Culture Technology of Large Size River Crab

Crab is favored by consumers at home and abroad for its rich nutrition and delicious meat taste. At present, river crab has become the main aquaculture species in various places, and river crab aquaculture has changed from "big crab culture" in pursuit of yield to "ecological crab culture" centered on quality and benefit. The ecological culture techniques for cultivating large-sized river crabs mainly include:

Select fine breed and control the quality of bred crab

Large size crab must have high quality crab species as the basis. Choose self-bred or locally bred long-carrying water system healthy, disease-free and injury-free, regular specifications, sound appendages, shiny, active juvenile crabs as crab species, avoid using juvenile crabs of unknown origin, which is the most important factor for breeding large crabs and improving survival rate. Generally, high-quality crab species can be selected from three aspects: from the appearance, body shape, foot, forehead teeth and other physiological characteristics to identify crab species in the Yangtze River system; eliminate the sexually precocious "small crab" without breeding value, the so-called "small crab" refers to the first-year young crab, weighing 10~35g, reaching sexual maturity, growth stagnation, death one after another; from the foot incomplete degree, seed activity, body surface has no cattle worm to select healthy high-quality crab species.

Planting aquatic plants to create a good ecological environment

As the saying goes,"crab size, look at the grass." Aquatic plants are planted in the culture water area of adult crabs, firstly, the aquatic plants are used as natural high-quality plant feed for crabs; secondly, the aquatic plants provide a hidden place for the crabs to perch and molt, so that the crabs are not easy to be discovered by enemies and reduce mutual killing; thirdly, the photosynthesis of the aquatic plants can increase the dissolved oxygen in the water, absorb organic matters in the water body, prevent the water quality from being nourished, play a role in purifying the water quality, keep the water quality fresh and improve the culture environment of the water body; Fourthly, aquatic plants can play a role in shading and cooling in high temperature season, which is beneficial to the growth of river crab. The variety of aquatic plants planted should not be single, but diversified. It is best to combine submerged plants, emergent plants and floating plants, and distribute them reasonably to meet the needs of river crab in many aspects. Submerged plants can be selected from bitter grass, verticillata verticillata, Elodea, etc., emergent plants such as reed, Zizania latifolia, etc., floating plants such as duckweed, etc. The planting area of aquatic plants in crab breeding waters should account for 50-60% of the water surface area. July to August in summer is the peak period for crab to ingest aquatic plants, so close attention should be paid to ensure both the utilization of crab food and the high storage capacity. When not enough, measures should be taken to supplement the aquatic plants, but the aquatic plants should not be caught too much. The rotten aquatic plants are easy to cause water quality deterioration and induce crab diseases. Too many aquatic plants, especially too many single species similar to Elodea, are easy to cause the bottom water to stop flowing, resulting in the deterioration of the bottom water. The water channel should be drained in time to facilitate the flow of water in and out of the crab pool, otherwise it is easy to cause black gills, edema and other diseases.

Control stocking density, pay attention to reasonable mixed culture

The stocking density of crab species is related to crab species specifications, breeding conditions, marketing requirements, management level, etc., and a two-year breeding mode can be adopted, that is, crab seedlings are purchased at the end of May and the beginning of June, extensive breeding is carried out in the pond, and buckling crabs can be bred at the end of the year. In the spring of the second year, these buckling crabs are put into the pond. Generally, the stocking specification of crab species is 100-200/kg. 300-500 crabs per mu of water surface can be released properly to improve the specification and quality of river crab. Adult crab ponds dominated by river crabs cannot be mixed with herbivorous fish (grass carp, megalobrama amblycephala, etc.), omnivorous fish (carp, crucian carp, tilapia, etc.), carnivorous fish (snakehead, catfish, bass, etc.), but only some filter-feeding negative species (silver carp, bighead carp, etc.). Its purpose is to remove plankton from the water and prevent deterioration of water quality. However, due to the large number of aquatic plants in the crab pond and the thin water in the pond, the number of polyculture should not be large. Generally, 50-100g/tail of silver carp and 40-50 bighead carp species are mixed in each mu of water surface (the ratio of silver carp and bighead carp is 5:1). In addition, the crab culture pond cannot be mixed with turtle. If conditions permit, the culture mode of mixed culture of appropriate amount of shrimp in crab culture pond can be adopted. With ecological culture management measures, high yield, high quality and high efficiency can be obtained.

Snail feeding to meet the needs of crab for bioactive substances

Snail is the most favorite fresh animal bait for crab. Snail benthos, slow action and strong water purification ability. In adult crab culture pond, put 150~250kg of live snail per mu of water surface to stop its natural reproduction, so as to provide continuous palatable and active protein bait for the whole growth process of crab. In all kinds of snails can be selected in freshwater snails breeding individuals in the largest fine varieties-apple snail. Apple snail is also called apple snail, thin shell, large individual, high meat content (edible ingredients account for 38% of body weight), miscellaneous food, fast growth, long reproduction period, high multiplication multiple. Transplanting apple snail into crab culture pond can not only keep the water quality of crab pond fresh, but also provide natural food rich in various bioactive substances for crab, promote rapid growth of crab and improve the market size of adult crab.

Regulate water quality and promote healthy growth of crab

The crab has higher requirements on water quality, requiring that the dissolved oxygen in the water be maintained at 5mg/L, pH 7-8.5, transparency 30-40cm, and the water level in the four seasons should be shallow in spring, deep in summer, autumn and winter, so as to maintain a good water environment with good water quality, vitality, tenderness and freshness in the crab pond and promote the healthy growth of crab. In the breeding process, we must adhere to regular water injection, early every 10-15 days to change the water once, each time 1/3 of the water. In order to ensure fresh water quality in high temperature season, add some new water every day and change the water twice every week. In addition, every 15-20 days with quicklime 8-10g per cubic water splash, if there are conditions, it is best to regularly use photosynthetic bacteria or EM bacteria and other microbial agents of water splash, improve water quality.

Do a good job in crab disease prevention and control

In recent years, with the continuous expansion of crab culture scale, crab disease is also spreading and upgrading. Crab disease, which has never existed before, occurs in large numbers now, mainly ciliate disease of juvenile crab and shaking disease of adult crab, which brings huge economic losses to crab culture industry. Therefore, crab disease prevention and control should adhere to prevention first, early detection, early treatment, no disease first prevention, early treatment of disease, in different growth stages to take different methods for prevention. Photosynthetic bacteria, EM bacteria and other microbial preparations are selected to regulate water quality. High temperature season regular use of quicklime, dibromohydantoin and other prevention. In the high incidence period of ciliates, the insecticides should be used alternately every 15-20 days. Tremble is a kind of microorganism between bacteria and virus. Using enemy to kill clear pool is an effective method to prevent and cure shake disease.