The most interesting phenomenon of the life cycle of the organism, ensuring its existence and evolution, is reproduction.
In 1987, E. K. Balon hypothesized that the main method of reproduction of fossil fishy (500-430 million years ago) was pelagophilia, with plankton caviar and larva. Live birth has arisen in the Silurian; gestation on the body and protection of the offspring appeared in the Carboniferous, egg production and egg breeding finally took shape at the end of the Cretaceous period.
There is nothing surprising in the fact that many aquarists soon have a desire to get offspring from their pets. either because some species have multiplied in the aquarium, or in order to preserve certain fish. Everyone who contains rare or endangered animals should be aware of their responsibility for their protection, especially if the natural population is rapidly declining. Currently, lawmakers are discussing the possibility of banning the catch of rare (possibly all) fish species, which means that the existence of many species in aquariums will depend entirely on their captive breeding. You can also play an important role in this business, and not just multiply them for the sake of interest or pleasure.
Unfortunately, breeding aquarium fish often not carried out according to the plan and (or) for reproduction defective individuals are taken, which leads to the degeneration of the breed. Those species, many generations of which lived and multiplied in aquariums, now represent only a pitiful similarity to their excellent wild ancestors. Many fish are prone to disease due to the lack of natural selection, which weakens the effect of closely related crosses. Comparing modern representatives of the species with pictures of their ancestors just 20-30 years old, aquarists are horrified.
Due to the high adaptability of fish to their habitat breeding aquarium fish took on multiple forms. Gynogenesis. activation, but not fertilization of the egg by the sperm cell. in the offspring of predominantly female (silver carp, petilia formosis, etc.). Hermaphroditism. one individual can be both male and female (rivulus marmoratus, stone grouper, etc.). Guppies have hermaphroditism and even self-fertilization. The transformation of the floor (Betta Fish, Malawian cichlids, live beetles etc.); parasitism (anglers), etc. The copulative organs of males. modified fins, anal papilla and urogenital papilla are used for internal fertilization (pantodon, bullhead, half-fish, soma, gudiyevye, etc.). In Brazilian striped Jeninia (Jenynsia lineata) copulation lasts 5-10 minutes. When oviductatory eating (eaters, golomyanka, gambuziyevye) fry partially develop in the body of the female or hatch from the calf just before the birth. In the four-eye eyes (Anableps), already in the yolk sac of the embryos, filaments and villi appear, which serve to suck up the juices from the walls of the oviducts.
However, the distinctive feature of most fish is the external fertilization and development of caviar. Through a special aperture (micropyle), the sperm cell (only in sharks. polyspermia) quickly penetrates the egg cell. After fusion of germ cells, it closes (when breeding soft-water fish in a highly mineralized environment, the micropyle does not open and fertilization does not occur).
With external fertilization, sperm live from 0.5 to 5 minutes, with internal fertilization. from 2 months to 2 years. Stable water inhabitants have higher semen viability. In industrial fish farming, sperm (without water) is kept full for 2 or more days using special preservatives (1% alcohol) at a temperature slightly above 0 ° C. The phenomenon, when the eggs of one female are fertilized by several males, is called polyandry. In the case of a spawning spawning, water happens to grow turbid from the set of milks released by males (in one drop about 300 million lively beetles). In such a situation, the water after 15-30 minutes is changed to 2/3 with fresh, identical chemistry and temperature.
Productivity aquarium fish varies from tens to several thousand pieces. Age, condition and size of females, hereditary factors, habitat and good nutrition influence the number of developing caviar. Smaller fecundity is characteristic of species that take care of the offspring (viviparous, incubating eggs in the mouth, bearing offspring in brood chambers, on the body, etc.). When artificially incubating caviar of Malawi and Tanganyik cichlids, it is necessary to carefully monitor the purity of the environment, since one timelessly not removed egg can ruin the whole clutch.
Portion spawning (continuing at intervals throughout the year) is typical for tropical fish, seasonal or one-time, for many cold-water fish or species living in stable conditions (cave, deep-water, etc.). In relation to the substrate, the fish are divided into lithophils, which lay eggs on stony ground; psammophils spawning in the sand; phytophils breeding among plants; ostracophiles. caviar is washed into the mantle cavity of mollusks, under the shell of crabs, etc.; pelagofilov. eggs and embryos develop, swimming in the water column; pelophils prefering silt. Often the species are indifferent to the substrate, they scatter eggs with equal success in the midst of plants, on sand, etc. Demersal, non-sticky caviar sinks to the bottom. In a number of fish, nest laying is preceded by the construction of a nest: from the plants of the nine-stick stickleed, lepidosiren, pollymir Isidor, Limnarch, a real gourami, etc.; from air bubbles, "cemented" by saliva, in Hoplosternums, Diane, Kallicht, Kupanus, Lyalius, etc.; in the soil of false tesparii, papiliochromes, cancer, herothilapias, hemichromes; Arnold’s copella places the eggs on the inside of the leaves of the plants hanging above the water, and so that the clutch does not dry out, it sometimes periodically sprinkles it with tail strokes. Pigmentation, the shape and size of the eggs also have an adaptive characteristic aimed at the survival of the population. Optimal manufacturers become only when physiological maturity is combined in them with the maturity of the body (size not less than half the maximum length, strength of the constitution, etc.). Males usually mature earlier than females (the maturation process activates the addition of thyroxin to water). When old males are crossed with young females, males dominate in the offspring, while young males spawn with elderly females, the number of females increases. Large females and small males of the same: age give more males, the opposite combination. females. In general, the first spawning is unproductive. The relative mass of the gonads increases in fish with age. Inhabitants of drying-out water bodies from the family of kartozubyh reach sexual maturity as early as 2-3 months, and the Mudarya lizlopatonosa in 5-6 years (most aquarium fish ripen in 8-18 months and retain this ability for at least another 2 years). Immediately after spawning, almost all Far Eastern salmon, ayuvye, noodle fish, some gobies (pagolovki, caspiosomes, latrunculus) and Baikal slingshots (golomyanka, etc.) perish.
The course of maturation of genital products in fish is assessed on a 6-point scale: 1. immature young; 2. first mature or individuals of previous spawning, sex is distinguishable; 3. the sex glands are relatively well developed, the ovaries occupy from 1/3 to 1/2 the volume of the abdominal cavity, contain small yellowish eggs, testicles are dense, elastic, pink-yellow-white; 4. the ovaries occupy 2/3 of the body cavity, the eggs acquire a color close to the norm, the testes are milky-white (hence the derivative is milt), when pressed, sperm is released; 5. fluid, fertile individuals. spawning; 6. spawned individuals, ovaries and testicles in which flabby. In fish with portion spawning, sex products mature with doses calculated for the entire cycle. The amount of ovovitelin, phospholipids, magnesium, vitamins A and B in the serum at this time increasesone. Readiness for breeding is judged by the appearance of fish in a nuptial dress (bright coloration, pigment spots in cichlids; pearl rash on the head and gill covers in carps; growth of the skin of the uricaric catfish; a change in the shape of the head in Far Eastern salmon, etc.), swelling anus and an increase in ovipositor and spermicon.
Marital attire serves to recognize the sexes, stimulate the ripening and release of sexual products. As a rule, caviar is deposited with fish in the evening or early in the morning. The spawning period varies from 30 minutes to several hours and even days at rest. brachidanio, atherine, princess Burundi, etc. The increase in productivity can be achieved by separate keeping and correct feeding of the producers for 10-15 days before spawning. Key stimuli stimulating breeding aquarium fish, may be individuals of another sex, composition (pH, dH, EH), movement, substitution, water level, temperature changes, duration and intensity of illumination (moon phases in Indian carp fish, catfish), substrate (soil, vegetation, and with a certain configuration leaves and bushiness, etc.), the composition of microorganisms, the presence of satellite fish, water-soluble, species-specific metabolites responsible for breeding aquarium fish (kopulin), etc. So, putting aquariums in direct sunlight stimulates the coloring, growth and breeding of young females. The cyclical spawning also depends on the length of daylight. Adding to the feed calf thymus leads to an increase in the number and size of offspring, feeding fry the thyroid gland accelerates metamorphosis, but slows growth.
Before breeding fish, you should check the availability of feed to future offspring. The best food for juveniles will be "live dust", so all breeding plans for the period from April to September (in the absence of cultured organisms). The monogamy (pair family) includes four teeth: tsikhlovye, nandovye, snakeheads, etc., to polygamy (schooling family). iris, goby, eleotrovye, stickle, etc. School spawning (in carp, harakov, etc.) is not always justified, especially if the fish destroy their eggs. In such cases, the amount of substrate should be increased, and spawning grids should be laid at the bottom. Fishes with high intraspecific aggressiveness (distichodes, leporins, trophies, etc.) should be gradually accustomed to each other or increase the area of spawning grounds and the number of shelters. The volume of breeding aquariums can vary greatly. For nanostom is 200 ml, and for a pair of discus not less than 100 liters. Fish taking care of the offspring (Loricaria catfish, anabasic, cichl, etc.) are capable of raising young animals in the general aquarium. But usually the development of caviar takes place either in adjustable containers or in special incubators, modifications of the Weiss apparatus, etc. Methylene blue, rivanol (1-2 mg / l), malachite green, purple K, oxalate bright green (0.5-2 mg / l) are added to the water for disinfection.
With the development of caviar, as a rule, 6 phases are distinguished:
1. Dead, unfertilized roe without signs of crushing (early removal after spawning).
2. Not yet developed, but fertilized (in opaque caviar, the division goes on the sharp end).
3. Germinal disc.
4. Transparent, young embryo.
5. Pigmented embryo.
6. Pigmented eyes embryo.
Overcrying caviar does not reduce its fertilization ability, but greatly increases the percentage of waste during development. The moment of pigmentation of the eyes of the embryo (eye stage) indicates that the critical periods of development have been left behind. In such a state, eggs can be subjected to transportation and other manipulations without significant harm to the embryo (insignificant death is also observed in the early, immediately after spawning, stages). The formation of eggs and embryos accelerates temperature, the increased content of oxygen, iron in water (up to 1 mg / l), vitamin B2 sometimes an increase in salinity (0.5–3% o). The process of hatching regulates a special enzyme. chorionase. Mass hatching can be stimulated by adding to the calf water from the aquarium, where the fry have just been bred, or freshly thrown caviar shells. The sum of temperatures multiplied by the number of hours or days of incubation is approximately a constant value, referred to as degree-days or degree-hours. For trout at 2 ° C, the development lasts 205 days (410 degree-days), at 5 ° C-82 days (410), at 10 ° C-41 days (410 degree-days). After embryo hatching, the dose of the drug is gradually reduced to zero (water change, filtration with activated charcoal), and the mineralization of water (for softwater fish) is slowly raised. A free embryo has a yolk sac with a supply of energetic substances that feed it in the first hours or days of life. At this time, he leads a passive existence, lies on the ground, is suspended from plants, bark and stones with the help of a cement organ or adhesive threads. In multidimensional organs, the attachment organ arises due to the protrusion of the intestinal wall, in African and American biloba, it is a transverse groove in the pharynx area, in most bony fish it forms on the upper side of the snout or in the brain part of the head. The gill covers and pseudo-larvae in the larvae supply oxygen to the brain and eyes, while the capillary networks of the blood vessels, the yolk bladder, the pectoral, dorsal, anal fins and external gills provide the rest of the body. Bag resorption is a signal to immediately feed the ear to an actively moving larval embryo. Petrochromes, digiotylia, etc. To stimulate the resorption of the bag and the correct differentiation of the gastrointestinal tract, micro doses of plankton are set 3-5 days earlier than expected. The larva becomes malcom only acquiring scaly cover and the structure of adult fish.
A well-grown, equal in size (undead and overgrown culled), healthy juveniles with desirable traits (brightness and purity of color, proportions of the body and fins, mobility, etc.) are selected for the tribe, from which spawning pairs or groups are subsequently formed. This is the so-called mass selection. In purposeful work and keeping diaries, one can take into account internal, equally important features: growth rate, disease resistance, maturation rate, etc. Here individual selection takes effect, consisting in evaluating each particular producer for the quality of offspring or comparing quality indicators several families (family selection). Skillful combination of both selection methods will ensure the best possible results.
Free crossing in nature of all individuals (often at a subspecific level) is called panmixia. Numerous experiments on sexual selection have shown that the female chooses the most brightly colored male during copulation. Thus, the golden principle in the final set of pairs will be the best for the better.
Without knowledge of the fundamentals of genetics today it is impossible to competently deal with the reproduction of any animals, and in particular fish. Selection of fish is based mainly on the selection of quantitative characteristics, due to changes in both internal (genotype) and external (phenotype) factors. Hereditary deposits (genes) of germ cells (gametes) are closely related to the behavior of fibrous, helically twisted structures. chromosomes, enclosed in the nuclei of cells. Genes are segments of a continuous DNA molecular chain (deoxyribonucleic acid). The commands transmitted by chromosomal DNA using transport RNA to numerous ribosome protein synthesizers scattered throughout the cell are based on the genetic code that determines the order and ratio of amino acids (their number is 20) in newly formed protein molecules. Transformations of any part of the DNA molecule lead to a change in the protein composition of the organism and ensure the adaptation of the species by natural selection to new living conditions. Each species usually has a constant number of pairs of chromosomes from 16 to 240. With the development of a new organism, any pair of its homologous (externally similar) chromosomes (diploid set) is included in the chromosome (haploid set) from each parent. The chromosomes of each pair are thus different from the chromosomes of all other pairs. With two pairs of chromosomes, as a result of divisions of maturation, four types of gametes are formed (in females and males). Adding one pair of chromosomes each time doubles the number of chromosome combinations. As a result, the number of gamete types is In, and the number of different zygotes (after fertilization) is 4n, where n is the number of pairs of chromosomes. With 24 pairs of chromosomes. the number characteristic of many species of fish, the number of individual gametes will exceed 16 million, and zygotes (in one crossing). 250 trillion.
The problem of closely related breeding (inbreeding) and its extreme manifestation. incest (mating of producers with their offspring) is that descendants inherit from their parents the same properties (harmful and beneficial), which with further breeding in themselves increase (homogeneity). The genetic material obtained from non-identical parents ensures the diversity (heterogeneity) of future generations, i.e., the effect of heterosis. a hybrid force will constantly manifest itself. As can be seen from previous mathematical calculations, the danger of inbreeding for fish is greatly exaggerated. However, outbreeding (periodical, once every 3-5 years, crossing with unrelated producers) and optimal conditions for keeping and breeding allow it to be completely removed.
Dominant (strong) signs always prevail over recessive (subordinate). When crossed in the first generation, all individuals will have the dominant type. Only with further dilution we get 25% of purebred dominants. 50% of crossbred, but with a dominant trait, and 25% of purebred recessive individuals, which visually looks like a 3: 1 split. Selection by two signs gives a distribution of 9: 3: 3: 1.
The culling of individuals deviating from the desired breeding type must be rigid. Fry that have a worse exterior than their parents are removed from the aquarium. A hybrid is the end product of the crossing of at least different species, while a cross is the result of the breed merging. In practice, the following forms of crossing are used:
1. Industrial (mass). ensures the growth of diversity, but does not consolidate the breed.
2. Synthetic crossing, which allows you to combine the desired characteristics of the original rocks and at the same time increases the heterogeneity.
3. Introductory crossing. contributes to the improvement of the breed by enhancing ce on a new improving hetenic material.
4. Absorption. after the initial crossing of two breeds, a mixture of hybrids with individuals of the breed-improver is carried out.
5. Alternative crossing. alternately mating of hybrids after the first crossing with individuals of 1, two original breeds, in the fourth-fifth generations is replaced by reproductive crossing, stabilizing the desired traits as a result of breeding in oneself.
An additional and very significant source of fish variability are mutations. changes in chromosomes and genes. Mutant genes responsible for steel coloration and albinism reduce the viability of pure lines. Influencing hard radiation and chemical compounds (nitrosmethylurea. 0.97. 9.7 mM (millimole), dimethyl sulfate. 0.11-0.13 mmM, etc.), artificial mutations can be caused. They are classified into point (gene), chromosomal rearrangements (inversions, translocations, etc.) and polyploidy (the presence of one or more additional gene sets). The patsiliopsis (P. turrubarensis), for example, has a triploid set of chromosomes. The multiplicity of larvae leads to cold and exposure to cytochalasin.
When determining the sex of fish, it turned out that guppies, petsilya sphenops, medak, etc. belong to the type XX-XY (male heterogametic). A Xiphophorus maculatus has both male (XY) and female heterogametosis (WY) and even three types of sex chromosomes (WY, WX, XX).
Different lines of Mozambican tilapias have heterogametic behavior of females and males. The crossing of these lines led to the formation of some males in the progeny. In green swordtails (X. helleri) and black macropods (M. orecularis concolor), sex differentiation depends on male and female hereditary factors located in the autosomes (there are no sex chromosomes).
It has long been noted that females of fish under the influence of certain conditions (environment, hormonal preparations, etc.) turn into males (gambusian, melanochrome, etc.). The female sex hormone (estrol) and the male (methylhestosterone) add water to the food or redefine the sex. The Japanese geneticist Yamamoto turned the goldfish females into males. With further breeding, all offspring turned out to be female. In a guppy, females with fins of males are sterile.
Aquarists bred about 200 species of aquarium fish (angelfish, goldfish, Betta Fish, viviparous fish, barbs, etc.). Often very effective offspring is obtained by hybridization of short-tailed kartozubyh, tsikhlovyh, gambuzievyh, cyprinids, etc. As a result of “reprehensible” inbreeding (constant crossing of one-litter fry obtained from a single pair of producers), in the 4-6th generations a lot of albinos appear (labo, swordtails, minor, neon, stirella, Aripirang nanno-stom, petilia, Gambian barbs, oligolepis and sumatranus, speckled catfish, plecoste, guppy, pseudo-trophus zebra, etc.), veils (heteromorph, hasemania, ternation, cardinal, danios, fiery barbus, scalar) and chromic forms (chichlasomes, barbus) "mutant", parrot cichlid, etroplus, thyl Japan aurea, labeothropheus, etc.).
Fish growth can be significantly accelerated by intramuscular injections (mg / kg): bovine growth hormone or bovine insulin (10), 4-chlortestosterone acetate (0.5), thyroidin (10), testosterone propionate (10), methyandandrostenediol (4 mg / kg every 4 days); or with the addition to the feed (mg / kg): ethylestrol (2.5), 17-methyl-testosterone (1-2), dimethazine (5), 17-ethynyltestosterone (2.5-3.5), methylandrosterone (15), androstedione (500), testosterone propionate (560), androsterone (580), dehydroepiandrosterone (3200), testosterone (10), oxymetholone (10), 11-ketotestosterone (10), stanazole (833), thyroidin (60) , 1-dehydrosterone acetate (15), dry thyroid (6), krezacin (10-20) and triiodothyronine (20 mg / kg). 100% of males can be obtained by adding to the fish food (50 to 100 mg / kg) of methyltestosterone and ethinyl testosterone, and 100% of the females grow when the fry are treated with ethinyl estradiol (50 mg / kg) and estradiol (20 mg / kg). With the help of super-solvents (dimethylsulfaxide), you can enter any hormones, drugs, adaptogens, vitamins, etc. into the fish. no pricks, direct transport of substances through the integument.
Most fish do not care for the roe, putting it off in abundance so that at least part of the offspring can survive. But in a limited aquarium, all caviar can be food for other inhabitants. Some species give birth to live fry, which also become a delicacy. But there are a lot of those who actively take care of caviar and fry. These include, for example, cichlids. However, their strict adherence to their territory often turns into a tragedy for other fish. Caring for some species can also cause injury. That is why, if you seriously decided to start breeding fish, do not let this process take its course. And for breeding pairs, as a rule, a separate aquarium is needed.
If the requirements for the chemical composition of water in a normal aquarium may not be too hard, then for the inhabitants breeding aquarium. "maternity hospital" should be created optimal conditions. Otherwise, the caviar will not turn out. There are species with seasonal reproduction. such spawning requires triggering signal-effects that mimic natural phenomena: rain (frequent water changes), provision of food, improvement of its quality (abundance of live food) and temperature increase. Fish living in cold and temperate climates can respond to the length of daylight. Some species require a special substrate for laying eggs (surface or material in which caviar is deposited). All these conditions are easier to accomplish in a separate breeding aquarium , which must meet all the other usual criteria.