The artificial propagation of freshwater pelicans mainly depends on the development of gonads, and the whole process of gonadal development has a certain regularity. This regularity is revealed through the special morphological structure and physiological characteristics of the gonad development at various stages. It is under the control of the nerve-integrated liquid. These are the internal rules of their reproduction, and they are also the root causes that affect the breeding of freshwater whitefish. Artificial breeding of freshwater pelicans is to provide reliable theoretical basis and technical measures according to this law. Since the introduction of freshwater whitefish into the mainland of China in 1985, many scholars and production units have conducted detailed studies on their gonad development and spawning types, and conducted large-scale experiments on artificial reproduction of freshwater whitefish, and achieved promising results. . This chapter is based on the results of domestic research and is based on foreign research. Freshwater white pelicans gonadal development pattern female pair of freshwater white fleas ovary, symmetrically located on both sides of the iliac crest, before the second milky white lines, surrounded by large fat body, difficult to distinguish. The histological features of oocytes at different phases (1) Phase I oocytes: Phase I oocytes are separated from the oocyte and are distributed in the stromal matrix. The cells are small, round or oval in shape, and the cytoplasm is pale purple with a diameter of 14.35-26.57 μm. The nucleus is 1/2-2/3 of the cell area and the nuclear diameter is 7.45-16.79 μm. The chromatin in the nucleus is filamentous. Sparse nets are formed, and there are 1 to 4 darkly colored small nucleolus on the median plane. The ovary mainly composed of the first phase oocytes is called the first stage ovary. (2) Phase II oocytes: The volume of the oocytes was larger than that of the first phase. During oocyte development, the egg diameter increased from 21.3 μm to 255.3 μm, the nuclear diameter increased from 15.96 μm to 106.4 μm, and the chromosomes in the nucleus gradually disintegrated. However, filamentous remnants are still visible, and the number of core nucleolus is increased. There are 11 to 27 sizes of nucleoli on the median cut surface, which are generally located inside the nuclear membrane. The cytoplasm is strongly basophilic and is stained dark purple by RE (Helimat Hematoxylin-Eosin), with connective tissue and blood vessels distributed between oocytes. In the oocytes of the early phase II, a dark blue colored lumpy nucleus is seen; in the phase II, there is a thin layer of follicular cells outside the late oocytes, and the nucleus is not easy to find. There is a transparent layer around the nucleus, which is separated from the cytoplasm by the protoplasmic membrane. At this time, the cytoplasm staining is shallower than the early stage, the cell diameter and the nuclear diameter increase relatively, and the yolk nucleus disappears. At the later stage of phase II, nucleoli material began to enter the cytoplasm, and a considerable part of the nuclear membrane was incomplete, with local dissolution, rupture, and perforation. The ovary, which is mainly composed of primary oocytes at phase II, is a stage II ovary. (3) Phase III oocytes: The volume of cells increases, the thickness of the egg membrane increases, and there are two layers of follicular cells outside the cell. The outer cell nucleus is flat and long, the inner nucleus is elliptical, and the cell boundary is not obvious or absent. During the development of phase III oocytes, the egg diameter increased from 273.7 μm to 422.1 μm, the nuclei became large and round, and the nuclear diameter increased from 95.7 μm to 242.0 μm. On the median cut surface, 25 to 49 sizes can be seen. Nucleolus. At the time of the third phase, there were also nucleolar efflux phenomenon in the early oocytes; blue-violet particles appeared in the cytoplasm and gradually increased. A layer of vacuoles of varying sizes appears near the egg membrane, and then grows with the oocyte. The number increases from one layer to several layers, and is distributed unevenly in the vacuole. Yolk vesicles are generally considered to be a kind of mucopolysaccharides. III cells in the late phase are filled with blue particles; at the same time, some of the yolk granules that have been stained with RE by the RE appear in the cytoplasm near the nuclear membrane. For the yolk globules, the yolk gradually increases (filling the whole egg cells up to the V phase); a layer of light outside the egg membrane that is stained with RE for light red is called a radiation zone. Most of the nucleolus are located at the nuclear edge, and a few are scattered at the core. The ovary, which is mainly composed of primary oocytes at the third phase, is stage III ovary. (4) Phase IV oocytes: The yolk fills the extranuclear space and contains only a thin layer of cytoplasm around the nucleus and at the inner edge of the egg membrane. Egg diameter increases, follicular cells are not clear, egg membrane thickening. The early nucleus is irregularly oval and is distributed in the center of the oocyte. Afterwards, the nuclear phantom gradually becomes uneven and wave-shaped, so as to increase the contact surface between nucleoplasm and cytoplasm. At this time, the nucleolus are mostly distributed on the edge of the nuclear membrane, and a few are in the central core. This period can be based on the cell size and the nuclear position in three periods: In the early stage, the egg diameter increased from 421.1μm to 473.3μm. There is still a weakly alkaline cytoplasm around the nucleus. There are also some vacuoles in the cytoplasm. The nucleus is located in the center of the cell, with a nuclear diameter of 178.9-273.8μm. The nuclear membrane is corrugated. There are 0-68 nucleoli on one aspect and the radiation layer is thickened. Mid-term: egg diameter reaches 94.7-684.2 μm, yolk granules are filled with cytoplasm, and a few particles form lumps. The nucleus is still in the center or slightly shifted, with a nuclear diameter of 117.0 to 284.2 μm. The nuclear membrane is obviously corrugated. At the mid-cut plane, there are more than 100 nuclei with a blue granular substance inside. Late stage: The oocyte is basically mature with an egg diameter of 663.2 to 1084.2 μm. The yolk granules form a mass with a nuclear diameter of 231.6 to 315.8 μm. The nuclear membrane is still corrugated. The nucleolus gradually disappears and the nucleus gradually shifts to the side. The polarization of the earth, the non-disappearing nucleolus are mostly concentrated in the nuclear region of the animal pole, and the entire oocyte polarity is completed. At the same time, a funnel-shaped depression can be seen on the extreme section of the animal called the clear hole, which is formed by the radiation band, the egg membrane and the filter membrane together. At this point the primary oocytes have grown to their full body and reached the mature phase IV. The ovary dominated by the primary oocytes of this phase is called the stage IV ovary. The growth period during egg development is relatively long. When the primary oocyte reaches the maximum volume during development, the volume of the oocyte is increased by tens or even hundreds of times. (5) V-phase oocytes: The nucleus has moved to the vicinity of the animal pole, close to the fertilization hole, and the nuclear membrane disappears. Only a group of nucleoplasms can be seen. Concentrated chromatin can sometimes be seen, and maturation changes. Therefore, it is also called the mature period. In this process two mature divisions occur, namely meiosis and equal division. In this process two mature divisions occur, namely meiosis and equal division. Under suitable physiological and ecological conditions, the flowing eggs are produced from the ovary and are called spawning. The maturation period proceeds quickly and can be completed in hours or tens of hours. The mature and flowing incubator is called the V-phase secondary oocyte. At this time, the ovary is in stage V. Sexual mature freshwater pelicans, in good physiological and ecological conditions, the ovary transition from phase IV to phase V, after the completion of spawning, it becomes the ovary of stage VI. If the oocytes of phases III and IV are not further developed and mature until ovulation, or the egg matures and misses the proper season of egg production, the oocyte will degenerate and be absorbed. In the process of degeneration and absorption of oocytes, mainly due to the secretion of follicular epithelial cells, the membrane ruptures and dissolves, followed by the fusion of nuclear and cytoplasm, while the follicular epithelial cells engulf yolk, peripheral connective tissue and lymphocytes. It is also involved in phagocytosis and is transferred back to the mother for nutrition. The entire absorption process lasts for a long time. At the same time as the oocytes begin to degenerate and absorb, the new generation of sexual cells begin to grow again. At the end of the absorption, the ovaries return to phase II. Testis stage I: thin, transparent, close to the body wall, the naked eye can not distinguish between male and female. At this time, seminal vesicles and seminiferous tubules have not yet formed. The primordial germ cells undergo cell division and form spermatogonia, which do not show a fixed arrangement. The volume is relatively large. The diameter is about 16 μm, and the proportion of nuclei is large, about 9 μm. Phase II: Fine band, translucent or opaque, blood vessels are insignificant, width of about 2 to 4 mm. Seminal vesicle formation, spermatogonia increased, arranged in bundles, this is a solid ampulla stage, the ampulla between connective tissue separation. Phase III: Generally, the thickness of chopsticks is pink, yellow or white, and the surface is flexible and the blood vessels are obvious. The lumen of the center of the ampulla is solid, and the ampulla wall is lined with a bundle of sperm vesicles consisting of layers of primary spermatocytes and surrounded by seminal vesicle cells. Phase IV: Large female fingers are thick, milky, wrinkled on the surface, and are about 2 cm wide. The ampulla of the ampulla of the ampulla consists of a group of primary spermatocytes, secondary spermatocytes, and spermatids, showing active differentiation and division, easily distinguishable from other stages, and some cysts also have a few spermatozoa, but Not dominant. Phase V: The testis is plump, milky, and has reached full maturity. Uneven surface, wrinkles deepen. There is a lot of creamy white semen out of the abdomen. Each ampulla is filled with sperm. In addition, there are sperm cells and cells that have metamorphosed into the sperm, and there are also a small number of cells in each early stage. Phase VI: Testis after spermatorrhea, fine banded, pinkish or pink, testis withered, and no semen could be squeezed. The sperm sac wall has only connective tissue and a small amount of primary spermatocytes and spermatogonia, and there are residual spermatozoa in the cyst and ampulla. The composition of oocytes in different growth stages of ovary and the stage of freshwater white fleas belong to the introduction of Dalo tropical fish species. Its living temperature range is 12～35°C, the suitable growth temperature is 21～32°C, and the optimum breeding temperature is 25～28°C. Natural breeding populations cannot be formed in the natural waters of China University of Defense. The breeding and breeding of broodstock must be carried out at wintering sites such as hot springs. (b) Broodstock breeding techniques Broiler breeding is a very important part of artificial breeding of freshwater whitefish. The quality of broodstock cultivation has a direct impact on the maturity of the gonads, the productivity of the gonads, the fertilization rate and the hatching rate of the eggs, and therefore must be taken seriously. Sources and selection of broodstock (1) The source of broodstock is mainly cultured in ponds after introduction of freshwater whitefish. It is difficult to form natural populations in rivers, lakes, and reservoirs. Therefore, the source of broodstock is mainly derived from the pond to reach broodstock of mature age, or Purchased from other units. However, when choosing, individuals with large body size and fast growth should be selected as broodstock, and fish with close relatives should be avoided as broodstock to prevent degradation of future generations and affect growth. (2) Selection of broodstock 1 Identification of males and females: When broodstock breeding and aphrodisiac spawning, it is necessary to grasp the appropriate proportion of males and females, and it is necessary to correctly identify male and female broodstock. Freshwater daylight has not yet seen obvious secondary sexual characteristics until the breeding season is not easy to distinguish between male and female. The selected broodstock must be a bred broodstock with strong physique, smooth surface, and no scars. Freshwater whitefish can not be identified from the pectoral fin touch, the general characteristics of the female is: prenatal selection, the female abdomen enlargement and loose, can show the outline of the ovary, the reddish hole slightly open slightly, with digging Visible eggs visible; male fish is characterized by: male body hernia from the anterior chest to the abdomen shows red, deeper and more vivid than the female, the body was silver-gray, cloacal closed slightly, squeeze the peritoneal fluid with semen . 2 Mature age and body weight, age and weight are all positively related in normal circumstances, that is, the greater the age, the greater the body weight; otherwise, it is small. In different cultivation processes, due to different ecological conditions and nutritional conditions, the differences in body weight are quite different. For broodstock breeding, the mature age is generally 3 years old. According to Linsenjin and De Paiva et al., the first sexual maturity of freshwater whitefish is 2 years and 9 months. The general choice of weight is: females 2 to 5 kilograms, males 2 to 3 kilograms is appropriate. The conditions for breeding broodstock and the selection of broodstock cultivating should be based on the actual situation, and should be adapted to local conditions and to ponds with poor environment. (1) The conditions of the broodstock culture pond The location of the broodstock pool is close to the water source, and the injection and drainage are convenient, and the water quality can be adjusted. An area of ​​3 ~ 4 acres, water depth of about 1.5 meters, with a good rectangle, easy feeding and management and fishing. The bottom of the pool is flat and free from obstructions. There is proper mud in the bottom of the tank, but it is better not to exceed 20 cm. If the number of broodstock is small, it can be mixed with tilapia, broodstock, and other broodstock, but it should not be mixed with squid, otherwise it will affect gonad development. The gonad development water temperature requirement is 21 ~ 32 °C. (2) The method of clearing the broodstock pond in the broodstock culture pool is the same as that of the seedling pond. However, the pro-fish pond does not have any leisure time. Once the broodstock has been used up for each pool of broodstock, it is necessary to seize the time to clear the pond so that the broodstock can be stocked. The contents of the clean-up work include excavation of excess silt at the bottom of the pond, maintenance of ponds, removal of weeds, and removal of wild fish. Cultivation of freshwater white brood broodstock (1) Stocking densities and a reasonable stocking density between male and female are important conditions for ensuring the success of broodstock breeding. The stocking density of broodstock can not only fully utilize water but also make gonads develop well. Freshwater whitefish is better as a single culture, otherwise, a variety of fish will affect their gonadal development due to intensive cultivation. The stocking weight per acre is 100-150 kg, the maximum is about 200 kg, the number of rearing rearing tails is 30-50, and the tail weight is 3-5 kg. Due to the small number of broodstock in some units and the small scale of reproduction, freshwater white bream broodstock can be mixed with the broodstock of China's four populations, but this method is not conducive to intensive cultivation. The proportion of males and females that stock broodstock is mainly related to the mode of reproduction, that is, the method of insemination. If artificial insemination is used, the proportion of males and females should be 1:1. If natural fertilization is used, the ratio of males to females is preferably 1:1.5. Otherwise, it will affect the smooth progress of production. (2) Cultivation method 1 Conventional cultivation: If only one egg is prepared for production in one year, routine cultivation can be adopted, and the principle of “concentrated feed, green feed combined with feeding, supplemented with appropriate application of manure, regular flushingâ€. The concentrates mainly include conventional concentrates such as bean cakes, peanut cakes, barley, wheat, malt, alfalfa, bran, silkworm cocoons, etc. The green material can be selected from cabbage leaves, watermelon rind, water grass, or dry grass. Manure is produced from cow dung, pig dung, or human waste, and fertility is increased, and organic debris is increased. However, the use of chemical fertilizers is not effective. Since freshwater whitefish should live in water with higher water temperatures throughout the year and even in winter, they should maintain a strong feeding rhythm. Therefore, it is necessary to ensure uninterrupted feeding throughout the year. Fertilization: The application rate of basal fertilizer is generally 300-400 kg per mu. The principle of applying topdressing is to “apply less, apply frequently, and look at water and fertilize.†However, the fertility should be lower than that of the pond. According to pond fat, season, weather and water temperature and other flexible conditions. And often add new water. The number of water additions during ripening should be increased, preferably 1 to 2 hours. Feeding: Because freshwater white plage is a feeding fish, it is difficult to satisfy the need for gonad development by fertilization alone. The amount of concentrate feed usually accounts for 3 to 5% of the broiler's body weight. If the water temperature is low and the feeding is weakened, feeding should be reduced; if the water temperature is high, the feeding amount should be increased particularly in summer and autumn. The broodstock is restored to its constitutional stage after spawning, and the quality of the concentrate feed is better. Feed 1 to 2 times a day, usually 9 to 10 in the morning and 3 to 4 in the afternoon. Concentrates can be placed at a fixed point in the pool and there is no need to use a food table. The number and frequency of feeding of green feeds are indeterminate, and feed intake is generally interrupted depending on the feeding conditions of fish to supplement the deficiency of certain trace elements and vitamins. It is important to pay attention to routine cultivation. Postpartum uses mainly fine and green materials, and less manure is applied. Appropriate manure is applied in autumn and winter and spring to keep the water body at a certain degree of fat, and it is fed with concentrate; about a month before birth Increase high protein feeds, such as bean cakes, cocoons, etc. to accelerate gonadal development, and pay attention to flushing. Freshwater white brood broodstock can be spawned with intensive education. 2 Intensive cultivation: If multiple spawning trials are conducted during the year, intensive cultivation should be carried out. According to reports, after freshwater white plover spawns in the spring, after 50 days of intensive cultivation, it can revive production and lay eggs successfully. General production units adopt intensive cultivation. The intensive cultivation is mainly based on pellet feed, supplemented with a small amount of green material, and often flushed to achieve the goal of rapid development of gonads. The protein content of pellet feed is generally between 25 and 33%, and the highest is 35%. It is fed twice a day, at 9 to 10 o'clock in the morning and at 3 to 4 o'clock in the afternoon, and the feeding amount accounts for 3 to 5% of the fish's weight. The high temperature season is 5 ~ 7%, and appropriate feeding green feed, generally do not apply organic fertilizer during the cultivation process; at home more than 0 days of intensive cultivation process, should be flushed regularly, the early general every 5 ~ 7% days flush once , Flush every 1 to 2 days later, each time 2 to 3 hours. The stimulation of running water makes the broodstock develop further in the late stage of development (phase IV) and improve the aphrodisiac effect. Because of the water flow measures, the gonads have entered the end of the fourth period, especially before the aphrodisiac, and the effect is very good. In the broodstock breeding process, the formulation of pellet feed can refer to the recipes of Zhang Zhongying et al. (1991) and Ma Zhongbo et al. (1988): A: fish 10%, soybean cake 25%, rice bran 10%, bran 10%, mixture (for pigs, Contains about 13% of crude protein) 18%, mixed salt of calcium phosphate 2%, plus a small amount of microsatellite mixture. Crude protein was 29%. Can also refer to the formula of squid, according to local conditions, appropriate selection of local raw materials for preparation. Whether it is a conventional cultivation or an intensive cultivation, the combination of artificial ripening and ripening can be better at the same time. Freshwater whitefish is a tropical fish, it is difficult to naturally overwinter in most areas of China, even in Guangdong should also move to winter in the greenhouse. Therefore, it is also very important to cultivate broodstock in winter.