds on insects. Its weight reaches 3-6 kg.
Sturgeon are of great commercial importance. Meat, caviar (black) and even chord are used for food. But due to overfishing and a number of changes in the environment, the number of sturgeon fish has significantly decreased. Therefore, fishing on them has decreased. Some types. Sterlet, sturgeon, Black Sea beluga. Listed in the Red Book.
Detachment herring. Representatives of the herring order have a flat silvery body, a very short lateral line, or it is completely absent. The head of the herring is not covered with scales, the fins are soft. The swim bladder is constantly connected to the intestines.
Most herrings live in the water column and feed on plankton. About 300 species of these valuable commercial fish are known. The most common are Atlantic and Pacific herring. Their body length is 40-50 cm. The Atlantic herring inhabiting the Baltic Sea is called herring. The Black Sea herring lives in the Black Sea (body length up to 40 cm, weight up to 1 kg). Part of the individuals leaving for spawning in the river. Danube is called Danube herring. The Black Sea sprat, tulka and others are found in the Black Sea. Anchovy fish belong to herring: European anchovy, or anchovy, which are of great commercial value.
Squad salmon. Their body is round or slightly compressed from the sides. Salient feature. Presence of an adipose fin located on the dorsal side in front of the caudal fin.
Most salmonids. Anadromous fish (salmon), but some species constantly live in fresh waters (trout, whitefish, omul, etc.). Many salmonids are widespread in the Far East, for example chum salmon, pink salmon, red salmon, chinook salmon, etc. During spawning, they migrate over a distance of several thousand kilometers (chum salmon, 1,000 km, chinook salmon, 4,000 km). In the reservoirs of the CIS countries there are salmon such as European grayling, trout, Danube and Black Sea salmon. Trout lives in mountain rivers, it is artificially bred in Transcarpathia, Crimea.
Salmon. Commercial fish, highly valued for high quality meat (“red fish”) and red caviar.
Detachment carp. The order of carp has about 3000 species, most of which live in fresh water bodies. Some of them go to spawn in the sea (roach, ram). They have soft fins, a swim bladder like herring. No teeth, but there are pharyngeal teeth that serve to grind food.
Squad of perch. Squad of perch. About 6500 species. A characteristic feature is that their swim bladder loses its connection with the intestines and exists on its own. Fins with spines. The body length is from 1 cm to 5 m, and the weight reaches 500 kg. For example, swordfish. Length 4 m, weight 300 kg. She, chasing prey, can reach speeds of up to 120 km per hour. Perch include tuna (up to 3 m long and 680 kg in weight), horse mackerel, gobies.
In the Black Sea there are: common mackerel, common horse mackerel, common tuna, gobies. In the fresh water bodies of the country, commercial species such as river perch and pike perch are widespread. A number of representatives of perch. Common goby, golden goby, striped ruff. Listed in the Red Book.
Bony fish are of great practical importance for humans. Millions of people are engaged in fishing, breeding and processing fish, building boats and making fishing equipment. In some countries, the population feeds mainly on fish, and its well-being depends mainly on the size of the catch. Hundreds of thousands of people are fond of fishing and spearfishing, and this wonderful sport gives them health and relaxation. There are even more aquarists creating a colorful, quiet world in the glass vessels of their aquariums. In addition to food products, fish are used as raw materials for obtaining medicine (fish oil), feed for livestock and poultry (feed meal), fertilizer for fields (fertilizer), technical fat, glue, leather and other products used in the food and light industry.
Breeding methods for fish
Reproduction methods. Fish reproduce sexually. In rare cases, fish have:
Parthenogenesis (development of eggs without fertilization), the development of eggs only reaches the stage of crushing (herring, sturgeon, salmon cyprinids) and only in exceptional cases to the larva that survive until the yolk sac is absorbed (burbot, herring). In most cases, such development does not lead to the production of viable juveniles, but in the Issyk-Kul gudgeon with parthenogenetic development of eggs, normal offspring are observed. In salmon, unfertilized eggs, finding themselves in a spawning hillock 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.
Gynogenesis (the birth of females), spermatozoa of closely related fish species penetrate into the egg and stimulate its development, however, 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 goldfish, in the water bodies of Mexico. Mollies (order carps-toothed), consisting of almost some females.
Fish are usually unisexual, but there are also hermaphrodites among them. Among teleost fishes, hermaphrodites include rock perch, in which eggs and sperm cells develop in the gonads, but their maturation usually occurs alternately, and red pagella, in which a sex change (reverse) occurs during life: in young individuals, the gonads function as ovaries, in more senior. Like testes. Occasionally, hermaphroditism occurs in herring, salmon, carp, perch fish.
In fish, fertilization is:
1) external (in most fish);
2) internal (in cartilaginous fishes, in some bony fishes. Sea bass, eelpout; many fish-toothed fish. Gambusia, guppies, swordtails, etc.).
Fish are distinguished:
1) oviparous, laying eggs in the external environment (most species);
2) ovoviviparous, giving birth to fry. Fertilized eggs are retained in the posterior parts of the oviducts and develop there until the fry hatch (most cartilaginous fish. Katran, great white shark, fox shark, pilonos); in some species, for example, in the stingray stingray, the walls of the posterior parts of the oviducts (“uterus”) even have special outgrowths, through which nutrient fluid enters the oral cavity of the embryos through the spray;
3) viviparous. In fish, in the posterior parts of the oviducts (“uterus”), something similar to the mammalian placenta is formed, and the embryo receives nutrients from the mother’s blood (blue shark, marten shark, etc.).
The adaptive value of viviparity and ovoviviparity of fish lies in the fact that during intrauterine development, a greater survival rate of juveniles is ensured.
Depending on the nature of reproduction, fish are divided into:
1) monocyclic. Fish die after a single spawning (river eel, Pacific salmon, river lamprey, Baikal golomyanka);
2) polycyclic. Fish reproduce several times during their life (most fish).
The age of onset of sexual maturity in fish varies considerably. From 1.2 months (mosquito fish) to 15.30 years (sturgeon). Fishes with a short life cycle mature earlier (tulka, 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 old, sea bass. At 12-15 years old, etc.).D.).
The age of sexual maturation of fish depends on the species, living conditions of the fish, primarily on the conditions of feeding. The onset of sexual maturity in fish occurs when a certain length is reached. As a rule, the better a fish eats, the faster it grows, and therefore, the faster it ripens. Males usually mature earlier than females.
The ripening rate is also influenced by climatic conditions. So, in bream, sexual maturity occurs in the Aral Sea at 3-4 years, in the Northern Caspian at 3-6, on the Middle Volga at 6-7, in Lake Ladoga at 8-9 years.
The age of puberty is important for determining the size of fish catch and estimating raw material resources. In short-cycle fish that ripen in the 2-3rd year of life (sprat, sprats, sardines, etc.), the allowable commercial withdrawal from the population can be 40-60%, in long-lived fish this withdrawal should be much less (5-20% ).
Sexual dimorphism. In most fish, sexual dimorphism (secondary sexual characteristics) is not manifested, females and males are outwardly difficult to distinguish. In some species, secondary sexual characteristics are pronounced: females are larger than males, males are characterized by brighter coloration, elongated fins, etc. Males of the polar flounder have ctenoid scales, females. Cycloid. 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, in the pre-spawning period, under the influence of sex hormones, a mating outfit appears, which disappears after spawning. In many cyprinids, whitefishes, horny formations of white color develop on the head and body of males. “Pearl rash”; round goby males 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 silvery color darkens, black, crimson spots appear on the body, significant morphological changes are observed (the jaws lengthen and bend, changes in the cranial skeleton are observed, the humpback salmon grows a hump).
Sex ratio. The sex ratio is an adaptive property of fish and is aimed at ensuring successful reproduction. In most fish, it is close to 1: 1.
The sex ratio in 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 fry of green swordtails to high temperatures leads to predominance of males.
Among the fish are distinguished:
1) monogamous. One male usually spawns with one female (salmon);
2) polygamy. There are 3-4 or more males per female (carp) or one male ensures the fertilization of eggs of several females (stickleback).
Breeding terms and features of spawning. Depending on the timing of breeding, 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, are associated with their food supply. So, the 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 larvae.
The breeding time of the same species may be different. For example, capelin near Finnmarken and western Murman spawns from March to May, near eastern Murman. June-July, in the eastern part of the Barents Sea. In August-September. Inhabitants of middle latitudes usually spawn once a year, but some of them do not lay eggs annually, but at intervals from 2 to 6 years (sturgeon), many tropical fish reproduce several times during the year.
According to the duration of the spawning period, 2 groups of fish are distinguished:
1) with one-time spawning. All caviar ripens at the same time (pike, whitefish, salmon);
2) with portioned spawning. The caviar ripens and is washed in portions for a long time (anchovy, bleak, Caspian herring, catfish, etc.).
In stickleback, the spawning process is measured in a few seconds, in roach and perch. For hours, at the carp and bream. Day and night. Cod, spawning 3-4 portions of caviar during the spawning season, spends 1.5-2 months on the spawning ground, the sultan. 3 months.
Often, one and the same species in one body of water is observed a one-time, and in another portioned spawning. Thus, bream in the Aral Sea is observed to spawn in portions, in northern water bodies (Lake Onega, etc.), it spawns at the same time.
Portion spawning is an adaptation of the species to the effects of environmental factors and contributes to an increase in fertility, greater survival of eggs and larvae, and better nutrition of fry due to the uniform use of the food base.
Scale, coefficient and index of maturity. To assess the degree of maturity of reproductive products in fish, maturity scales are used, of which the six-point scale is the most common for polycyclic fish with a single spawning.
Stage I. Juvenile (juvenales), immature fish. The sex cells of the ovaries are indistinguishable with the naked eye, and the sex is not visually determined. The ovaries and testes look like thin transparent bands of yellowish or pinkish color.
Stage II. Ripening 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, along with a large blood vessel. The testes grow in size, lose their transparency and look like rounded bands of grayish or pale pink color.
Stage III. Individuals in which the gonads are far from maturity, but relatively well developed. The ovaries fill from 1/3 to Y of the entire abdominal cavity, filled with opaque eggs, clearly visible to the naked eye. Testes are dense, elastic. When pressed, liquid milk cannot be extracted from the testes. Color them. Pinkish gray to yellowish white.
Stage IV. Individuals in which the sex glands are almost fully developed. The ovaries and testes are the largest 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, flow out when pressed.
Stage V. Current individuals. Caviar and milk are so ripe that they flow freely with light pressure on the abdomen.
Stage VI. Spawned individuals (outflow). Sex products are completely swept away. Gonads in the form of collapsing bags. In the ovaries, the remaining eggs can be observed, in the testes. Remains of sperm. The ovaries and testes are inflamed, dark red. Some time after reproduction, the ovaries and testes pass into the II stage 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 the first portion is left, the ovaries do not go to stage VI, as in fish with a single spawning, but to IV or III, and these stages of maturity are designated VI-IV or VI-III. Then, after the end 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 (the reserve of the next year) begin to grow already at stage VI, then the ovary from stage VI goes into III and is designated VI-III.
When assessing the degree of maturity of fish gonads, the coefficient and maturity index are used.
Maturity coefficient. The ratio of gonad mass to fish body mass (in%). In fish with spring-summer spawning, the maturity coefficient is highest in spring, decreases in summer, and begins to increase again in autumn (carp, pike perch, roach, etc.). Fish with autumn-winter spawning have the highest maturity coefficient in autumn (salmon). Maturity index. Percentage ratio of the gonad maturity coefficient, calculated in separate periods of gonad maturation, to the maximum maturity coefficient.
The structure of the reproductive products. Eggs of fish differ in shape, size, color, presence of fat droplets, structure of the shell. In fish, eggs are usually spherical, but other forms are also found. The representatives of the sargan-like are different. A spherical egg with filamentous outgrowths; in goby. Pear-shaped eggs at the lower end are equipped with a rosette of threads for attachment to the substrate; in anchovy. Elliptical eggs, etc.
The size of the eggs, like other morphological characters, is a stable feature of the species. Large fish lay eggs of larger diameter. The size of the eggs depends on the content of the nutrient (yolk) in them and varies considerably. Among teleost fishes, the smallest eggs are found in the limand flounder, the largest. In salmon (chum salmon). Cartilaginous fish have the largest eggs, for example, the 1.5 m long egg capsule is about 10 cm long in multi-toothed sharks. The development of embryos in some of them lasts a very long time. 18-22 months (katran).
The color of the eggs is specific for each species. Caviar developing under less favorable oxygen conditions is usually more intensely colored. The vendace has yellow caviar, and salmon. Orange, pike. Dark gray, carp. Greenish, among the greens. Emerald green, blue, pink and purple. The yellowish and reddish color of caviar is due to the presence of respiratory pigments (carotenoids). Pelagic eggs developing with sufficient oxygen content are poorly pigmented.
Eggs of many fish contain one or more fatty droplets that provide buoyancy to the eggs.
Eggs are covered with shells outside:
Primary. The yolk (radiant) 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-layer (sturgeon).
Secondary. Gelatinous, sticky (develops above the primary membrane), with various outgrowths for attaching eggs to the substrate.
A special channel is located at the animal pole of both shells. The micropyle, through which, during fertilization, the sperm enters the egg. Teleosts have one canal; sturgeons may have several.
Tertiary. Horny (in cartilaginous fish and myxins) and protein (only in cartilaginous).
In lampreys, as in teleost fishes, the eggs are small; in myxines, they are ellipsoidal, 2-3 cm long. On the cornea, the myxines have 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; corneous filaments often extend from it, with the help of which the egg is attached to aquatic plants.
Sperm cells differ significantly between different fish species. In the sperm, the head, middle part and tail are distinguished. The shape of the head is different: spherical (in most teleost fishes), rod-shaped (in sturgeons and some teleosts), spear-shaped (in dioecious), cylindrical (in sharks, cross-finned). The core is placed in the head. An acrosome is located in front of the nucleus in sharks, sturgeons and some other fish. Bony ones do not have it. The sperm secreted by the male consists of spermatozoa immersed in sperm fluid, similar in composition to saline. In the sperm fluid, the sperm are immobile. When in contact with water, their activity increases sharply. Having met the eggs, they penetrate them through the micropyle, after which fertilization occurs. The duration of sperm activity depends on the salinity and temperature of the water. It takes much longer in salt water. Up to several days (Pacific herring), in fresh water. No more than 1-3 minutes (in most fish. Carp, salmon, perch).
In the same male, the spermatozoa are not qualitatively the same and differ in size; during centrifugation, they separate out: small (light), medium (intermediate) and large (heavy). Among large spermatozoa, X-gametes are found in large numbers, and among small Y-gametes. Thus, from eggs fertilized with large spermatozoa, mainly females are born, small. Males. This is important for the artificial breeding of valuable fish species.
Spawning. The start of fish spawning depends on various factors (readiness of reproductive products, temperature and salinity of water, the presence of a spawning substrate, etc.). Water temperature is an important abiotic factor. During the breeding season, each species is characterized by optimal and extreme water temperatures. Arctic cod, navaga, Arctic and Antarctic fish breed at subzero temperatures. The minimum water temperature at which spawning is possible is 2.3 ° C for cod, 3.6 ° C for cod, 4.5 ° C for Atlantic herring, and 13 ° C for carp. In many cyprinids, the most intensive spawning is observed at temperatures of 18-20 ° C and above.
Fish lay eggs in different conditions, some species spawn in the intertidal zone (pinagor), 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 of less than 500 m, where a high concentration of food organisms and larvae are provided with food. If conditions for breeding are absent and spawning does not occur or eggs are not completely spawned, they are absorbed.
Depending on the place of spawning in fish, the following groups are distinguished:
1) lithophiles. Eggs are laid on stony-pebble soil (sturgeon, salmon, kutum, shemaya, chub, podust);
2) phytophils. They lay eggs on plants and algae (roach, bream, carp, crucian carp, perch, Pacific herring);
3) psammophiles. They lay eggs on the sand (minnow);
4) pelagophiles. Floating eggs are laid in the water column (sprat, anchovy, Atlantic cod, sabrefish, grass carp, silver carp);
5) ostracophiles. They lay eggs in the shells of bivalve molluscs (bittersweet).
Caring for offspring. Most fish do not care for their offspring. However, there are a number of species that build various nests, protect eggs and larvae.
Pacific and Atlantic salmon tail up 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 stickleback male builds a nest from plant residues in the form of a muff and protects the eggs. A male pike perch clears a place at the bottom for future egg laying, then protects it, cleans it of silt, washing it away with strong movements of the pectoral fins. If the clutch remains without a guard male, then the guard continues with another. Labyrinth fish build a nest from air bubbles, enveloping them with sticky secretions from the mouth. The male pinagora protects the eggs laid in the littoral zone and, when dry, sprinkles the eggs from the mouth with water.
Some fish carry fertilized eggs, so the female tilapia keeps it in the mouth. The most perfect form of caring for offspring can be considered live birth in fish.
Fertility and reproductive capacity of fish. In fish, there are absolute (individual), relative and working fertility.
Absolute (individual) fertility. 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 considerably. Cartilaginous fish have the lowest fertility. The manta ray gives birth to one cub. In sharks, fertility ranges from 2 to 100 eggs or fry, and only the polar shark spits about 500 large eggs 8 cm long (without a cornea). In teleost fishes, the greatest fecundity is observed in fish spawning pelagic eggs (moonfish. Up to 300 million eggs, moth. About 60 million, cod. Up to 10 million eggs).
For fish that take care of the offspring, less fertility is characteristic. So, a viviparous eelpout spawns from 10 to 400 larvae, a stickleback lays 60-550 eggs.
The quantity and quality of caviar depends on body weight, age, fat content and environmental factors. With the growth of fish and an increase in its body weight, absolute fertility increases.
Fish are able to regulate fertility depending on changing environmental conditions. High fertility is developed in species under conditions of more intense mortality. The change in absolute fertility is regulated by the change in food supply. Improving feeding conditions leads to an accelerated growth rate, and therefore to a higher fecundity of the same size fish. In this regard, the fertility of one species in different water bodies is different, reflects the conditions for the existence of fish and is aimed at ensuring a certain amount of replenishment.
Relative fertility. This 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 breeding purposes. In peled, it is about 70% of the absolute (individual) fertility.
In some cases, the species absolute and population fecundity is calculated.
The reproductive capacity of fish is strongly influenced by 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 give less viable offspring.
The duration of the incubation period, the survival rate of eggs and larvae. In fish, the incubation period ranges from a few hours (zebrafish) to 22 months (barbed shark). To incubate eggs, a certain amount of heat is required, expressed in degree days. This value changes depending on the water temperature. With an increase in water temperature (within the limits typical 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 size of the population largely depends on the survival of the embryos and the provision of food for the 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 that determine the survival of embryos and prelarvae are water temperature, salinity, gas regime, wind, and waves. 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, larval development proceeds with metamorphosis (flounder, river eel, moonfish, etc.). The flounder has symmetrical larvae that swim in the upper layers of the water with their backs up, over time they gradually sink into deeper layers of water and lose bilateral symmetry, one eye passes to the other side of the body, and after the completion of metamorphosis, the young flounder begins to lead a bottom lifestyle. Eel larvae (leptocephalic) hatching from eggs in the Sargasso Sea are leaf-shaped. Within 2-3 years they drift with the Gulf Stream, turn into transparent eel-like fish, which enter the rivers of Europe, where they grow, lose their transparency and turn into adult eels.