Breeding and Breeding Technology of Rice Crab in South China

The crab is popular with domestic and foreign consumers for its rich nutrition and delicious meat. At present, river crabs have become the main aquaculture species in various regions. The crab breeding industry has been transformed from the “large crabs” that pursue yield to the raising of large crabs and the “ecological crabs” centered on quality and efficiency. With the development of the crab breeding industry, crabs with small specifications and poor quality are increasingly not welcomed by consumers. Big size crabs not only sell smoothly, but also have an absolute price advantage. The market price of large size crabs is 3 to 4 times higher than that of small size crabs, and 120 to 160 yuan/kg more than 150g, while the specifications are only about 75g. 30 ~ 40 yuan / kg, but how to cultivate pollution-free production of large-scale crab is a breeder's concern. The so-called large-size crab refers to a crab that has a weight of 150g or more and has "green back, white belly, yellow hair, and gold claws." Through the summarization of many years of production practices, the major breeding techniques for breeding large-scale river crabs are:
First, select good breeds, and put good-quality crab species in large-scale crabs must have high-quality crab species as a basis. Choose the self-fertilized or locally-cultivated Yangtze River water system for the development of crabs that are robust, disease-free and harmless, have neat specifications, have appendages, and have good appetite, dexterity, and strong activity. Avoid the use of juveniles of unknown origin. This is the most important factor in raising crabs and raising the survival rate. Generally, high-quality crab species can be selected from three aspects: identification of crab species in the Yangtze River system from appearance, body type, step-foot, and prefrontal teeth, etc.; “Small Dumpling Crab” refers to the first-instar crab of the year. It weighed between 10 and 35g and reached sexual maturity, stagnant, and died one after another. It was selected from the degree of foot-foot incompleteness, the activity of seedlings, and the presence or absence of parasites on the body surface. High-quality crab species.
Second, planting aquatic plants, creating a good ecological environment As the saying goes, "Crab size, look at aquatic plants." The planting of aquatic plants in the aquatic crabs is a natural, high-quality botanical feed for crabs. The second is to provide habitats for crabs and shelters for clam shells. It is not easily found by predators and reduces the mutual killing. The third is the photosynthesis of aquatic plants. It can increase dissolved oxygen in water and absorb organic matter in water to prevent water quality from eutrophication. It can play a role in purifying water quality, keeping water fresh and improving water culture environment. Fourth, aquatic plants can provide shade cooling in high temperature season. The role of beneficial crab growth, planting aquatic species should not be a single species, to be diversified, the best submerged plants, emergent plants and floating plants combined with each other, a reasonable distribution to meet the various needs of river crab. Submerged plants can be selected species such as Vallisneria, black leaf algae, Elodea, etc., emergent plants such as reeds, alfalfa grass, floating plants such as duckweed and so on. The area for planting aquatic plants in crabs should cover 50% to 60% of the surface area. The summer of July-August is the peak period for crabs to ingest aquatic plants. It is necessary to pay close attention to ensure that crabs are used for food and eat, but also have a high storage capacity. When it is not enough, we must take measures to make up for the aquatic plants. However, weeds should not be caught too much. Corrupt plants may cause water quality deterioration and cause crab disease. Excessive amounts of aquatic weeds, especially those that are similar to Elodea, can easily cause the bottom water body to not flow and cause the bottom water to deteriorate. The water channels should be cleared out in time to facilitate the flow of water into the drainage and improve the water quality of the crab pool. Prone to black spot, edema and other diseases.
Third, control the stocking density, pay attention to reasonable stocking density of crab species, crab species specifications, feeding conditions, listing requirements specifications, management levels, etc., can take two-year breeding mode, is the end of May at the beginning of June to purchase crab seedlings, Extensive breeding in the pool, the end of the year can be bred into crabs, the second year of the spring and then put these crabs to the pool, usually the crab species stocking specifications of 100 to 200 / kg. Each 667 square meters of water stocking 300 to 500, take appropriate release, can improve the crab out of the pool specifications and quality. Crab ponds mainly composed of river crabs cannot be mixed with herbivorous fish (grass carp, group head locust, etc.), omnivorous fish (carp, clam, tilapia, etc.), carnivorous fish (black sea bream, carp, carp And so on), but only mixed filter-feeding fish (eel, squid, etc.). Its purpose is to remove plankton in the water and prevent deterioration of water quality. However, due to the large amount of aquatic plants in the crab pool, the pool water is thinner, so the amount of polyculture should not be much. In general, every 667 square meters of water surface polyculture 50 ~ 100g / tail white bream, bream species 40 to 50 tail (cod, squid ratio of 5:1), in addition, the crab pool can not be mixed, if conditions permit Adopting a mode of breeding of appropriate amount of fresh shrimp in crab ponds and using ecological breeding management measures to achieve high yield, high quality, and high efficiency.
Fourth, put snails to meet the needs of river crabs for biological active substances Snails are the most favorite live fresh bait of crabs, snails benthic, slow action, strong water purification capacity, in the crab pond, every 667 square meters of water The live snails 150 to 250 kg are put to let them breed naturally. This will provide a steady stream of palatable and active protein baits for the whole growth process of crabs. Among the various snails, apple snail, one of the finest varieties of individual species cultivated in freshwater snails, can be selected. Apple snails are also called snails. They have thin shells, large individuals, high meat content (38% of body weight of edible ingredients), high food habits, rapid growth, long breeding seasons, and high proliferation times. Transplanting apple snails in crab ponds can both maintain fresh water quality in crab ponds and provide natural foods rich in various biologically active materials for river crabs, promoting rapid growth of crabs and increasing the market size of adult crabs.
Fives. Regulation of water quality, promotion of healthy growth of river crab Crabs require higher water quality, require dissolved oxygen in the water to maintain at 5mg/L, pH value of 7 to 8.5, transparency of 30 ~ 40cm, the water level throughout the year to be shallow, summer, In autumn and winter, keep a good water environment where crab pond water quality is good, live, tender, and cool, and promote healthy growth of crabs. In the breeding process, we must adhere to regular water injection, change the water every 10 to 15 days in the early stage, change the water every time 1/3. In the hot season, to ensure that the water is fresh, add some fresh water every day, and change the water twice a week. In addition, every 10 to 20 days, quicklime 8 to 10g/m3 of tap water is used. If conditions permit, it is advisable to periodically use photosynthetic bacteria or microorganisms such as EM bacteria to sprinkling water to improve water quality.
VI. Preventing Crab Diseases In recent years, with the continuous expansion of the crab population, crab disease has continued to spread and escalate. Crab disease, which has never existed before, has now occurred in large numbers, mainly cilia of young crabs. Insect disease and shivering of adult crabs have brought huge economic losses to the crab industry. Therefore, the prevention and control of crab disease should be based on prevention, early detection, early treatment, disease-free prevention, disease early treatment, and different methods of prevention at different stages of growth. Select photosynthetic bacteria, EM bacteria and other microbial preparations to regulate water quality. Regular use of quicklime, dibromohydantoin, etc. is recommended during the hot season. Ciliate nets or ciliate net insecticides are used once every 15 to 20 days in the high incidence period of ciliate, and drugs should be used interchangeably to avoid drug resistance. Shiver disease is a kind of microbe that lies between bacteria and viruses. The use of enemy killing Qingchi is an effective method to prevent shivering disease.

Goji Polysaccharides is a rare plant polysaccharides containing protein, which have side chains of polysaccharide composed by six carbon sugars (rhamnose, arabinose, xylose, mannose, galactose, glucose) and main chains of protein composed by 18 kinds of amino acids. The glycoproteins with biological activity is a high-strength immune enhancer.

Wolfberry products with stable quality are all natural, safe, sanitary and fast absorption.Lycium barbarum polysaccharide extraction and purification is divided into two steps. First, the extraction of Chinese wolfberry crude polysaccharides, the second is purified Lycium barbarum polysaccharide. Crude polysaccharides extraction process is as follows: Weigh dried crushed medlar, petroleum ether: acetone (1: 1) reflux degreasing, the solvent was filtered off, the residue was air-dried 80% ethanol off monosaccharide and oligosaccharides. 
The polysaccharide is extracted by water after dissolving the residues such as oligosaccharides in water at 90-100 DEG C, the extract is concentrated under reduced pressure, the polysaccharides are precipitated by ethanol, the precipitates are washed with anhydrous ethanol and acetone, and the lycium polysaccharides are dried under vacuum. The crude polysaccharide is purified by passing the Lycium barbarum polysaccharide through a column of DEAE cellulose with different concentrations of NaCl as an eluent, concentrating the eluates with different salt concentrations respectively under reduced pressure, desalting them by dialysis, and then lyophilizing them differently Grape Lycium glycoprotein.

Modern medical research suggests that wolfberry polysaccharides can improve human immunity and have functions as anti-cancer, cancer treatment, hematopoiesis, liver protection and hypotensive, free radicals removal , anti-fatigue, anti-radiation, and cell activity improvement; Goji polysaccharides can control cells division& differentiation, and regulate cell growth & aging, which is widely used in the pharmaceutical, health food and other fields.

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