(B) Gonadal development Fish gonadal development, maturation and spawning processes are strictly cyclical. When the first spawning is achieved, the gonads change regularly according to the regularity of the season, and the cycle does not change. . Barracuda is a fish that reproduces once a year. In order to facilitate comparison and understanding of the maturity of gonad development, artificially divide the gonad development process into several stages. According to the external morphology and internal structure of the gonads, the development of fish gonads is generally divided into six phases. Barracuda is now described as an example as follows: Part I: For juveniles who have not reached sexual maturity. The gonads are transparent and thin lines, close to the dorsal side of the body wall, the naked eye can not distinguish between male and female, the surface can not see blood vessels. The average maturity factor is 0.0937. Seen from the tissue section, the oocytes containing oocytes and juveniles have a diameter of about 0.07-0.09 mm, a large proportion of nuclei, and one nucleoli, usually located in the middle of the nucleus. Phase II: Sexually mature fish that appear in the beginning of development of sexually immature fish or gonadal degeneration. In sexually immature individuals who first reached stage II, the ovaries are flat, red and transparent, and the ovaries are thin. The vascular distribution is clearly visible on the surface. The coefficient is 0.52 and the oocyte diameter is 0.10-0.18mm. After mature egg laying, the ovary returned to the stage II due to degeneration and absorption. It is purple due to vascular congestion. It is opaque. The ovaries have thicker linings, the ovaries have less fullness, appear soft, and a small amount of ovary remains. The 2-4 oocyte transition type of the oocyte. The ovary consists of an oocyte that corresponds to a layer of follicular phase. The cells are round or polygonal. The oldest generation of oocytes have a diameter of 13-179.6 Î¼m, and the nucleus is round, which still accounts for a large proportion. The number of nucleoli increases, about 15-31, ranging in size and distribution along the nuclear membrane. On the outer edge of the oocyte, there is a layer of follicular membrane that is surrounded by a layer of cells, and lipid material appears at the end of the current period. The male testis has a flat, thin band that is 2/3 of its length in the abdominal cavity. Cross cut into sharp triangles with an average maturity of 0.6%. Stage III: The ovary is significantly enlarged. It is cylindrical and pale yellow. The ovary accounts for 2/3-3/4 of the abdominal cavity. The ovum is clearly visible, but the eggs are tightly packed together and difficult to separate. The average maturation factor is 2.369. Vascular traps of the testis of male fish fall into a rosy or pinkish pink, long band, with a length of approximately 3.9% of the abdominal cavity.
Oocytes in the ovary enter the large growth stage. The biggest feature is that the diameter of the oocyte is much larger than the previous stage. It was 170-200Î¼m earlier and expanded to 590Î¼m later. Most of the nucleoli distribute on the edge of the nucleus, and a few are located in the center of the nucleus. The spherical yolk granules begin to form on the edge of the egg and accumulate rapidly. However, the yolk is not completely filled in the entire oocyst, and the oil droplet gradually grows from the periphery of the nuclear membrane. In the entire cytoplasm, the egg membrane thickens, with a two-layered structure of the follicular membrane. Stage IV: The appearance of the ovary is thick and it almost fills the entire body cavity. The ovaries are orange and full of blood vessels. In the early days, the granules could not be separated. The granules in the later period are full and easy to fall off and separated. With slight pressure, the eggs can be extruded. Egg diameter is about 600--800 Î¼m. The average maturity coefficient was 7.436 (4.15--14.7).
The microscopic morphology of the egg is: the yolk granules and oil droplets fill the entire oocyte. According to the changes of oil droplets, yolk granules and nucleus, this phase can be divided into three sub-periods:
In stage IV1 (phase IV) oocytes, the apricot is yellow and the oil droplets are small and scattered between the yolk granules in the ovum. It is not easy to see when microscopically examining live eggs. The nucleus is located in the middle, and the yolk granules increase in size, appearing round or oblong, and are evenly distributed.
In stage IV2 (phase IV) oocytes, the oil droplets became larger and concentrated around the nucleus, and a few oil droplets had begun to synthesize, which was clearly visible on microscopic examination of live eggs. The yolk granules became larger and merged with each other. The nucleus was wavy and the nucleus was toward the animal pole. The nucleolus distributed along the trough.
The oocytes of stage IV3 (end of stage IV) were orange-yellow, and the oil droplets converged into a large oil globules; the yolk granules merged clearly and the nucleus migrated to the end of the animal pole, ie, the so-called â€œpolarization phenomenonâ€ occurred. Cell size tends to be uniform. Male testes are hypertrophied, milky white and 4/5 in length. The cross section is kidney-shaped, and the abdomen can squeeze a small amount of semen. The average maturity coefficient is 8.4%. Phase V: The ovaries pale yellow, soft and inflated, filling the entire abdominal cavity. The egg is transparent and separated. The egg diameter is about 1mm. An oil ball is very clear, mature egg cells released from the follicle, free in the ovarian cavity. When the fish is gently pressed or the fish is lifted, the egg can flow out. The mature egg was isolated from the follicle membrane. There were oocytes in the first and second phases of the ovary and a few oocytes in the fourth stage that did not leave the nest. At this time, the duration was the shortest among the phases. Hours to ten hours. The testis is milky white and fills the entire abdominal cavity. The head of the fish is lifted or the fish's abdomen is lightly tapped. A large amount of semen flows out. The highest maturity factor is 15.0%.
Phase VI: The ovaries that have been spawned for a short period of time or after the spermatorrhea. After licking the eggs, the ovaries shrink, become soft and congested, and appear purple. The ovarian section is in a relaxed state. Due to the expulsion of mature eggs, many gaps are left in the ovary. Some young oocytes can be seen in the section. The oldest phase corresponds to the late phase III and is found in various oocytes. In the gap after ovulation, full of blood, with empty follicles is the main sign of spawning. After the spermatorrhea, the volume of the testis is greatly reduced, yellowish-white, and a small amount of residual semen can be extruded under pressure. The average maturity coefficient is about 3%.
(C) The reproductive season and spawning environment The reproductive season of carps, depending on the species, varies from region to region. At the same time, it is closely related to the habitat. According to reports, the breeding season for American catfish is from December to the end of January. In the vicinity of Qinshan Mountain in Haizhou Bay, China, the spawning period of barracuda is from early May to late. The spawning period in Bohai Bay and Huanghua is from the end of April to early June, and is from the sea between Lianyungang, Jiangsu Province to Rizhao City, Shandong Province, in May. A large number of barracuda eggs can be caught in the upper and middle sifter trawls. The spawning period for the barracudas of Zhejiang Xiangshan Port is from the beginning of April to the beginning of May. The spawning is the highest during the first half of April to the middle of the month (from Qingming to Guyu). Peach blossoms, so fishermen are known as "peach blossoms." Barracudas generally grow in shallow seas. When the spring warmth rises, a large number of broodstock swim to the nearshore shallow water area to feed fat and find its spawning ground. Xiangshan Port in Zhejiang Province is a good place for barracudas to lay eggs. The water depth of the port is relatively transparent (1 to 1.5m). The trend in the port is stable and the waves in the harbor are relatively small. Barracuda is the most concentrated spawning area in the sea area around the Lionâ€™s mouth. There is a wide flat tidal flat. The bottom of the tidal zone is mostly muddy. The bottom is covered with rich yellow-brown â€œoil sludgeâ€ with fresh water flowing into the water. A large number of organic substances and nutrients form a rich area for bait and create good conditions for the bait and young fish. The fish spawning in the harbor was like 6-8m near the reef, and the trend was relatively stable. However, there was talk of water rushing in. The salinity was low (20.7-23.3â€°) and sheltered from the shallows of the inner bay at Xiangwan. . The surface water temperature during spawning is 13-18Â°C and the pH is 8.0-8.2. According to a survey conducted by the Hebei Fisheries Research Institute in the spawning grounds in the Bohai Bay area, the important environmental conditions for the spawning of barracuda are as follows: water depth 1-10m, centered around 6m, muddy or slime, and surface temperature 18-1. At 22Â°C, the salinity is 27.0-30.3 â€°. The pH was 8.04 to 8,30 and the transparency was 0, 27 to 1.0 m. The surface water temperature and salinity were both higher than those in Xiangshan Port. Tide is an ecological factor that causes the spawning of barracudas. The first batch of spawning of barracuda is during the tidal wave (back tide). At this time, the spawning individuals are more concentrated and therefore present a peak. Spawning occurs during the day and night in the sea area. The spawning of P. ostreatus was carried out at 3 to 4 o'clock before dawn. A common group of barracudas chase each other before spawning, and one female fish is often followed by 3 to 4 males (up to 9). Spawning fish groups sometimes lean their abdomen against the mudflats on the bottom of the sea (Yangshan Harbor fishermen use pull-fishing to catch spawning broodstock during the breeding season), sometimes jumping into the water and diving into the water. This kind of intense action is a frictional stimulus. The abdomen and reproductive organs promote sexual maturity and spawning.
(d) Oocyte maturation, ovulation, spawning and overcooking, degeneration and absorption
1. Oocyte maturation In the term artificial reproduction of fish, "mature" has two different concepts: the so-called "fish has matured" means that the oocytes in the ovary have grown large and the yolk is full, reaching the IV level. During the middle and later stages of the period (nuclear polarized to animal poles), stimulation of exogenous hormones can cause normal maturation and ovulation response, so it can be called "growth maturation"; another so-called "egg maturation" refers to the fourth The stage oocyte undergoes the first maturation (decrease) division under the action of an exogenous hormone, releasing the first polar body, freeing the follicular cell from being surrounded, and the egg becoming a free state in the ovarian cavity, within a certain time limit Normally combined with sperm, it is also known as "mature maturation" or "physiological maturation." The former mature biological significance lies in achieving the level of oxytocin production. The latter mature biological significance lies in the ability to fertilize.
2. The ovulation and oviposition of oocytes in the ovary end the stage IV developmental stage into the V stage, the fourth stage of the oocyte outer periphery of the follicle membrane (in this regard due to the physical effect of increasing egg volume, On the other hand, due to the chemical action of the enzyme, the tissue between the follicle membrane and the egg membrane is dissolved and absorbed) and falls into the cavity of the ovary and becomes free. This process is called ovulation. Under suitable environmental conditions, when the broodstock enters the climax, due to the enhancement of sexual activity and the corresponding contraction of the smooth muscle in the ovary, as well as the contraction of the abdominal muscles, the aggregated in the ovarian cavity is completely mature and free. The egg is produced outside the body through the reproductive hole. This process is called spawning. Under normal circumstances, maturation, ovulation and spawning are coordinated with each other. If the ovaries have degenerated, or the eggs are still immature, the temperature of the production water is too high or too low, and the hormone dose is too large, it can lead to maturation. The chaotic step of spawning causes the egg to swell and cause dystocia. The genus Pseudacus is a mature type of ovum.
3. Over-ripening, degeneration, and absorption of eggs (1) The concept of over-ripening: Over-cooking includes both the "overgrowth" of the egg (over-ripening of the ovary) and the "physiological over-ripening" of the egg (over-ripening of the egg). Over-ripening of the ovary: When the ovary develops to the end of the fourth phase, the primary oocyte has grown and matured, and after quitting the dormant state, it waits for conditions to mature and divide. In this waiting time, oxytocin production, ovarian response to oxytocin is the most sensitive, and oxytocin is the most effective, and it is suitable for oxytocin production. If this period is appropriate, the sensitivity of the ovaries to oxytoctics is gradually reduced, and the egg cells begin to degenerate within the ovary and transfer to the stage of being absorbed. At this time, oxytocin rarely has a good effect. If it is too overdone, spawning is still Normal, but the egg membrane is soft, abnormal embryonic development. Over-ripe, but also spawning, but the egg membrane is softer, more deformed, and sometimes the embryo quickly decomposed, leaving only the milky white egg membrane, known as the "hollow egg." When the over-ripening is severe, the eggs cannot be produced. This over-ripening refers to the phenomenon that the gonads are out of date due to the delay of oxytocin production, that is, the so-called "over-ripening of the ovaries" or "overgrowth of the eggs". The over-ripening of eggs means that the eggs that have been discharged from the follicles lose their ability to be fertilized because they are not produced in time outside the body. The secondary oocyte that is in the middle of the second maturation split can receive sperm for a period of up to several hours, but the optimal time is only about 2 hours. Outside this optimum time, the embryo is barely fertilized. Most of the development is deformed or even disintegrated. If it is further from this period, it cannot be fertilized. Therefore, the proper maturation time of the egg within 2 hours after the middle metaphase is when the egg can be called "mature egg", and not called "immature egg" at this time. If it exceeds this time, it is Cooked eggs."
(2) Degradation and Absorption of Overcooked Eggs: After spawning of females, a large number of ruptured follicles, oogonia, primary oocytes, and some unfamiliar, oversized secondary oocytes are left behind by the ovaries. . All of these, except oocyte, have been degraded and absorbed. Absorption of non-discharged overcooked eggs mainly depends on the function of follicular epithelial cells and absorption of young oocytes. Since the follicular membrane in the periphery of these oocytes has not yet formed, they are in some macrophages. Phagocytosis is absorbed, and the ruptured follicles after ovulation gradually expand into spongy in the ovary. Soon after its composition has undergone sexual changes and decomposition, the decomposed substance is absorbed into the blood. As the degenerated eggs are absorbed, the ovaries gradually contract. At the end of the absorption, the gonads return to phase II.
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