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Causes and Prevention of Shivering Disease in Crab
In recent years, the occurrence of shivering disease in river crabs has been frequent. Once the disease occurs, it is difficult to cure. It often causes massive crab deaths. The hard-to-reach crabs are also undersized because they missed the best growth period, resulting in more than 50% of crab owners appearing. The loss restricts the further development of the crab industry. In response to the turbulent occurrence of the crab plague in recent years that has caused headaches for the aquatic industry, in 2003, the deployment of elite fisheries at the Haimen Aquatic Technology Guidance Station in Jiangsu Province will strengthen the crab shivering disease on the basis of analyzing the causes of the disease. Prevention and control of the prevention and control of research and guidance work, the mortality rate of shivering disease had a significant drop, the epidemic was basically controlled, a large area of ​​aquaculture outbreak shivering disease basically did not appear. First, the symptoms of the crab when the onset of the disease with the foot to prop up the entire body squat on the water or aquatic plants (and some climbed ashore), mouth spit bubble, large sag, whole body jitter, so called "shivers." Second, the cause of the disease At present, there are many forms of crab farming, and the causes of the disease vary. However, the monoculture of ponds and the lack of water and grass cultivation in the ponds have a higher incidence of fish and crab mixed ponds, and the relative loss is relatively large; the incidence of rice paddy cultivation and river ditch cultivation is low. The incidence of shivering disease is mainly due to the following reasons: 1. Poor seed quality is poor. Firstly, due to the rapid expansion of river crab breeding scale in recent years, the quality of Yangtze River water crab species is scarce, and poor quality crab species flood the market. Farmers cannot distinguish crab species. The merits and demerits of the project included the purchase of some poor-quality crab species that have unexplained roads, long-distance traffic, incomplete limbs, and poor health and are prone to cause crab disease. Second, in order to pursue benefits, coastal nursery manufacturers illegally used drugs in the breeding process and used excessive amounts of antibiotics. Thirdly, the use of parent crabs in the affected area for nursery seedlings causes the seedlings to carry pathogenic bacteria and is prone to disease. 2. Disinfection is not thorough or not at all Sterilization in crab breeding production includes the disinfection of crab species, water bodies, and bait. The first is that the crabs are placed in the pool without selection and disinfection and cause shivering. Second, disinfection of aquaculture waters is not complete. With the increase of intensive culture, in the high-density culture ponds, the decomposition of crab excrement and some fish and crab corpses will lead to the proliferation of microorganisms that threaten river crabs and some disease intermediates. If you do not regularly sterilize the water body, it is the inevitable result of self contamination and illness. Third, when feeding fresh animal baits (such as snails, small fish, shrimp, etc.), they are often directly fed without disinfection, which increases the risk of harmful organisms on river crabs. There are often residual foods in the food or feeding sites. If they are not removed in time, the spoilage will provide favorable conditions for the propagation of pathogens. This situation is most likely to occur in high water temperatures, eating habits, and epidemic seasons. 3. Deterioration of ecological environment in aquaculture waters With the rapid development of crab farming, the ecological environment in aquaculture waters has deteriorated. The main reasons are: a long-term pond is not clear, making pond mud deposits serious, eutrophic water quality; two stocking density is too high, making high-quality aquatic resources depleted, poor quality water plants go crazy; three rapid development of township private industry in recent years, a large number of industrial wastewater Emissions into rivers cause widespread contamination of waters. Deterioration of the water environment is an important cause of shivering in crabs. 4. Feed nutrient insufficiency and feeding improper feed is the material basis for the growth of crabs. The quality of the bait directly affects the growth and development of crabs and thus affects the crab's ability to resist diseases. For a long time, the majority of farmers have been feeding wheat, corn, hawthorn and small junk fish, crayfish, etc. What feed is cheap, what is the source of feed, does not consider nutrition, and the number of feeding is not very particular, so often Causes water pollution and induces crab disease. 5. Infected disease through the drainage into the drainage is not smooth enough or there is no independent access to the drainage channel, resulting in a pool of disease, adjacent to multiple pool infections. Third, control measures 1. Seed prevention (1) crab farmers when buying crab species should pay attention not to purchase large eye larvae in the disaster-hit area, deduct crabs, manufacturers can not buy parents in the ward; less than workshop-style small The purchase of seedlings by the manufacturer should be carried out by a licensed manufacturer backed by a scientific research unit. (2) Farmers should insist on self-education and autotrophic crab cultivation, develop healthy crab species, and improve disease resistance of crab species. Buy local seedlings as much as possible to cultivate seedlings. It is advisable to use a 3% to 5% salt solution for disinfection for 5 minutes or a 15ppm formalin solution for 15 minutes before entering the pond. (3) In a pond, it is best to put enough crab species of the same size and same source at the same time to prevent the species from being mixed in the same water body with multiple species and multiple specifications to reduce the chance of mutual infection. 2. Drug Control Before stocking crabs, ponds and crabs must be sterilized with drugs to minimize the impact of pathogens. Add a certain amount of terramycin, ciprofloxacin and other antibiotics to feeds for internal use and prevent disease. During the breeding process, chlorine dioxide and other disinfectants are regularly used to disinfect the body of the water, and lime is used to improve the quality of the water. The amount of lime used is 7 kg to 8 kg per acre and the water is splashed with hot water. On the one hand, the bacteria can be killed and the river crabs can live in good conditions for a long time. On the other hand, calcium ions can be provided to promote smooth shelling and rapid growth of crabs. 3. Strict management and prevention In day-to-day management, it is necessary to strictly manage and intensify management, timely and accurately detect the condition of the disease, and achieve the right remedy. Adhere to the daily tour ponds and find the diseased crabs should immediately diagnose the cause and isolate the pool treatment. It was found that the dead crab was buried immediately after identifying the cause to prevent the water body from reinfecting. Strict operating procedures, especially in the peak period of shivering disease, should be well cleaned and disinfected feeding tools to avoid cross-infection. Strengthen the management of water sources, eliminate the application of circulating water in the cultivation of crabs, realize the separation of water and sewage, prevent the occurrence of a pool, and harm the nearby crab ponds. When feeding, it is necessary to ensure that the bait is fresh and palatable, that no corrupted feed is thrown and that the bait is removed in time. If conditions permit, full-price compound feeds can be used. Feeding full-priced compound feeds can increase the disease resistance of crabs. 4. Ecological prevention and control Creating a good ecological environment and implementing ecological prevention of crab disease is an effective method for preventing shivering disease. (1) Renovation of Tangkou and thorough cleaning of the pond The technical renovation of the crab pond will be implemented so that the two channels can be realized in the drainage and drainage. The bottom of the pool is flat and has a certain slope. The silt thickness at the bottom of the pool is less than 15 cm. After each year of crab fishing, clear lime (150 kg/mu) or tea pot is used to completely clear the pond, and the bottom of the pool is fully exposed to promote the mineralization and decomposition of organic matter at the bottom of the pond and improve the sediment quality of the pond. (2) Planting aquatic plants and simulating natural habitats The crab ponds should be transplanted with more aquatic plants such as water peanuts, elegans, and bittergrass. On the one hand, they should provide high-quality vegetal food for crabs, and on the other hand, they should stimulate the natural habitat environment. Its shelling grows. Aquatic grasses preferably cover more than 30%. (3) Water Quality Regulation of water quality is directly related to the occurrence and spread of shivering disease in river crabs. Summer and autumn high season to deepen the pool water, keep the water level in the 0.8 meters to 1.2 meters, ground change pool water, flush water once a week, both to prevent water quality deterioration, aging, but also promote crab shelling growth. It is also necessary to regularly measure the physical and chemical factors such as pH value and transparency of the water to adjust the water quality in time. (4) Promote ecological crab cultivation and promote healthy crabs. Actively promote ecological crab cultivation measures. Combine methods such as raising crabs in rice fields, raising crabs in rivers, and raising crabs in grasslands to create ecological factors that are suitable for the growth of crabs and prevent them from interacting with each other. Shivering disease. In the intensive culture of crab ponds, we actively promote healthy breeding techniques such as polyculture of fish and crabs, and integrated culture of fish, shrimp, and crabs. Choosing a reasonable stocking density, appropriately reducing the crab yield, and reducing the impact and destruction of the crab itself on its living environment are effective measures to control the occurrence of disease. Moderate nesting of a small number of ferrets such as white plover or squid, black plover and other ferocious fish to remove residual baits, purify water, prey on diseased fish, diseased crabs, and prevent crab disease. Rational feeding and correct mastering of "four-determined" and "four-viewing" feeding techniques, fully meet the nutrition needed for growth and development of crabs, and improve their resistance to diseases. (5) Replacing crabs in ponds where crabs are severe can be replaced by rotations. Rotations are performed every 2 to 3 years. The use of biological interactions and the replacement of ecological environments suppresses viruses and bacteria, thus preventing the occurrence of shaking. The purpose of fester. (6) Putting Photosynthetic Bacteria A certain number of photosynthetic bacteria were placed in intensive culture ponds to make them fully grow and develop in ponds and form dominant populations. Photosynthetic bacteria can promote the decomposition of mineralized organic waste, reduce the concentration of harmful substances in the water, clarify the water quality, keep the water clear and tender, and effectively promote the growth and development of beneficial microorganisms. The use of biological antagonism to inhibit the growth and development of pathogenic microorganisms to achieve the purpose of preventing crab disease.