Teach you to master the techniques of river crab culture on the big water surface from five aspects.

Crab, also known as hairy crab, crab, scientific name of Chinese mitten crab, often inhabits in fresh water, rich in aquatic waters, with the characteristics of daytime and nighttime, generally come out to feed at night. June to September of each year is the peak period of crab feeding activity. Large water surface culture crab has the advantages of smooth water flow, large wind surface, sufficient dissolved oxygen and abundant natural food. Therefore, using large water surface culture crab can significantly reduce production costs and improve culture benefits. Now combined with my town for many years breeding experience, its technical points are summarized as follows.

1 Preparation before stocking 1.1 Selection of waters According to the biological characteristics of river crab, fresh water quality, sufficient sunshine, abundant aquatic plants (preferably bitter grass, verticillata, etc. in submerged plants, reed and cattail grass in emergent plants) and waters with more snail clams (insufficient snail clams can be artificially bred) should be selected. In this way, the crab can obtain sufficient animal and plant bait, which is conducive to meeting and promoting the growth of the crab. Where there are not many aquatic plants, artificial planting of some aquatic plants can be adopted to make up for it. 1.2 Establishment of escape prevention facilities Fence the aquaculture waters with netting and stumps (bamboo stakes). Block appropriate polyethylene mesh, mesh size to avoid crab is appropriate, it is best to use double-layer purse seine. The height of the blocking net should be 1 meter above the annual average water level. The legs of the net are sunk into the bottom mud with stone cages, and the net is inserted into the soil with barbed piles. The inner layer of the net is made of plastic film or calcium plastic plate to prevent the crab from jumping out of the net. Tree (bamboo) piles are inserted into the soil 0.5 - 1.0 meters at certain intervals to strengthen the net and prevent wind and wave impact. 1.3 Desolator Before stocking juvenile crabs, we should adopt various methods to eliminate wild fish in the waters in advance, reduce the natural enemies of crab, and provide a suitable breeding environment for crab. 2 crab breeding 2.1 Strictly control the quality of crab species Breeding benefit is good or bad, seed is very important, when buying seed should pay attention to the following points. 2.1.1 The young crabs (crab species) purchased should be neat, healthy, disease-free and injury-free, which is the first and most basic condition. 2.1.2 In Jianghuai area and Yangtze River valley, Yangtze crab is the first crab species to be purchased, and its growth rate and recapture rate are better than other crab species. Under the same conditions, the sexual maturity of Liao River crab is earlier than that of Yangtze River crab, and the average size of individual is naturally much smaller. 2.1.3 Crab breeds cultivated in inland pure fresh water are better than those cultivated in coastal areas. Generally speaking, the cultivation water in coastal areas has a certain salinity, and the crab seedlings cultivated are not adapted to inland waters, easy to mature, and the growth rate is not ideal. Therefore, if conditions permit, it is best to cultivate young crabs by themselves. 2.1.4 From the results of many years of cultivation, ecological soil pond seedlings are better than factory cement pond seedlings, and the seedlings cultivated in the former are more suitable for natural stocking, especially large water surface stocking. 2.2 Establish stocking time in time Large water stocking should be winter and spring-based, December of each year and March of the following year-April is the best stocking season, cold winter and freezing generally should not be stocked, so as not to frostbite crab species, affecting the survival rate. 2.3 Determine reasonable stocking quantity The stocking amount should be determined according to the natural bait in the waters and their own economic strength. The crab species were stocked at a density of 400 - 600/667 square meters at 200 - 300/kg. If the area is large, the bait is sufficient, the water quality is good, and the funds are guaranteed, the dosage can also be appropriately increased, but it cannot exceed the natural bait supply capacity of the water area. 2.4 Adopt scientific stocking method Before stocking, load the crab seeds on the boat, put them as evenly as possible, and enlarge the range. If it is a crab species purchased from other places, due to long-distance transportation and long dehydration time, it is not suitable for direct placement, but the young crabs should be treated first, that is, soaked in water together with the net bag for 1 - 2 minutes, removed and placed for 3 - 5 minutes, so repeated 2 - 3 times, until the young crabs fully absorb water, adapt to the water environment and then stock according to the above method. 3 Feeding management 3.1 bait feeding Large waters are generally rich in aquatic plants, generally do not need to feed in the early stage, July-September is the vigorous growth period of river crabs, in order to effectively protect the aquatic plants from a large number of damage, at this time should be timely feeding part of the artificial bait, such as snails, river clams, fish and shrimp meat, etc., plant bait in the grain, beans, pumpkin silk, potato silk, etc., in order to better promote the rapid growth of river crabs. Generally fed twice a day, 8 - 9 am and 17 - 18 pm each feeding 1 time, daily feeding amount should be 5%-7% of crab weight. In the morning, it should be fed in the deep water area of aquatic plants, and in the afternoon, it should be fed in the shallow water area of aquatic plants. 3.2 water quality management Large water bodies are generally unblocked, and the water quality is not easy to deteriorate. However, when the aquatic plants are bitten off by crabs floating on the water surface, they should be taken out in time to avoid decay and deterioration of water quality in high temperature seasons. Organophosphorus and pyrethroids are prohibited from polluting water quality. In addition, every 15 days with quicklime according to 25 - 30 kg/667 square meters of water poured into the whole pool to improve water quality. 3.3 daily management First of all, it is necessary to strengthen the management of blocking nets and check whether there are loopholes in the fence in time. If loopholes are found, they should be repaired in time, especially in flood season, when crabs are easy to escape with the flow of water. In addition, it is forbidden to fish aquatic plants, put ducks and fish underwater during the growth period of river crabs, because it is easy to cause river crabs casualties, especially during the peak period of river crab molting, which is more harmful. 4 Disease control 4.1 pond cleansing and disinfection should be carried out as far as possible. 4.2 Operation process action should be light, fast, try not to make crab body injury. 4.3 To reduce the occurrence of diseases as much as possible, the combination of sprinkling quicklime regularly and feeding oral medicine with bait was adopted. Commonly used drugs are norfloxacin, heparin, FRC and so on. 5 adult crab fishing The culture of river crab in large water surface is different from that in pond, so it should be caught in due time. Since the middle of September, a considerable number of river crabs attempt to escape from the net enclosure, so it is important to determine the fishing time in time to improve the recapture rate and reduce the escape of river crabs. Therefore, large water surface blocking net cultivation crab, must be caught in advance, generally choose in early September, catch in time for adult crab natural reproduction migration before the concentration of efforts to organize fishing, usually land cage and crab (Ecstasy array) fixed catch, fishing effect is better.