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1 Technical measures
1.1 Geographic Conditions
Doumen District is located in the mouth of the Xijiang River in the Pearl River Delta. Most of the aquaculture ponds in the region are freshwater ponds. There are a large number of salty deposits in areas under 10 meters in diameter. Drilling holes can be used to extract salt water with a salinity of 15‰-20‰.
1.2 Pond conditions
The ponds for rearing South American white prawn are mostly ponds that were originally cultured with Macrobrachium rosenbergii, and a small part of them are ponds for rearing quaternary fish. Each area of ​​6-8 acres, depth of 1.5-2 meters. The pond is pumped and drained with a pump.
1.3 Restocking operations
1.3.1 Clear water can be obtained by conventional methods, such as throwing 150 kg lime dry pond per acre, inhaling water 0.5 meter, and then disinfecting once with 30 g/m3 bleaching powder, then using a single cell algae to promote Long prime or compound fertilizer water. However, the ponds should be washed between the two rivers. After the ponds were used, the water was used to wash away the silt. At the end of the year, the ponds were allowed to leave the ponds. After the exposure, the mud was removed with a bulldozer.
1.3.2 Adjusting salinity in ponds Penaeus vannamei has a wide salinity and can grow in freshwater with little salinity, but it has higher salinity in the early stage of cultivation and gradually fades later, so it is necessary to pour the pond water before the seedlings are planted. Salinity adjusted to more than 5 。. There are three methods of adjustment: First, dig the wells, adjust the salinity of the pond water with saline water in the ground; second, adjust the salinity by using seawater to transport the seawater; third, adjust the salinity by using sea salt or seawater.
The adjustment of the salinity of the shrimp ponds is not consistent with that of the whole pond. The salinity of the small water bodies used for the crude seedlings used in the ponds is higher than that of the outside, which serves to save the cost of water transfer and gradually dilute the water.
1.3.3 After disinfecting, fertilizing, and adjusting salinity, the original pond desalinated coarse-grained seedlings shrimp ponds should be enclosed in a plastic sheeting to form a small 10- to 15-m2 water body on the convenient side of management. The salinity should be adjusted to be close to the salinity when the larvae are desalinated, usually at 8 ‰. the above. The shrimp seedlings should be healthy and lively, and require to be diluted to less than 10‰ on departure, with 50,000 seedlings per mu. The returned shrimps should first be kept in a small body of water for about 10 days. The benefits are not only centralized, but also facilitate the management of feeding, but also play a role in continuing to dilute and improve the survival rate. Shrimp will gradually decrease its salinity during the holding of small water bodies. After 10 days, the cloth will be removed and the shrimp will grow into big ponds.
When temporarily raising the standard crude shrimp seedlings in small water bodies, multiple oxygen enrichment heads should be placed to prevent the shrimp seedlings from being intensively deficient in oxygen; appropriate feed of microparticle feeds or shrimp slices should be adopted to promote the growth of shrimp seedlings.
1.3.4 Use of Beneficial Microbiological Agents Apply microbial preparations once every 15 days from the time of seedling injection, each time about 1 kg, taking care to prevent conflicts with the disinfectant (refer to the product instructions). Microbial preparations have the effect of degrading ammonia nitrogen and can be used in combination with simple algae stimulating hormones to keep the water fresh. Avoid excessive water changes, reduce spending on salting, and keep shrimps growing steadily.
1.3.5 Other management maintains adequate dissolved oxygen. In addition to good green algae cultivated in the water, one 1.2-kilogram aerator is placed on every three acres of water. Feed pellet feed with a feed coefficient of approximately one. Higher dedicated shrimp feeds, which can be used in later period with Macrobrachium rosenbergii feeds, the pH of the culture waters should be kept at 8.0-8.5, more than 9.0 shrimps are easy to attack; water quality in the breeding process is not particularly corrupted Generally do not have to change the water in order to maintain the salinity of the water and the content of beneficial bacteria; under normal circumstances the pond water does not have to be disinfected, each use of antibiotics brings destruction of the aqueous phase, increase the possibility of shrimp stress illness.
1.3.6 Timely Harvest In the summer and autumn, the breeding period reaches 100 pigs per kilogram in 70 days, which can be selected for market. The breeding time is 70-80 tails per kilogram for 100 days. Usually the listing is completed. Timely listing can avoid the loss due to the deterioration of the aquaculture environment in the later period.
2 Conclusions and Analysis
(1) The comparison of the culture of P. vannamei in freshwater ponds after aquaculture with aquaculture in coastal seawater ponds may be due to the avoidance of horizontal infections of similar viruses in crustaceans and copepods in seawater, and the blocking of P. vannamei in seawater. Causes of toxic diseases from seawater induce stable production. This point has also been proven in the production of this region. In the distribution of South American white shrimps throughout the region, the more disease near the beach, the more disease and the lower the yield. In 2001, there were only 84 tons of shrimp in 3000 acres of shrimp ponds. The average yield per mu is only 28 kilograms, and there is only 8 kilograms of per annum near the southernmost pond. More than 500 kilograms of production are in the pure freshwater pond area in the north.
(2) The use of beneficial microorganisms in large quantities is one of the indispensable conditions for the culture of Penaeus vannamei. During production, it was found that most of the white shrimps in South America are caused by unstable water quality or some kind of external stress, and they first develop bacterial infections and induce latent viral diseases. Maintaining water quality and environmental stability are important ways to prevent disease outbreaks. The use of microbial preparations can control excessive ammonia, nitrites, hydrogen sulfide, and other harmful substances in the water, thereby preventing widespread damage and allowing healthy growth of the cultured shrimp in a fresh and stable water environment.
(3) Controlling drug use is one of the effective methods to prevent the outbreak of shrimp disease. Penaeus vannamei can cause morbidity for many reasons. At this time, if a large number of antibiotics are used to disrupt the balance of the culture water, such as the death of algae, the degree of stress in the shrimp will increase, which will further worsen the disease. The correct approach is to pay attention to maintaining the stability of water quality when there is not a lot of shrimp, and there should be no sudden changes to recover; if the disease expands, some milder drugs such as bromochlorohydantoin can be used to disinfect and treat the disease. It is not necessary to repeatedly administer drugs to prevent the disease from expanding. After 3-5 days of application, microbiological preparations should be re-introduced to create a good water quality environment in order to slow the disease.
High-yielding aquaculture technology of Penaeus vannamei in estuarine area
Doumen District, Zhuhai City, is located at the mouth of the Pearl River and is rich in freshwater resources. It adopts “dilution + beneficial microorganisms†to implement semi-enclosed cultivation of Penaeus vannamei. It has been harvested in large areas for three consecutive years, providing some useful references for aquaculture areas with similar conditions.