Research On Technique Of Healthy Aquaculture Of River Crab In Large Scale

Eriocheir sinensis Milne-Edwards, known as river crab, is a special product in China. Its main distributed fields include seaboard of the Donghai Sea and the Bohai Sea and offshore rivers and lakes. Since 1980s, the production of river crabs has gradually changed from natural fish to artificial culture, and its great production scale also becomes pillar industry of our country. This research report summarizes the river crab's important biological features like habitat, breeding and growth, and the general conditions of its distribution in the world and its artificial culture in China. It also discusses about potential problems and their solutions during aquaculture. The results of research shows that the beneficial results of industrial production of river crabs will take a step forward only if attention is paid to the quality of parental kind of merchandise crabs. Healthy aquaculture of crabs in large scale not only serves to the increase of yield and benefit, but also becomes a production mode that meets the need of uncontaminated food in recent markets. The basic principle is to realize healthy culture in large scale through improvement of selective kinds and regulation of ecosystem, and to culture uncontaminated crabs of bigger size and higher quality. Considering four major factors of crab culture (quality of kind, feed, water and bottom), and crucial technicalities like prevention of escape and prevention and cure of diseases, combined with sorts of experiments, demonstrations and conclusions, this research elucidates technical requirement and practical method of healthy culture of river crabs in large scale.Quality of kind-requirement of quality of parental crabs, means how to select and protect superior kind are cardinal requirements. Qualities of feed and water are material assurance of high productivity, which are related to the study of nutrition need of crabs, production of mixed feed and rational distribution of feed. The technical index sign should be in consistent with the technique standard of producing uncontaminated food, and the aqueous environment should comply with regulations of《Water quality of fresh-water culture》. Temperature of water is under control by means of growing water plant, conditioning water level and structural reform of ponds. Suitable temperature is between 15℃and 30℃, and the best is between 22℃and 28℃. Solute oxygen is no less than 5mg/L.Range of pH is between 7.0 and 7.9, and the best is between 7.5 and 8.5. Fit pellucidity is between 30cm and 50cm, and the best is more than 50cm. NH3-N should be less than 0.1mg/L and H2S shouldn't be sensed. Thickness of filthy mud is less than 10cm and the amount of nitrogenous materials in the mud is less than 0.1%. Bottom of ponds is the main habitat of crabs, and the environment in the bottom of river influences crab's growth significantly, which should be improved through clearing up, growing water plant and utility of microorganism to benefit prevention and control of diseases.As to the application and research of healthy aquaculture of crabs in large scale, after improving water quality with microorganism, the reporter finds that the utilization of feed by crabs increases, and the feed coefficient is reduced by 0.5, compared with results of the control pond in the corresponding period. At the same time, the livability of crabs increases by 8% and yield per acre increases by 10% after using the microorganism. There is no obvious increase of livability in rotation culture of carp and bighead, but the test pond produces merchandise fish with average size bigger than that of the control pond by 150g per fish. Through study of growing tape grass in pond, the reporter finds that there are manifest advantages of growing tape grass: the grass absorb nitrogen, phosphorus, heavy metals and help to reduce water temperature. The average size of each crab is bigger than that of control pond by 15g to 50g in the same conditions of raising density, which leads to a significant increase in benefit. To realize the healthy culture of crabs, it is also important to use proper drugs. According to the research, the test pots had cumulative morbidity of 30% at average in 2005, but in 2006, after promotion of healthy culture and usage of drugs, the morbidity was greatly reduced by 16%. Besides, bacteritic dropsy and black gill were also under control with a morbidity of 10.33%.In addition, based on the practical conditions of current production, this report lists some major problems involved in healthy culture of river crabs in large scale, and presents some available solutions and utilitarian methods.