Maturity scales (for simultaneously spawning individuals):
1) juvenile(juv) individuals (immature), the sex is indistinguishable to the naked eye. The gonads look like thin threads;
2) preparatory: the gonads begin to mature, the sex is distinguishable, the stage in most fish continues throughout the summer;
In females, the ovaries look like transparent cords along which a blood vessel runs. The eggs are not visible to the naked eye.
In males, the testes have the appearance of flattened cords and are pinkish-whitish in color;
3) maturation: the ovaries increase in volume; spring-spawning fish can remain in this stage from the second half of summer until the spring of next year.
In females, the eggs are clearly visible to the naked eye, have a multifaceted shape, and are difficult to separate when scraped. Their transparency decreases and towards the end of the stage they become opaque.
In males, the testes have a more widened anterior part, tapering at the back. At cross section their edges do not melt;
4) maturity: genitals reach almost maximum development (short stage)
In females, the ovaries usually fill 2/3 of the abdominal cavity. The eggs are large, transparent, easily separated from each other, and flow out when pressed.
Males have testes white and are filled with liquid milk; when the testis is cut transversely, its edges are rounded. When pressing on the abdomen, drops of sperm are released, often with blood;
5) spawning(fluid)
In females, when light pressure is applied to the abdomen, eggs are released.
In males, light pressure on the abdomen releases sperm;
6)knockout: reproductive products are completely swept out (short stage)
In females, the ovaries are flabby, inflamed, and dark red in color. Often a small amount of eggs remains.
In males, the testes are flabby, inflamed, and dark red in color;
6-2) Recovery stage- the gonads are restored after spawning and acquire an elastic shape, but the areas of the ovaries and testes near the urogenital opening remain inflamed.
Advantages:
Used in field conditions in PBA
Allows clear identification of intraspecific dynamics
Flaws:
Subjectivity
Quantitative indicators:
The maturity coefficient is the ratio of the mass of the gonads to the body mass of the fish, %
Maturity index is the percentage of gonad CV, calc. in certain periods of gonad maturity to max KZ.
54. Fish fertility: basic concepts and methods for their detection.
Fecundity varies with age and environmental conditions.
Absolute fecundity (individual) - the number of eggs that a female can spawn in 1 spawning season.
With increasing body weight and size, fertility increases
Relative individual fertility is the number of eggs per unit mass of the female.
Working fertility is the number of eggs taken for the purpose of reproduction from 1 female.
Species fertility is the number of eggs spawned by a female during her entire life.
Population fecundity is the number of eggs that are spawned by a population in 1 spawning season.
Method for determining fertility
Taken at stage 4 of maturity.
It is taken by weight or volumetric method.
Determine fertility by portions
Analyze the eggs and select portions.
55. Features of determining the stages of maturity and fertility in portion-spawning fish species. Fecundity is the number of eggs that a female can spawn in one spawning season. In portion-spawning fish, fecundity is determined by the number of portions; if a fish spawns 2-3 portions, it can be determined by a visual method; if >3 portions, histological studies must be done. Degree of gonad maturity methods: 1) histological (sections are made and the degree of maturity of the oocyte and sperm is determined), 2) maturity scale (juvenile, preparatory, maturation, maturity, spawning, hatching), 3) quantitative indicators of gonad mass and body weight of the fish. For the ovary of fish with spawning periods, it is typical: undeveloped oocytes or oocytes of different phases of maturity. Each portion can precede the other by 2-3 weeks. The portion size is judged on the basis of measuring the diameter of the eggs in the ovary during the pre-spawning and spawning periods.
For the successful implementation of fish farming and reclamation activities, in-depth knowledge is required life cycle valuable species of fish and the most important link - reproduction.
Concept fish breeding includes: development of the gonads, spawning, fertilization, embryonic and postembryonic development. Reproduction is possible only when the fish reach sexual maturity, i.e. maturation of their reproductive products (in females, eggs, in males, sperm).
Sexual maturity in certain fish species occurs at at different ages. Most carp, perch salmon fish reach sexual maturity at 6-12 years. In some fish species, the period of development of germ cells is delayed by more than long time. Thus, sturgeon reach sexual maturity at 6-12 years (beluga - 10-16 years). Sexual maturity in males occurs 1-2 years earlier than in females.
Environmental factors (primarily temperature and nutritional conditions) have a great influence on the process of maturation of fish reproductive products. Low temperatures, as well as insufficient nutrition, can stop the maturation of the gonads. Normal maturation of germ cells - oogenesis in females and spermatogenesis in males - occurs only under favorable environmental conditions. Each germ cell, before it finally matures, must go through a number of stages in its development. In this case, two processes are distinguished: 1 – the period of reaching sexual maturity, starting from the emergence of primary germ cells and ending with the formation of mature reproductive products; 2 – periodic maturation of a certain part of the reproductive products during the interspawning period (after reaching sexual maturity). The first period is longer, the second takes different times for different fish species. Thus, carp and bream reproduce annually, but sturgeon fish die after 3-5 years, and Pacific salmon die after spawning.
The stage of maturity of the gonads can be determined using maturity scales. For carp and perch fish there are S.I. scales. Kulaev and V.A. Meyen, for sturgeon - A.Ya. Nedoshivina, A.V. Lukin and I.N. Molchanova. O.F. Sakun and N.A. Butskaya developed two universal scales for all commercial groups of fish. Based on these two scales, a single universal scale of maturity of the gonads of females and males has been developed.
Development of female germ cells (oogenesis) consists of the following stages:
Stage I – immature young individuals. The gonads look like thick transparent cords adjacent to the walls of the body cavity. Reproductive cells in females are represented oogonia, or young oocytes during the period of protoplasmic growth.
Stage II – maturing individuals, or individuals with developing reproductive products after spawning. The ovaries are translucent. Along them runs a large blood vessel. When viewed through a magnifying glass, the ovaries are clearly visible oocytes period of protoplasmic growth. Individual oocytes have already completed growth and can be distinguished with the naked eye. A layer of follicular cells formed from the germinal epithelium of the ovaries is formed around the oocytes.
Stage III - the gonads are far from maturity, but are already relatively well developed. The ovaries occupy from a third to half the volume of the abdominal cavity and contain small opaque oocytes, visible to the naked eye, usually different shades yellow color. When an ovary ruptures, several lumps form. At this stage, oocyte growth occurs not only due to protoplasm, but also as a result of the accumulation of nutrients in the plasma, represented by yolk granules and fat droplets. This period is called period of trophic growth(large) .
Depending on the pigment specific to different fish species, the ovaries acquire a different shade. Vacuoles containing substances of carbohydrate nature appear in the cytoplasm of oocytes. The oocyte membrane is formed. First, microvilli form on the surface of the oocyte. A thin layer of homogeneous structureless material is formed at the base of the microvilli. With the accumulation of yolk inclusions in the oocyte, another layer is formed, consisting of bundles of tubular structural elements. Then the inner layer transforms into a homogeneous outer layer, and both layers form a single shell. Depending on the biology of the species and the ecology of spawning, adaptability during phylogenesis and other conditions, the shell of different fish species has a different structure. So, in sturgeons it consists of several layers (complex shell), in some species it is one layer.
When examining the oocyte membrane under a microscope, radial striations are visible, hence the name zona radiata.
An oocyte with a formed zona radiata is surrounded by follicular cells, which form the follicular membrane, or follicle. In some fish species, another shell (jelly) is formed above the zona radiata, for example, in roach. Some fish species have a villous shell.
Stage IV - the gonads have reached or almost reached full development. Oocytes are large and easily separated from each other. The color of the ovaries varies among different species of fish. Usually it is yellow, orange, in sturgeon it is gray or black. Germ cells are represented by oocytes that have completed trophoplasmic growth and have formed membranes and micropyle. At stage 4, as well as at stages 2 and 3 of maturity in polycyclic fish, the ovaries contain oogonia and oocytes of the period of protoplasmic growth, which form a reserve for future spawnings.
The egg shell contains a micropyle for sperm to penetrate into the egg. Sturgeons have several of them (this is a species adaptation). The oocyte nucleus moves toward the micropyle. The kernel and yolk are located polar. The nucleus is at the animal pole, the yolk is at the vegetative pole. The yolk merges with fat.
Stage V – fluid individuals. The eggs flow freely from the genital opening. When transitioning to stage V, the eggs become transparent. When the follicle ruptures, the egg subsequently enters the oviduct or abdominal cavity, depending on the structure of the ovary. After ovulation, a rapid maturation process occurs - meiosis.
In sturgeons, the kernels of the nucleus dissolve and the nucleus decreases in size. The shell of the nucleus dissolves and divisions begin. After this, the fish oocytes are released from the follicular membrane.
Stage VI – spawned individuals. The reproductive products have been swept out. The ovaries are small, flabby. The remaining follicles, as well as unspawned eggs, undergo resorption. After the empty follicles are reabsorbed, the ovaries enter stage II, and in some cases, stage III of maturity.
The considered scale of stages of maturity of the gonads can be used in the analysis of fish with one-time spawning, in which females spawn only once a year. However, in some fish species spawning is portioned (many carp, herring and perch). Females of such fish spawn several times during the year; their oocytes mature at different times.
Process development of male germ cells (spermatogenesis) includes several stages:
Stage I. Male reproductive cells are presented spermatogonia. Spermatogonia are primary germ cells that are formed in male fish from the peritoneal epithelium.
Stage II. The testes look like flat cords of grayish or white-pink color. Sex cells are represented by spermatogonia in a state of reproduction. They divide several times, increasing in number, from each initial one five are formed (such groups are called cysts).
Stage III. The testes at this stage increase significantly in volume, they are dense and elastic. Spermatogonia enter a period of growth and turn into spermatocytes I order. Then they begin to divide and from each first-order spermatocyte, two second-order ones are obtained, and then 4 spermatids smaller size. The resulting spermatids enter a period of formation and gradually turn into mature sperm.
Stage IV. The testes at this stage are largest in size and milky white in color. At this stage, spermatogenesis is completed and the seminiferous tubules contain sperm.
V stage. Seminal fluid is formed, leading to liquefaction of the mass of sperm, causing them to leak out.
VI stage. Spawned individuals. The testes are small and flabby. The remaining sperm are exposed phagocytosis.
Receipt mature producers, in which eggs and sperm are suitable for fertilization, is the most important element of the work on artificial breeding of sturgeon.
Previously, obtaining such fish was only possible near natural spawning sites or directly at spawning grounds, where special fishing had to be organized. Of the caught fish, only a small part (no more than 1-4%) had mature caviar and sperm.
With such an unreliable method of obtaining mature products, organizing artificial breeding on a large scale became extremely difficult.
Ecological and physiological methods of stimulating the maturation of reproductive products
To transfer sturgeon breeding to a planned basis, it was necessary to master the process of transferring producers to the spawning state in order to obtain mature eggs and the same sperm.
There are two ways to solve this problem. One of them - environmental - was developed by Academician of the Academy of Sciences of the AzSSR A. N. Derzhavin. He believed that when breeding sires, environmental conditions should be created that correspond to the natural ones in which the development of reproductive products occurs. Since in nature, eggs and sperm ripen during the fish’s spawning run against the flow of water, A. N. Derzhavin considered this factor to be the main one influencing the acceleration of the maturation of reproductive products. He recommended using oval cages 25 m long, 6 m wide and up to 1.2 m deep for keeping and obtaining mature spawners, in which a current was created and river conditions were simulated (fast currents, etc.). Pebbles are placed at the bottom of such cages. The water supply in the cage is mechanical, water flow is 20 l/s. Improving water circulation is achieved by installing a 19 m long concrete wall in the middle part of the cage along its length. 50 fish are placed in each cage; females and males separately. Along with the current, favorable temperature and oxygen conditions are created in the cages. However, experience with such cages has shown that only one third of the spawners mature in them, and it is also difficult to determine the moment when to take caviar.
The physiological method of stimulating the maturation of reproductive products, developed by Professor N. L. Gerbilsky, does not have these shortcomings. It is based on the introduction of an acetonated pituitary gland preparation into the body muscles of the female and male from whom they want to obtain mature eggs or sperm.
Studies have shown that in the fish body an important regulator of the maturation of germ cells is the brain appendage - the pituitary gland, which connects the body's nervous system with the gonads. The pituitary gland, an endocrine gland, produces special substances - hormones, under the influence of which the producers transition into a spawning state.
The pituitary gland consists of two parts: the cerebral - neurohypophysis and the glandular - adenohypophysis. Gonadotropic hormones are produced by glandular cells of the adenohypophysis.
The best results are obtained by combining ecological and physiological methods of stimulating the sexual function of sturgeon producers. The combination is carried out in the following sequence: first, the breeders are kept in special reservoirs, and then a pituitary injection is made.
Jigging farms for keeping producers
Producers are kept in special reservoirs intended for jigging fish. There are two main types of jigging farms. One of them was designed by prof. B. N. Kazansky, the second - by Kura fish farmers (Kurin type cage farming).
Beregovoe jigging farm designs by B. N. Kazansky. The cage farm designed by B. N. Kazansky has earthen ponds for long-term reserve and concrete cage-pools located near them, intended for short-term maintenance of breeders.
Females and males are kept separately.
The earthen pond consists of two parts: the main, expanded one, with a depth of up to 2.5 m, and a narrowed, shallower part with a depth of 0.5-1 m. In this part of the pond, conditions are created that simulate the approach to the spawning reach. In the expanded part with greater depth, conditions approach those of wintering pits.
The pond for females has the following dimensions: length 130 m (widened part 100 m and narrowed 30 m), width 20-25 m in the widened part and 4-6 m in the narrowed part. The bottom of the expanded section is earthen, and in the narrowed section it is paved with small smooth cobblestones on depleted concrete; Pebbles are scattered at the junction of the widened and narrowed parts.
The water supply to the ponds is mechanical; the water inlet is in the form of a reinforced concrete tray or pipe. Water is discharged through a drainage structure, which ensures both complete drainage of the pond and the ability to drain various water levels. The water level is regulated by sanders. The constant water flow of 30 l/s can be increased to 300 l/s.
Kura type cage farming. It is an earthen pond measuring 75x12 m, divided into three sections using a concrete partition structure, in the middle of which there is a hole for installing a shutter.
In the first section, 105 m long and 3 m deep, the producers are kept for a long time - from 1 to 1.5 months. Filling with water lasts 10-12 hours, and dumping lasts 5-6 hours.
When spawning temperatures approach, the spawners are transferred to the second area, which is an oval concrete pool with vertical walls. In a pool 7 m long, 5 m wide and 1 m deep, preliminary short-term holding of females and males is carried out before injection (1-3 days). The transition from the first to the second section is carried out in the form of a smooth ascent: fishing gear - drags, which are used to catch spawners, are pulled along special guides by electric winches with remote control. The second section is filled with water in 30 minutes.
At the third site, the producers are injected and maintained after the pituitary injection. This area has 2 concrete pools with vertical walls. The length of the pool is 5 m, width 3.5, depth 1 m. It takes 15 minutes to fill and discharge water. There is a canopy over the pool. The transfer of breeders from the second to the third section, as well as their delivery to the operating department, where caviar is obtained, is carried out by a self-propelled electric hoist in cradles.
In early spring, warmer water is supplied from the settling tank, which allows fish to be injected into a more early dates. Producers stay in the pools for 1-3 days. The supply and discharge of water from the pools are independent. Water is supplied using a pipe (flute) located across the pool. Jets of water from the flute are directed in opposite directions. As a result of this water supply, the oxygen regime improves.
50 breeders of beluga, 80 of sturgeon or sturgeon, and 100 of stellate sturgeon are planted in the pool. Water consumption in the pools is 30 l/s. The third plot is enclosed by a picket fence, around which trees are planted.
Harvesting manufacturers
For more effective use producers in fish farming great importance has knowledge of intraspecific biological groups.
The study of stocks of individual fish species made it possible for Acad. L. S. Berg established the presence of intraspecific biological groups in some of them. Further development of this issue belongs to prof. N. L. Gerbilsky.
The doctrine of intraspecific biological groups is based on the recognition of the fact of intraspecific biological diversity inherent in all species of animals and plants. In fish, it is associated primarily with the process of reproduction and can be established by knowing the timing and location of spawning, differences in the sexual cycle, spawning temperatures, the condition of the spawners during the period of their entry into the rivers, and the length of stay of the spawners in the river before spawning.
Biological analysis of the sturgeon stock makes it possible to select the correct location of fish hatcheries, helps to determine the timing of jigging and keeping the spawners, as well as to resolve the issue of the possibility of obtaining mature reproductive products from them in the lower reaches of the river and double use of ponds for rearing young fish during one growing season. Knowing the intraspecific biological groups, it is possible to establish a seasonal schedule that allows for the most rational use of reservoirs and equipment of fish farming enterprises.
As an example, let us give the biological groups of the Kura sturgeon.
Professors N.L. Gerbilsky and B.N. Kazansky found that when sturgeon sires of different biological groups are crossed, its vitality during the embryonic period increases.
The author found that juveniles obtained from crossing sturgeon sires of different biological groups are superior to juveniles from parents belonging to the same biological group in many important fish farming indicators: they feed more intensively and grow faster, they have a higher fatness index, a higher protein content and ash elements.
Procurement of sturgeon spawners belonging to different biological groups for fish farming purposes is carried out at different times.
Thus, early spring sturgeon is harvested in the Volga delta in the second half of April - early May and is used to obtain mature sexual products after a short-term reserve in May. Winter sturgeon of the autumn run is harvested in October, and caviar and sperm are obtained from it after a long period of aging in the second half of April of the following year.
- females close to ovulation have a thin body, while in less mature fish it is very thick and oily;
- in mature fish, the caudal peduncle (from the posterior edge of the dorsal fin to the beginning of the caudal blade) has an oval cross-section, i.e. its height is significantly greater than its width, which indicates that the fish is losing weight. In less mature fish the caudal peduncle is thicker and less high;
- in mature individuals the snout is pointed as a result of weight loss, in less mature fish the snout and entire head are thicker;
- The bugs of mature fish are less sharp, the skin is more covered with thick mucus.
In order to focus on these signs, you need to have extensive experience working with manufacturers.
A.E. Andronov (1979) developed a method for selecting female sturgeon, based on measuring eggs. Among the female stellate sturgeon migrating into the river, there are many insufficiently mature fish, in the gonads of which there is a lot of low-quality small caviar, so it is necessary to select females with the largest caviar. Eggs are measured using a probe that has a scale with a division value of 2 mm and a zero mark at a distance of 31 mm from the beginning of a slot with a diameter of 3 mm. In females selected for fish farming purposes, 15 eggs should form a row ending at least on the second division on the probe scale.
The second option for selecting stellate sturgeon females is to determine the degree of polarization (extreme position) of the nucleus. The caviar removed with a probe is placed in Serra liquid (6 parts formaldehyde, 3 parts alcohol, 1 part ice acetic acid), washed with water and cut with a safety razor along the animal-vegetative axis.
The position of the nucleus in the eggs is assessed under a 7×10 magnifying glass by the distance from the nucleus to the shell of the animal pole. Female stellate sturgeon are considered good if their nucleus has moved away from its original position to a distance not exceeding the radius of the egg.
Researcher at the Azov Research Institute of Fisheries L.V. Badenko has developed a method for selecting producers based on physiological indicators, which makes it possible to more objectively judge the value of producers for fish farming purposes. The method is based on the fact that sturgeon during spawning migrations enter rivers in different physiological state. This is explained both by the unequal maturity of reproductive products and different levels accumulation of reserve substances in their bodies. Thus, according to L.F. Golovanenko, exhausted breeders that are not suitable for obtaining caviar and sperm, as well as individuals that have sexual products in the IV incomplete stage of maturity, need to be reserved, and fish in the IV completed stage can be injected immediately after harvesting at mining sites.
It is clear how important it is to assess the broodstock selected for fish farming. This is most easily done through a blood test. It turned out that the most clear answer to the question about the quality of producers can be given by indicators such as hemoglobin content and serum protein composition. Based on them, L.V. Badenko recommends selecting producers.
At the beginning of the spawning run, females have a significant level of fat and protein, they have high rates of metabolism and respiration, so such fish must be harvested first. They usually have the levels of fat, protein, metabolism and respiration characteristic of fish that produce fully mature eggs.
The preparation is made from seine catches, selecting producers with an optimal weight for work (no more than 15-20 kg for sturgeon and stellate sturgeon and 100 kg for beluga), without injuries, bruises, etc.
When determining the mass of fish, it is prohibited to weigh selected producers on decimal scales at the receiving point, since weighing without water negatively affects the condition of the fish. Weight should be determined using a special table that provides data on the ratio of body length and weight.
The age selection of producers is also of great importance. According to A.A. Popova, the best offspring are produced by sturgeons that come to spawn for the second and third time.
Producers are prepared in such a way as to have a reserve in case of waste during transportation and aging: for beluga and stellate sturgeon from 20 to 30% and for sturgeon from 10 to 30% of total number prepared manufacturers.
Producers are selected directly from the landing seine. One at a time, they are carefully placed on a canvas stretcher and transferred to a small live-fishing vessel (mattenka), into which no more than 10 individuals can be collected. The mother is delivered to a large live fish vessel, in which the producers are transported to the sturgeon hatchery. In a non-self-propelled live fish slot of the Astrakhan type, 5 belugas or 10 sturgeons, the same number of thorns or 16 stellate sturgeons are planted. The length of the Astrakhan type slot is 13 m, width 5 m and depth 0.8 m, loading rate: one sturgeon per 1.5-2 m 3, one sturgeon per 1 m 3 and one beluga per 5-7 m 3. To prevent injury to fish, the slot frames are covered with planed boards.
The producers delivered to the fish hatchery are lifted to the pier using a special crane with a lifting capacity of 500 kg. The fish are transported in a canvas cradle filled with water, suspended from a metal tubular frame. It is covered from above with a canvas apron.
Once lifted onto the pier, the cradle is immediately installed on a tubular stand in the back of a car or self-propelled chassis and transported to the pond. The cradle can also be moved by electric monorail transport. Then by inclined plane The cradle along with the fish is lowered into the pond. Fish can also be transported and unloaded using a monorail and a cargo hoist. With this method of transportation, the cradle with the producers is removed from the chassis by a hoist, moved over the pond and then lowered. Monorail tracks with electric hoists are also used for intra-factory transportation of manufacturers.
From the ponds of the spawners, they catch them with drags (straining fishing gear) equipped with float and sinkers. The float consists of foam floats placed on the top. Sinkers made of baked clay are attached to the lower frame. Wooden blocks called nags are tied to the ends of the wings. The length of the drag is 40-50% greater than the width of the pond, and the height is 30-40% greater than the greatest depth of the reservoir.
Fish are usually caught in one longitudinal cast. They pull the seine by the edges on both sides of the reservoir. The sinking is carried out in a shallow area at the head of the pond. The sinking place is strengthened with rock and pebble backfill. A hoist overhead track is connected to this section to mechanize the lifting of producers.
The caught spawners are placed in a cradle or on a stretcher and brought to a hoist, which delivers the fish to cages where the spawners are injected.
After use, the drags are hung on hangers to dry.
Preparation of pituitary glands
Pituitary glands are best harvested in the spring, during the breeding season. At this time, the reproductive products of fish are in the IV completed stage and the maximum amount of hormones accumulates in the pituitary glands.
It is impossible to harvest pituitary glands from spawned fish, since the hormones previously contained in them are completely consumed during the breeding season. The pituitary glands from immature fish cannot be used for harvesting. At the same time, T.I. Faleeva notes that pituitary glands can be harvested in autumn and winter.
To remove the pituitary gland, the skull of a live or fresh fish is opened with a trephine made of steel, which is a metal rod equipped with a handle. A cylinder is mounted on the lower end of the rod, which can be moved vertically along the rod and secured with a screw. At the base of the cylinder there are sharpened and set teeth that cut into the tissue when the trephine rotates. Its diameter is 30 mm. To obtain the pituitary gland from the beluga, large trephines with a diameter of 35-40 mm are used.
The trephine is placed in the middle of the fish's head, behind the eyes. To accurately install the trephine, the cylinder is lifted up to full capacity, as a result of which the lower pointed end of the rod extends beyond the edge of the cylinder. After this, rotate the handle and, after making several turns, lift the rod to avoid destruction of the pituitary gland. Then the trephine is screwed in completely and the cut plug, consisting of bone and cartilage, is removed. A hole is formed in the skull cap, which, if the trephine is correctly installed, is located above the pituitary fossa. To obtain pituitary glands, an electrotrephine, which is an electric drill, is also used, which greatly facilitates and speeds up the preparation of pituitary glands.
The brain and fluid are removed from the cranial cavity. The preparatory operations end here and you can begin to remove the pituitary gland.
The pituitary gland is removed using a Volkmann spoon, which has sharp edges and a long handle, used in surgery. Under no circumstances should you take gland tissue with tweezers, as this can destroy the pituitary gland and make it unsuitable for injection. Using a Volkmann spoon, the pituitary gland can be easily removed and transferred into a vessel. The removed pituitary gland is degreased and dehydrated, for which acetone is poured into a vessel with a well-closing lid (jug). After removing each pituitary gland, the harvester places it in acetone. After all the pituitary glands are removed, they are placed in a new portion of acetone for 12 hours, then it is drained again and a new portion is poured, in which degreasing occurs after 6-8 hours. The pituitary glands removed from the bottle are dried on filter paper.
To treat the pituitary glands, only anhydrous, chemically pure acetone can be used. The volume of acetone should be 10-15 times greater than the mass of the pituitary glands contained in it. Reusing water-saturated acetone is unacceptable.
For long-term storage, dried pituitary glands are placed in plastic bags and labeled.
It is advisable to select pituitary glands of the same mass into separate bags so that in field conditions at a fish hatchery it is possible to accurately calculate the dosages used.
Procurement of pituitary glands should be carried out centrally for several plants at once with the determination of the gonadotropic activity of the produced drug using test objects.
Centralized procurement by experienced specialists allows us to ensure high quality pituitary glands and the possibility of using optimal doses.
Determination of the quality of pituitary glands
To determine the amount of hormones located in the pituitary glands and the quality of the resulting drugs, biological testing is carried out, which boils down to elucidating the various reactions of the organs of animals that received an injection of the drugs under study. Typically, loaches and frogs are used for biological testing.
After the injection of the pituitary gland, the loach always gives a quantifiable, clear reaction. The determination of the unit of activity of the pituitary gland of fish is carried out using the concept of loach unit (v.u.) established by B.N. Kazansky.
Loach unit- this is the amount of gonadotropic hormone that is necessary to cause, 50-80 hours after injection, the maturation of eggs and ovulation in winter female loaches of stage IV of maturity weighing 35-45 g at a water temperature of 16-18 ° C in laboratory conditions.
In order to determine the activity of the test pituitary preparation in loach units, several groups of females are simultaneously given pituitary injections with different doses of pituitary gland. The smallest dose that caused ripening corresponds to the loach unit. Knowing it, you can compare the content of gonadotropic hormone in different pituitary glands.
The use of loaches as test objects is difficult due to the limited distribution of their distribution in natural bodies of water.
A more accessible object are frogs. They can easily be obtained in the required quantities at any time of the year. A positive reaction in frogs is the appearance of motile sperm in the cloaca after the injection of a suspension of the pituitary gland into the dorsal lymphatic sacs. This reaction occurs very quickly - after 40-50 minutes. This is the second advantage of working with frogs compared to loaches.
Male frogs are harvested in late autumn in places where they are concentrated for wintering. They are kept in water at a temperature of 1.5°C, low flow and low light.
Testing of the drug should be carried out annually at the same time. So, in the Volga delta they do this in the first half of March.
Frogs are brought out of the winter state by slowly raising the water temperature and bringing it after a week to 16-18°C. Testing gives best results at temperatures of 18-23°C.
The check is carried out as follows. First, batches of 8-10 pituitary glands, differing in color and size, are selected. They are then weighed on an analytical balance with an accuracy of 0.1 mg. The weighed preparation is ground in a mortar, gradually moistening until a homogeneous creamy consistency is obtained. Then saline solution is added to the preparation, and the suspension is ready for injection.
The injection is carried out simultaneously in 5 frogs. A total of 3 groups of frogs are tested. Each group is injected with a certain dose: 0.2; 0.3 and 0.4 mg of dry preparation of the pituitary gland.
An indicator of the biological activity of the test pituitary preparation is the minimum weight dose that causes a sperm reaction in more than half of the injected frogs. The biological activity of the drug is calculated by dividing the unit by the weight indicator of the minimum effective dose.
One frog unit(l.e.) is the activity of the minimum weight dose of the drug that causes spermation in a male frog.
The acetonated pituitary gland preparation should have a standard, previously known activity, which is equal to 3.3 frog units.
Using the drug will allow you to use the harvested pituitary glands more economically. In addition, in cases where, after a pituitary injection, maturation of producers is not observed, the analysis of the causes of this phenomenon is facilitated.
It should also be borne in mind that the dose of the administered drug per unit mass of the producers must be calculated taking into account the biological activity of each given batch of pituitary glands.
In addition to the above method for determining the activity of acetonated pituitary glands, there are several other methods for such testing. In particular, B.F. Goncharov proposed using the system of maturation of eggs outside the body to determine the quality of the pituitary glands. The check is carried out as follows. A sample of caviar is taken with a probe and placed in a physiological solution with a 0.1% solution of crystalline albumin. A suspension of the pituitary gland is also added there. If the female is prepared for maturation, then the embryonic vesicle dissolves.
The advantages of the proposed method are that it is sensitive, makes it possible to obtain large digital material, and it can be used directly at fish hatcheries during the season of work with producers.
With this method, the dose of the injected pituitary gland is calculated in milligrams of acetonated pituitary gland per 1 kg of the producer's weight or in milligrams per male or female.
The correct dosage largely determines the quality of the resulting sexual products. If the dose is insufficient, maturation of the breeders will not occur. With an increased dose hormonal drug the quality of eggs or sperm decreases.
At lower temperatures (within the spawning temperature range), higher doses of the drug are required for the maturation of spawners; at temperatures close to upper limit spawning temperatures, the amount of the hormonal drug decreases. To mature males, compared to females, less hormonal medication must be administered.
Sturgeon hatcheries receive acetonated pituitary glands with predetermined gonadotropic activity. However, it does not always remain constant. When pituitary glands are stored for more than a year, their gonadotropic activity decreases. The process of deterioration in the quality of pituitary glands is slowed down when they are stored in a hermetically sealed container in a dry room at a low temperature.
Pituitary injection
The dried pituitary gland is ground into powder with a pestle in a clean glass or porcelain mortar, then the required dose is weighed on an analytical or torsion balance for each batch of injected producers separately for females and males.
A weighed dose is added to a physiological solution (6.5 g of chemically pure table salt dissolved in 1 liter of distilled water) and ground a little more. Then another portion of physiological solution is added to this mass in such a quantity that there is 2 cm 3 of suspension per manufacturer. Then it is thoroughly shaken several times using a syringe and transferred to a bottle with a wide neck and a ground-in stopper.
Before starting the injection, the contents of the bottle are thoroughly mixed several times. The suspension is injected into the back muscles with a syringe. After the injection, the needle is carefully removed. The skin puncture site is pressed with a finger and then massaged a little. This must be done to avoid leakage of the injected drug.
When the water temperature is 2-3°C lower than the spawning temperature, the dose of the pituitary gland is increased by 30-50%.
Pituitary injections give positive results only upon completion of the fourth stage of maturity of reproductive products in producers. An indicator of this state of the eggs is the displacement of their existing nuclei towards the channel (micropyle), through which the sperm penetrates into the egg.
The fourth stage in males is characterized by the completion of the process of sperm formation. In such males, mature, fully formed sperm predominate.
Good results are obtained with single injections of the acetonated drug. However, sometimes they are not effective enough. This situation occurs when general state producers is deteriorated or the development of eggs is not completely completed. In such a situation, it is sometimes advisable to perform repeated injections of small doses of the drug. However, one must always remember that doses of the pituitary gland preparation increased compared to scientifically based ones lead to a decrease in the quality of the resulting mature germ cells. This is explained by the fact that the acetonated pituitary gland powder also contains hormones that are not directly needed for the maturation of germ cells. As a result, side effects, the body comes into a state of great tension (stress).
The success of pituitary injections largely depends on how the breeders are kept. At all stages of this operation - before, during and after the introduction of the pituitary gland preparation into the fish's body - females and males should be handled very carefully to prevent injury. In reservoirs intended for breeders, there must be a good oxygen regime; females and males should be kept separately. Before injection, they are transferred to small concrete pools or cages, in which they are created optimal conditions in order to ensure the maturation of reproductive products after the introduction of a hormonal drug into the body.
Determining the maturation time of producers
After the introduction of the pituitary gland, the fish begin a maturation period (until mature eggs are obtained), the duration of which depends on the water temperature and the initial state of the females.
A. S. Ginzburg and T. A. Detlaf established that at the same average temperature, the ripening period is always much shorter than the period of embryonic development (4-6 times). It follows that with an increase or decrease in temperature, the duration of the periods of maturation and embryonic development changes accordingly. The identification of such a pattern allowed A. S. Ginzburg and T. A. Detlaff to construct graphs of the probable maturation times of female sturgeons at different temperatures depending on the duration of their embryonic development.
The graphs show curves indicating the time when females can be expected to mature after pituitary injections. Using the graphs, you can also determine the timing of viewing females and taking samples by first calculating the average temperature during the maturation period.
The calculation is made as follows. At 19:00 on the eve of the day of receiving eggs and at 7:00 in the morning on the day of collection of eggs, the average temperature is calculated, starting from the time of injection of the spawners. Then on horizontal axis find a point corresponding to the average temperature during the ripening period and restore a perpendicular from it until it intersects with the curves. The point of intersection with the curve shows how many hours later the first females mature. The resulting number of hours is added to the injection time and the start time of viewing females is determined. The point of intersection with the curve makes it possible to determine the timing of maturation of many females in the same way.
Using this schedule, it is possible to determine the timing of injection of a suspension of pituitary glands into female sturgeons in order to obtain caviar at a time convenient for work. As a result, work with producers is facilitated, the number of necessary viewings of females is reduced, the quality of caviar is improved, and losses as a result of its overripening or underripening are reduced.
When calculating the required indicator, first determine the average temperature the day before the injection. Then, on the horizontal axis of the female maturation graph, a point corresponding to this temperature is found, and a perpendicular is restored from it until it intersects with the curve. From the intersection point, a perpendicular is lowered onto the vertical axis and the number of hours that will pass at a given average temperature from the injection to the maturation of the first females is determined from it. The number of hours calculated in this way is subtracted from the start time of the working day and the time when the females need to be injected is obtained.
A method for determining the degree of maturity of the female gonads without opening the fish was also proposed by V.Z. Trusov. This method boils down to removing several eggs from the female ovary using a probe. They are transferred with tweezers into a test tube with formaldehyde. The tubes are brought into a room where a freezing microtome is installed. The eggs are placed on the table so that the microtome razor sections pass through their animal and vegetative poles. Then the eggs are poured with water from an eye pipette, after which the table is covered with a metal cap and the sections are frozen by adding carbon dioxide from a balloon.
Sections are made until a core clearly visible to the naked eye or under a magnifying glass appears. If it lies close to the membranes, then the state of the female gonad is in the IV completed stage of maturity.
The method for determining the degree of maturity of the female gonads, proposed by V.Z. Trusov, is relatively simple, reliable and takes little time: analysis of one sample can be carried out in 5-8 minutes.
The maturation of females is also monitored by direct observation. Control is intensified during the last six hours - the most probable period of ripening at a given temperature.
An even simpler express method for determining the maturity of gonads in sturgeon breeders was developed by Prof. B. N. Kazansky, Yu. A. Feklov, S. B. Podushka and A. N. Molodtsov. The essence of the method is that using a probe, a sample of caviar is taken from the back of the ovary; the probe is inserted into the body cavity at an angle of 30°, which allows it to avoid touching vital organs. The dipstick has a tip that is filled with eggs and a rod that allows it to be emptied.
The total length of the probe is 125 mm, the tip is 65 mm, including the pointed part - 20 mm. The outer diameter of the rod is 4.5 mm. The probe ends with a handle located perpendicular to the rod. To determine the degree of completion of the fourth stage of maturity, the eggs extracted with a probe are boiled for 2 minutes. The hardened eggs are cut with a safety razor blade along the axis from the animal pole to the vegetative pole. The sections are examined under a magnifying glass or binocular. The degree of polarization of the egg is determined by the position of the nucleus relative to the animal pole. The polarization index is determined by the formula proposed by Yu. A. Feklov: l = A/B, where l is the polarization index; A is the distance from the core to the shell; B is the greatest distance along the axis from the animal to the vegetative pole.
The lower the value of l, the more polarized the egg is and the more complete the IV stage of gonadal maturity is. The greatest polarization of the oocyte is observed at l = l/30: l/40.
If the female’s abdomen, when palpated, turns out to be softer than it was before the injection, then this indicates the possible maturation of eggs in this individual. To make sure of this, you should bring a fish stretcher with water under the female, lift it and place it on the trestle. At this time, the fish makes sudden movements, and if the eggs are ripe, then the eggs released on the stretcher can be seen. After the female has calmed down, she is turned on her side and her belly is felt. In a mature individual, when the rear third of the belly is massaged, caviar flows out freely in a stream.
Thus, as noted by A. S. Ginzburg and T. A. Detlaf, indicators for opening females are a soft abdomen, eggs ejected in a strong stream, and sinking abdominal wall when the female rises.
It is necessary to immediately obtain eggs from a fully mature female.
Obtaining mature caviar
Work on obtaining mature reproductive products, including collection, fertilization and washing of eggs, is carried out in operating department, which is usually located in the hatchery. It has equipment for obtaining reproductive products, such as a winch, a clamp, and a refrigerator (KX-6B), in which the producers are stored without caviar and sperm (the caviar and sperm are obtained before they are delivered to the procurement point). In the operating department there are production tables measuring 126x84x90 cm, type SPSM-4.
A mature female is stunned with a strong blow to the nose with a wooden mallet, after which she is bled dry by cutting the caudal or gill arteries, washed with water and dried. To prevent blood from getting into the basin with the caviar, the incision site is bandaged. The fish, ready for opening, is lifted by the head through a crossbar or block and secured. The abdomen is incised from the bottom up from the genital opening by 15-20 cm. The incision is made shallow and slightly to the side of the midline. To avoid possible loss of eggs, the female’s tail is held above the pelvis. Part of the ripe caviar flows freely into the basin along its edge. After this, the abdomen is cut to the pectoral fins and the remaining, freely separated eggs are transferred to the pelvis. You can also use benign eggs available in the oviducts for fertilization.
The amount of eggs obtained depends on the weight of the female.
Eggs from different females are not mixed. All operations with caviar are carried out with extreme caution. Caviar can only be collected in basins with intact enamel. No more than 2 kg of caviar is placed in a basin with a capacity of 12-15 liters.
Only full-fledged mature eggs are fertilized, which must be able to be identified.
Unripe eggs differ from mature ones by having the same color in all areas. Ripe eggs discolor very slowly water solution methylene blue. This solution does not discolor unripe eggs at all, but overripe eggs discolor much faster than ripe ones. This method of determining the fish breeding quality of sturgeon caviar was developed by M. F. Vernidub, associate professor of Leningrad State University. It boils down to the following: 2 cm 3 of caviar (without cavity fluid) is placed in a bottle or tightly closed test tube filled with 10 cm 3 of a freshly prepared solution of methylene blue (one drop of a 0.05% aqueous solution of paint per 10 cm 3 of water), several Shake once and take into account the time during which the solution discolors.
In some cases, discoloration does not occur within the usual time frame for caviar of this quality.
Determining the readiness of eggs for fertilization
L. T. Gorbacheva, an employee of the Azov Research Institute of Fisheries, proposed assessing the readiness of eggs for fertilization in a factory by the rate at which the egg shells become sticky after fertilization.
In order to determine when to begin insemination of eggs that have already been removed from the female’s body cavity, 100-150 eggs are taken, inseminated with sperm, and the time during which the eggs in the sample stick to the Petri dish is determined. After this, according to a special schedule, the time is set when all eggs should be inseminated. For sturgeon caviar, the best condition for fertilization is considered to be in which at least 90-95% of all fertilized eggs stick in 9-16 minutes; for sevruga caviar this state corresponds to a time of 6-10 minutes. Such caviar develops normally.
Overripe sturgeon caviar begins to stick after 4-6 minutes, and stellate sturgeon - after 2-4 minutes. Such eggs produce increased mortality during the incubation period.
Only eggs are used for fertilization High Quality, the indicators of which are:
- the presence on the embryonic pole of a spot of a different color than the other half of the egg;
- regular round shape and equal size of eggs, as well as colored blastomeres formed after the appearance of two cleavage furrows;
- appearance after 6-12 minutes in sturgeon and after 5-10 minutes in stellate sturgeon a narrow gap between outer shell and eggs from an egg sample quickly washed from the cavity fluid (in overripe eggs this process begins earlier, in unripe eggs - later);
- a certain mass of eggs; 1 g of mature beluga caviar should contain 35-40 eggs, sturgeon - 45-50 eggs, stellate sturgeon - 75-90 eggs.
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EMBRYOLOGY
Lecture 7
Sex cells in fish are formed in the gonads - sex glands. In accordance with modern concepts, in fish the rudiment of primary germ cells - gonocytes - is separated at the end of gastrulation. Their source is the primary endomesoderm, and the periblast is a temporary refuge before the start of migration into the gonad. It is possible that primary germ cells are present in the gonads of adult fish.
The process of development of female germ cells is called oogenesis. Gonocytes move into the rudiment of the female gonad, and all further development of female germ cells occurs in it. The structure of oogenesis is basically the same in all animals. Once in the ovary, gonocytes become oogonia.
Oogonia is an immature germ cell capable of mitosis. Oogonia carry out the first period of oogenesis - the period of reproduction. During this period, oogonia divide mitotically. The number of divisions is species specific. In fish and amphibians, the periodicity of mitotic divisions of oogonia is associated with seasonal reproduction and repeats throughout life.
The next period of oogenesis is the period of growth. Sex cells in this period are called first-order oocytes. They lose the ability to undergo mitotic division and enter prophase I of meiosis. During this period, the growth of germ cells occurs.
There are small and large growth stages. The main process of the period of great growth is the formation of the yolk (vitellogenesis, vitellus - yolk).
During the period of small growth (previtellogenesis, cytoplasmic growth), the volumes of the nucleus and cytoplasm increase proportionally and insignificantly. In this case, nuclear-cytoplasmic relationships are not disrupted. During the period of great growth (vitellogenesis), the synthesis and entry of inclusions into the cytoplasm are highly intensified, leading to the accumulation of yolk. The nuclear-cytoplasmic ratio decreases. Often the egg during this period greatly increases and its size increases tens of times (humans), hundreds of thousands of times (frogs, fruit flies) or more (shark fish and birds).
The following types of nutrition of egg cells are distinguished:
Phagocytic type - found in the germ cells of animals that do not have gonads (sponges, coelenterates). With the phagocytic method of vitellogenesis, oocytes, moving through the intercellular space, are able to phagocytose somatic cells of the body.
Solitary type - found in colonial hydroid polyps, echinoderms, worms, wingless insects, lancelets. With the solitary method of nutrition, the oocyte receives ingredients from the coelomic fluid and from the gonad. Yolk proteins are synthesized in the endoplasmic reticulum, and the formation of yolk granules occurs in the Golgi apparatus.
Alimentary type - carried out with the help of auxiliary cells; divided into nutritional and follicular.
The nutritional method of nutrition is found in worms and arthropods. In them, the oocyte in the ovary is surrounded by trophocytes (nursing cells), with which it is connected by cytoplasmic bridges. The cell that comes into contact with a large number of sister cells (nurse cells) becomes an oocyte. The follicular mode of nutrition is found in most animals. The auxiliary cells in this method of nutrition are the gomatic cells in the ovary. The follicle, i.e., the oocyte along with auxiliary follicular cells, enters oogenesis. The bulk of the yolk is formed due to the intake of substances from the outside, and oocytes with exogenous synthesis of yolk grow at high speed. In the surface zone of the oocyte, many pinocytic vesicles appear containing vitellogenin, a precursor of yolk proteins coming from the blood.
Vitellogenins in different animals are synthesized in different somatic tissues and, in the process of evolution, are gradually concentrated in a strictly defined organ. In vertebrates, vitellogenin is produced by the liver of females. Vitellogenin is synthesized by liver cells and is under hormonal control.
To begin the process of embryo development from the moment the egg is fertilized, some preparation for this event is made in the egg itself. The egg nucleus must be brought into the appropriate state in order to unite with the sperm nucleus; in this case, part of the chromosomal material is removed from the egg, turning into small polar bodies (this process is usually not completed by the time of fertilization, but is temporarily suspended). Further, the cytoplasmic contents of the egg become quite high level organization; by this time the nature of its future symmetry appears to have been largely determined, although further events may modify it. The amount of yolk contained in an egg varies greatly; it serves as the main factor determining the size of the egg and the type of crushing. In some animals, in particular the lancelet and humans, the eggs contain little yolk. Such eggs can be called oligolecithal. The other type of egg is somewhat larger and contains a moderate amount of yolk; they are called mesolecithal. Typical mesolecithal eggs include frog eggs; these also include eggs of tailed amphibians, lungfishes, lower ray-finned fish and lampreys.
Mesolecithal eggs are so common among primitive aquatic forms that they were probably characteristic of ancestral vertebrates. Sharks and rays, on the one hand, and reptiles and birds, on the other, have large eggs; they are called polylecithal because most of the cell is occupied by the yolk, and the cytoplasm, which is relatively small, is concentrated at one pole.
Eggs are also classified based on the distribution of the yolk within them. In some eggs, mainly oligolecithal ones, the yolk is distributed fairly evenly throughout the cell; such eggs are called isolecithal. In meso- and polylecithal eggs, the yolk is in most cases concentrated in one half of the egg; for eggs floating in water - in the lower half. Such eggs are called telolecithal. In modern bony fishes, eggs are also very rich in yolk, but their sizes vary.
The concentration of yolk in one hemisphere clearly indicates the presence of a certain organization, or polarity, in the egg: at its upper end there is an animal pole, and at the lower end there is a vegetative one; The upper half of the egg is filled with relatively transparent cytoplasm, and the lower half is filled with yolk.
Fish eggs, like vertebrate eggs, are extremely varied in size; they are, as a rule, spherical cells containing, in addition to the nucleus and a certain amount of transparent cytoplasm, a yolk that serves as food for the developing embryo. Fish eggs are usually spherical, although there are other shapes. The structure of the eggs is characteristic feature not only for genus, family, but also for larger categories.
Fish eggs differ not only in shape, but also in size, color, the presence or absence of fat drops, and the structure of the shell. The size of the eggs is the same as others morphological characteristics, is a stable characteristic of the species. Large fish lay eggs of a larger diameter than small ones, but the amplitude of fluctuations in egg size remains constant for the species even in different water bodies, although their average values may shift in one direction or another.
The size of the eggs depends on the content of the nutrient in them - the yolk and varies significantly (in mm): sprat - 0.8-1.05, carp - 1.4-1.5, grass carp - 2.0-2.5, Russian sturgeon - 3.0-3.5, salmon - 5.0-6.0, chum salmon - 6.5-9.1, polar shark - 80 (without capsule), whale shark - 670 (length with capsule) .
Among the numerous bony fish, the smallest eggs are characteristic of flounder, the largest - for salmon, especially chum salmon. The large volume of yolk in salmon eggs, unlike other fish, provides more a long period development, the appearance of larger larvae capable of consuming larger food organisms at the first stage of active feeding. The largest eggs are observed in cartilaginous fish. The development of embryos in some of them (katran) lasts almost 2 years.
The color of the eggs is specific to each species. In vendace they are yellow, in salmon they are orange, in pike they are dark gray, in carp they are greenish, in greenlings they are emerald green, blue, pink and purple. Yellowish and reddish tones are due to the presence of respiratory pigments - carotenoids. Caviar developing in less favorable conditions oxygen conditions, usually more intensely colored. Of the salmonids, sockeye salmon has the brightest crimson-red caviar, developing in water relatively poor in oxygen. Pelagic eggs, which develop with sufficient oxygen, are poorly pigmented.
The eggs of many fish contain one or more fat drops, which, along with other methods, such as watering, provide buoyancy to the eggs. The eggs are covered on the outside with shells, which can be primary, secondary and tertiary.
The primary - vitelline, or radiate, membrane, formed by the egg itself, is penetrated by numerous pores through which food enters the egg. nutrients during its development in the ovary. This shell is quite strong, and in sturgeon it is two-layer.
Above the primary shell, most fish develop a secondary shell, gelatinous, sticky, with various projections for attaching eggs to the substrate.
At the animal pole of both membranes there is a special channel, the micropyle, through which the sperm penetrates into the egg. Teleosts have one canal; sturgeons may have several. There are also tertiary membranes - albuminous and horny. The cornea develops in cartilaginous fish and hagfish, while the protein membrane develops only in cartilaginous fish. The cornea of cartilaginous fish is much larger than the egg itself, does not correspond to it in shape, is flattened and slightly compresses the egg. Often horny threads extend from it, with the help of which the egg attaches to aquatic plants. In ovoviviparous and viviparous species, the cornea is very thin, disappearing soon after the onset of development.
Parthenogenesis. The development of an egg is possible without the participation of a sperm, and in this case it is called parthenogenesis (from the Greek “parthenosis” - virgin, “genesis” - emergence).
There are cases where organisms develop normally from laid unfertilized eggs.
When they talk about parthenogenesis, they mean development based on the female pronucleus. However, in some cases, development on the basis of the male pronucleus is possible, and then they talk about androgenesis, contrasting it with gynogenesis. Gynogenesis is a form of unisexual development in which the sperm activates the egg, prompting it to develop, but its nucleus (male pronucleus) does not merge with the female one and does not participate in drinking. Natural gynogenesis is known in one species of crucian carp, the eggs of which are inseminated with the sperm of another species, which activates the eggs, but the sperm nucleus does not participate in the formation of the zygote. Androgenesis is a much rarer phenomenon, and when it occurs (natural or artificial), development occurs without the female pronucleus on the basis of the male nucleus and male pronucleus.
Male reproductive cells - sperm in contrast to oocytes, they are small, numerous and mobile. Each group of sperm is a derivative of one initial cell and develops as a clone syncytially connected cells, and in terms of number and some structural features it gives a group of individual motile cells. The development of spermatozoa itself is similar in different animals. Spermatogenesis is always closely associated with auxiliary service cells of somatic origin. The relative position of reproductive and somatic servicing cells quite specifically characterizes spermatogenesis and is of the greatest interest. It is more correct to consider the development of a sperm not as a “biography” of an individual male reproductive cell, but as the life history of a clone.
Male germ cells never develop alone, but grow as clones of syncytially linked cells, where all cells influence each other.
In most animals, auxiliary somatic cells of the follicular epithelium (“supporting”, “feeding”) take part in the process of spermatogenesis.
Germ cells and associated auxiliary cells at an early stage of development are separated from the soma cells by a layer of border cells that perform a barrier function. Inside the gonad itself, further structural separation occurs in the form of cysts or tubules, where auxiliary follicular cells create a specific environment for spermatogenesis.
Primary germ cells, including male ones, in many animals can be identified long before the formation of the gonad and often even at very early stages of development. Germ cells appear early in embryonic development in the genital folds that extend along the body cavity. In juvenile salmon (pink salmon, chum salmon, sockeye salmon, masu salmon, coho salmon and Atlantic salmon), primary germ cells are found at the stage of formation of the primary renal ducts. In the Atlantic salmon embryo, primordial germ cells were identified at the age of 26 days. In fish fry, gonads can already be found in the form of hair-like cords.
Distinctive feature The process of sperm development - spermatogenesis - is a multiple reduction of cells. Each original spermatogonia divides several times, resulting in an accumulation of spermatogonia under one membrane, called a cyst (reproduction stage). The spermatogonia formed during the last division increases slightly, meiotic transformations occur in its nucleus and the spermatogonia turns into a first-order spermatocyte (growth stage). Then two successive divisions occur (maturation stage): a spermatocyte of the first order is divided into two spermatocytes of the second order, due to the division of which two spermatids are formed. In the next – final – stage of formation, spermatids turn into spermatozoa. Thus, from each spermatocyte four spermatids are formed with a half (haploid) set of chromosomes. The cyst shell bursts, and sperm fill the seminiferous tubule. Mature sperm leave the testis through the vas deferens, and then out through the duct.
The sperm introduces nuclear material into the egg, which plays an important role in heredity and in transformations in later stages of development, but does not have a significant effect on the early stages. The egg contains everything necessary for full development adult. A mature egg is ready to develop; it only awaits the appropriate stimulus to begin breaking down into cellular units, which constitutes the first step necessary for the development of tissues and organs of a complex adult organism. In many cases, this process can be triggered by physical or chemical stimuli. However, under normal conditions, the onset of the development process is stimulated by the penetration of sperm into the egg.
Questions for self-control
1. What kind of fish sex cells do you know? Describe them. During what process are sex cells formed?
2. What types of nutrition are there for egg cells?
3. What types of eggs do fish have? Classification by size, shape, size.
4. Describe the structure of the fish egg. The structure of the shells. What is a micropyle?
5. What is parthenogenesis?
6. What are the male reproductive cells called? What forms and types do they come in?
BIBLIOGRAPHY
Main
1.Kalajda, M.L. General histology and embryology of fish / M.L. Kalaida, M.V. Nigmetzyanova, S.D. Borisova // - Prospect of Science. Saint Petersburg. - 2011. - 142 p.
2. Kozlov, N.A. General histology / N.A. Kozlov // - St. Petersburg - Moscow - Krasnodar. "Doe." - 2004
3. Konstantinov, V.M. Comparative anatomy of vertebrates / V.M. Konstantinov, S.P. Shatalova // Publisher: "Academy", Moscow. 2005. 304 p.
4. Pavlov, D.A. Morphological variability in the early ontogenesis of teleost fishes / D.A. Pavlov // M.: GEOS, 2007. 262 p.
Additional
1. Afanasyev, Yu.I. Histology / Yu.I. Afanasyev [etc.] // - M.. “Medicine”. 2001
2.Bykov, V.L. Cytology and general histology / V.L. Bykov // - St. Petersburg: “Sotis”. 2000
3.Alexandrovskaya, O.V. Cytology, histology, embryology / O.V. Alexandrovskaya [and others] // - M. 1987
