The crabs used for the early spring nursery production of Chinese mitten crab (Crab) are usually mated in the late autumn or early winter of the previous year. Raising the egg holding rate and the survival rate of overwintering and gaining the quality and quantity of the brooding crabs are the basis for the smooth progress of the entire nursery production. The overwintering cultivation of the crabs should be grasped as an important management task. I. Overwintering pool selection: Pro-crabs are generally wintered in outdoor soil pools. Overwintering ponds have been chosen where they are sheltered from the wind, near the water, and where the environment is relatively quiet. East to west rectangular or square pool, water depth of 1.5m or more. The best soil is clay or clay. In front of the pool, the pro-crab person first clears the pool and removes mud from the bottom of the pool. The bottom of the pond is plowed and dried for more than 10 days. Disinfection generally uses quicklime (75-100kg per acre) or bleaching powder (7-8kg per acre) to be splashed in the whole pool, and water is injected after 7 days. Second, the pro-crab choice and mating spawning: the choice of pro-crab, first, to ensure the purity of germplasm, it is best to collect wild green crabs from rivers, lakes and other natural waters, according to 2:1 or 3:1 female Male and female proportions. The second is to select individuals who have complete limbs, clean, hard shells, good fatness, strong vitality, and consistent specifications. In order to enhance the consanguinity of the crabs, 10 to 15 days ahead of time, female crabs should be placed in freshwater holding pools for intensive cultivation. When the water temperature is between l0°C and -15°C, sea water is added to gradually increase the salinity of the pool water to about 25‰, and the male crabs are put into spawning and mating. After 5-7 days, remove the male crab and allow the female crab to overwinter in the outdoor earth pond. Stocking density is generally controlled within m23. Third, the bait feed: Choose rich live fresh bait, such as sand, fresh fish and so on. Before mating, micro-overage feeding, daily feeding amount is generally 8% to 12% of the total weight of pro-crab; after conserving eggs, as the water temperature continues to change, depending on food intake, daily feeding amount is generally controlled in the pro-crab 2% to 10% of total body weight. Regardless of how the surface water temperature changes, as long as it is found that the pro-crab activists, it is necessary to feed properly. Feed it once a day before sunset and put it below the water level along the pool. In the second day, the patrol pool checks the feeding situation, removes the residual bait, and adjusts the amount of feeding. To feed more than one type of bait alternately. Water quality regulation: During the winter, the key is to maintain the relative stability of the water environment. The main water quality indicators are measured in ten days, with a salinity of around 25‰, dissolved oxygen of over 5mg/L, pH value of 7.8--8.7, and leaking pools. Water is added once every five to seven days to keep the water level above 1.5m, and it is not necessary to change the water. If water needs to be changed, the amount of water changed every time does not exceed 30% of the total water body. When you freeze, insert a proper amount of straw. Before the sun rises in the morning, it is necessary to break the ice and clean the snow on the ice. V. Daily Observations: Each morning and evening, each inspecting the pond once to observe the activities of the crabs, feeding conditions, changes in water color, etc.; check whether the anti-escape facilities are damaged; regular inspection of the development of fertilized eggs every ten days, timely adoption and adjustment Management measures to ensure the pro-crab overwintering.
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