New technology of artificial culture of river crab with fresh water

River crab, commonly known as crab, also known as hairy crab, mitten crab and so on. Belongs to crustacean, square crab family. The head and chest are square and round, usually 6-7 cm long, usually green. The chelate foot is strong, densely tomentose, and the side of the foot is flat and long. Wild river crabs live in the banks and mudflats of rivers and lakes, and are produced all over the north and south coastal areas of our country. Because of its unique fresh water growth, reproduction and migration in the sea, it provides natural conditions for artificial breeding. The methods of artificial culture are briefly introduced as follows:

1 to build the land. Crab culture ponds should be built in places with good water quality, sufficient water sources, convenient drainage and irrigation, and plenty of sunshine. The excavated terrain should be neat, and the east-west rectangle is the best. The pool is 1.5 meters deep and the water depth is 0.8 meters. Because the river crab has a strong climbing ability. And make holes to escape. Therefore, the fence should be started at 20cm to 30cm below the bottom of the pool, with a height of 150cm to 180cm. Above the use of brick or cement board for eaves, to be factory-shaped, eaves width of 15 cm to prevent river crabs from climbing and escaping. The wall should be smooth with cement, and the entrance and exit should be strictly protected from escape with aluminum wire fence. At the bottom of the pond, soil is also used to make long ridges of hills, and water plants such as Zizania caduciflora and water peanuts are planted on the edge of the trench to inhabit the river crab camp. The coverage of aquatic plants should reach about 70%. If it is not recommended, you can pick up some aquatic plants and put them on the edge of the pool. It can also play the same role as planting aquatic plants.

2transporting seedlings. According to the characteristics that river crabs spawn and reproduce in the sea and grow and develop in fresh water, artificial breeding must transport seedlings over a long distance. At present, although artificial breeding of crab seedlings has made a major breakthrough, it is still limited to key research units, which can not meet the needs of extensive breeding around the country. The Yangtze River Port in China is a natural breeding ground for crab fry. More than 20 provinces and cities across the country buy crab fry from there and transport them back for breeding. But the method of transporting crab seedlings must be done in order to improve the survival rate. Jiangsu Aquatic Technology Promotion Station, after repeated research and experiments, finally successfully studied the method of oxygen-filled water transport of crab seedlings in double-layer plastic bags. That is, the double-layer plastic bags are filled with 3-5 kg of water, the salinity is controlled at about 4%, and then each bag is filled with 100-150 grams of crab seedlings, and then filled with oxygen, the volume of oxygen is 10-12 liters. Finally, tie the mouth of the inner and outer plastic bags tightly, put them into cardboard boxes and take them away. Each person can take 10 bags at a time, that is, 1500 grams, transport 400km, and walk for 8 to 13 days. The survival rate can still reach 80%, and the high rate can reach 95%. It is an economical and effective method for transporting crab seedlings.

3stocking. 40 days before the purchase of crab seedlings. To use quicklime plus bleach to disinfect the breeding pond, generally 10 kg of quicklime and 0.5 kg of bleach per 0.1 mu are scattered into the water in the pond (usually 3-6 cm deep) and stirred repeatedly to completely eliminate pests and enemies in the water. Then put all the water away, rinse again with clean water, and continue to disinfect with sunlight exposure. Fresh water can be poured 15-20 days before seedling release. Generally, you can go out to buy seedlings in May to June. The newly transported crab seedlings can not be put into the pond immediately, but should be put in the breeding pond or temporary culture pond with plastic bags for half an hour. When the internal and external temperature is close, open the plastic bags and pour the crab seedlings into the pond. Usually, 5-100000 animals can be stocked per 0.1mu, which needs 30000g. The water quality and feed conditions are good, and the density can be appropriately higher. When throwing crab seedlings, the pool water should be a little shallow, about 0.5 meters deep, in order to increase the water temperature. Reduce death and promote growth. After a week of feeding, the water level was raised day by day until the depth reached 0.8 meters. For the young crabs raised for one year, 800 crabs can be put in every 0.1 mu, which can be released from April to May.

(4) feeding. River crab has miscellaneous feeding habits and a wide range of feed, mainly animal and plant feed. Animal feed is mainly ground into paste small miscellaneous fish, snail, fish offal, livestock and poultry blood, earthworms, fish meal and so on; plant feed is mainly soybean meal, corn meal, wheat flour, wheat bran, rice bran and so on. Generally, half of animal and plant feed is better, and a small amount of green feed such as water and grass should be mixed and fed. The feed for the first release of crab fry is mainly fed with fish and shrimp paste. Usually, the feeding should adhere to the principles of four looks (depending on the season, weather, water color, and feeding activities of river crabs) and four determinations (positioning, quantitative, timing, qualitative). The time is 8-10:00 and 3: 5 p.m. The dosage is generally based on the fact that the feed dropped each time can be eaten up within two hours. The amount of feeding should gradually increase with the growth of river crabs, generally 0.5 kg per 10 kg of river crabs per day. The aquatic plants in the pond can not only be used as fodder, but also shade and prevent heat, which is indispensable for raising river crabs.

5Management. River crabs like to live in fresh water and water plants, and are particularly sensitive to hypoxia, so the breeding pond must often be injected with new water. The water is changed every 10-15 days in the early stage, and every 2-3 days in the hot summer and autumn season. The amount of water for each change is 2 percentile 3 of the pool water. The smelly pond mud should be removed by stages. If the pool water is too fat, you can grow some aquatic plants such as water peanuts by the pool. In this way, it can make the river crabs molt in the water and avoid killing each other. At the same time, aquatic plants can also absorb nutrients in the pond, increase the amount of dissolved oxygen in water, prevent the deterioration of water quality and benefit the growth of river crabs. There are also many enemies of river crabs, so it is necessary to strengthen prevention and control work. Its main enemies are rats, water snakes, water birds, frogs and water centipedes. It is reported that a mouse is the most ferocious enemy that eats or kills 10 river crabs a day. A variety of effective methods should be adopted to kill and prevent rodents. When water snakes, water birds, frogs and water centipedes are found, they should be beaten and driven away in time to ensure the normal growth of river crabs.