Techniques of ecological culture of hairy crabs in river ditches

Gully selection

Crab culture ditch requires fresh water quality, no pollution in the upstream, flat bottom, not too thick silt, transparency 30~40cm, dissolved oxygen not lower than 5mg/L, perennial water depth of 1.0 ~ 2.5m, small water level drop and slow flow. River ditch lush water plants, mainly verticillium verticillata, bitter grass, Malay herb-based, there are a small number of grass, water peanuts and so on. The transportation is convenient for management and transportation.

Block design and installation

Safe and reliable anti-escape facilities should be established for crab culture in river ditches, and the strength of the equipment must be commensurate with the highest water level and maximum flow velocity of the river. The structure of the block is composed of a wall net, a support and a stone cage. The wall net is the main part, which is generally woven with 0.21 × 3 × 4 polyethylene thread, the mesh size is about 1.5cm, and the upper and lower parts are equipped with double-wire rope with diameter 5mm. The height of the wall net is 4.0m and 4.5m. It is equipped with a double-layer net to prevent escape and pollution in the outer network to prevent the invasion of wild miscellaneous fish. The interval between the internal and external network is 2mm 3m, during which a capsule net is installed, which can be used to check whether there are crab seedlings fleeing or wild miscellaneous fish entering, in order to judge whether the block is broken. The stone cage is a facility for fixing the bottom class of the wall mesh, which is stitched into a cylindrical mesh bag of diameter 15cm with a mesh made of 3 × 4 polyethylene (mesh 2~3cm) with a diameter of 3~4cm in it. When getting off the net, it is stitched with the wall net along the bottom class and pressed into the sediment 35cm. The top of the wall net is sewn with a wide 40cm plastic film on the inside of the screen to prevent the crabs from climbing and escaping. Insert bamboo or wood piles with a straight diameter of 12cm and a height of 4cm every 2m, insert them into the bottom of the pool at 0.5m and 1.0m, connect them into a whole with a crossbar, tie the wall net to the pile and fix the net shape.

Preparation before sowing

1, clear the field to eliminate pests: in general, there are some wild snakehead, catfish, carp and other enemy fish in the river ditch, which must be completely removed, otherwise it will affect the habitat and feeding of river crabs. In particular, the river crab has just molted, its body is soft and its mobility is poor, so it is easy to be eaten by these enemies and reduce the recapture rate. Electric capture, net capture, etc., can be cleaned up step by step from one end, and can also be cleaned up with drugs from the upstream.

2. Crab species selection: it is better to use the natural or artificial crabs cultivated in the Yangtze River system, and the crabs can be bred by themselves to reduce the cost. Require neat specifications, strong physique, complete appendages, active crawling, no disease injuries and attachments, sexually mature old crabs should be removed. The crabs purchased in the same batch are put into the same enclosure.

3. Set up a temporary cultivation area: before stocking, the temporary cultivation area is surrounded by the mesh of Muda 1.2cm, which accounts for 10% to 20% of the whole enclosed area, and the feeding management should be strengthened. When the aquatic plants sprouted and grew luxuriantly from April to May, the net was removed, and the crab species were allowed to crawl into the enclosed area to find food, so that the aquatic plants maintained a strong ability of regeneration.

4. Pre-stocking treatment: the crab species purchased from other places, together with the packing bags, are soaked in water to soak 2~3min, rinse off the foam and present for a moment, then soak 2~3min in water, repeat 3 times, wait for crab species to absorb enough water, then unpack, take out crab seeds for drug disinfection, generally soak 3~5min with 3% or 5% salt water or soak 10min with 10~20g/ cubic meters of potassium permanganate, and then put it into a temporary recuperation area.

Stocking time and method

The planting time of river crab is late December every year or before the end of March of the following year, and the water temperature should be 5-10 ℃, and it is best to release it at one time. The stocking specification is 150 million 200 crabs / 7500 million kg crabs per square hectare, and large commercial crabs can be obtained by the end of the year. In order to make full use of water bodies and food organisms, it can be matched with 75150 silver carp per square hectare, 150 bighead carp and 220 carps per square hectare, and 220 carps per square hectare with 15cm.

Maintenance and management of ecological environment in water area

1. Cultivate and transplant high-quality aquatic plants: aquatic plants are not only good bait for river crabs, but also places for their habitat, concealment and molting, and can purify water quality; summer can also prevent heat and cool down and promote the growth of river crabs. The river ditch itself grows some high-quality wild aquatic plants, which should not only ensure the growth and reproduction of these aquatic plants, but also be transplanted and replenished in a planned way. For example, collect bitter grass seeds in early winter, soak 10~15min in water and mix with soil, sow them all on the bottom of the river, sowing them 0.3-0.5 square hectares per kilogram of grass seeds; you can also take verticillium verticillata from other water bodies and cut them into small segments about 15cm and insert them into the bottom of the water; from February to March, you can transplant Rabdosia malayensis with 750~1500kg/ square hectares, divide them into small clusters and evenly insert them into the depths of 5cm with bamboo poles. In the process of culture, submerged plants should be kept below the surface 20~30cm, the excess parts should be cut off, the growth of water peanuts and Potamogeton crispus should be controlled, and the coverage rate of aquatic plants should reach about 80%.

2. Transplanting snails: snails can reproduce on their own at the bottom of the water, providing high-quality fresh bait for the growth of river crabs; at the same time, it can eat unicellular algae and organic detritus at the bottom to improve water quality. Every year before and after the Qingming Festival, fresh snails 3000~4500kg/ square hectares can be placed in the enclosure area.

3, reasonable feeding: in the whole breeding process, according to the different seasons, according to the principle of "front and back essence, middle green, meat collocation". The water temperature is relatively low from late March to May. When the fresh mixed fish are cooked and mixed with a small amount of wheat flour, they will be fed along the river in a lump, once a day at 2: 00 p.m., and the food intake will be 2% or 3% of the crab's body weight, or choose full-price grains and appropriately reduce the amount of feed. The water temperature rose in June and was fed twice a day, accounting for 30% of the daily dose at 8: 9 am and 70% at 5: 6 pm, when the food intake increased to 5% to 8%, mainly with small miscellaneous fish and full-price grains, with bean cakes, wheat, corn and so on. Early July to early September is the high temperature season, twice a day, mainly corn, wheat, broad beans, bean cake, pumpkin, potatoes, weeds and other plant feed, with pellet feed, daily feed volume of 3% to 5%, fresh feed of 8% to 10%. During the fattening period of river crabs in mid-September, animal feed should account for 60%, with plant feed 40%, and daily feed consumption should be 8%, 10%, and drop to 3% and 5% after mid-October.

4. Daily management: at the initial stage of crab stocking, the activity is more frequent and it is easy to escape. It is necessary to patrol the river and inspect the network every day to see if there are any escaped crabs. In the medium term, we should do a good job in wind prevention, flood control, and prevention of theft and damage, and diligently inspect, maintain, and remove floating objects such as water and grass, so as to ensure that the piles are neat and firm, the block is neat and without holes, the stone cages do not get out of the bottom mud, and the water flow inside and outside the net is smooth. In the later stage, due to reproductive migration, sexually mature river crabs will flee desperately, so we should strictly prevent river crabs from climbing and escaping from the top of the wall net, seize the opportunity to catch, and organize personnel to patrol the river to strictly prevent poaching.

5. Fishing and temporary cultivation of adult crabs: as the blocking facilities are limited to the inlet and outlet, anti-escape equipment can not be built on both sides of the narrow ditch, which requires that the fishing of river crabs should be carried out at the beginning of their natural reproductive migration, and the temporary cultivation of adult crabs should be done. The fishing time begins in late September, and various tools such as three-layer Gill nets, crab cages, set nets and other tools can be used to catch them or catch them by hand along the river at night. Adult crabs should be weighed and counted, separated by male and female according to specifications, and put into the pond for temporary breeding. Through artificial bait to promote fattening, careful feeding and management, timely listing, so as to raise crabs, sell good crabs, and achieve product value-added.