Prevention of hepatopancreatic necrosis disease in shrimp
Hepatopancreatic necrosis disease often causes mass death of shrimp from stocking to 45 days of age. To limit this disease, farmers need to pay special attention to preventive measures.
Release with other species
For large areas, black tiger shrimp should be raised in an improved extensive form, with a density of 7 - 10 shrimp/m2. When raising, it is necessary to add tilapia, mullet, and crab (1 shrimp/2 - 3 m2). According to Professor Donald Lightner - University of Arizona (USA), raising shrimp with other species has a much higher level of disease safety than raising monoculture shrimp. These species will destroy harmful species to protect the natural balance, which means that disease-causing bacteria will be destroyed and shrimp will not eat these bacteria, so they are less susceptible to disease.
Pond preparation and water treatment
Vibrio parahaemolyticus bacteria is the main cause of hepatopancreatic necrosis disease in shrimp and will develop very quickly when conditions are favorable. Therefore, after each crop, the bottom mud of earthen ponds must be dredged and limed for disinfection. If the bottom of the pond still has a lot of black mud after dredging, clean sand can be pumped into the pond (15 cm thick or more) to prevent the mud layer from creating toxic gas (H2S) and stabilize the water temperature. For ponds covered with tarpaulin, after each crop, it is necessary to use a pump to clean it, use Chlorine (40 - 50 ppm) to spray on the tarpaulin surface, dry it for 2 - 3 days before supplying water. The pond banks should be covered with nets to prevent crabs and clams from entering. The water supply and drainage ditches for the pond need to be dredged and disinfected after each crop.
In order to kill all pathogens and disease-carrying hosts, water is supplied to the settling pond, treated with chlorine (10 - 15 ppm), and aerated for 3 consecutive days to evaporate all chlorine before being supplied to the pond through a thick filter bag. On the other hand, it is possible to use an ultraviolet sterilization system to provide clean water for the pond and limit chlorine residue. After taking water into the pond, it is necessary to check environmental factors such as salinity, pH, alkalinity, toxic gases, etc.; After that, shrimp larvae (size P12 or larger) are released and must be quarantined to ensure they are disease-free.
Other measures
Research results show that hepatopancreatic necrosis disease rarely occurs at low salinity (below 10‰), so when stocking, the water must be maintained at 15 - 20‰ salinity; then, add fresh water to gradually lower the salinity to below 10‰. Because the bacteria that cause hepatopancreatic necrosis disease prefer to develop in the pond bottom environment, when preparing the pond, it is necessary to design a low-lying area to collect waste in the middle of the pond (1 - 2% of the area) and periodically siphon (5 - 7 days/time) to keep the pond bottom clean.
According to Professor Donald Lightner, after pond water is treated, Vibrio parahaemolyticus bacteria will recover much faster than beneficial bacteria. Therefore, after 10 days of stocking, it is necessary to use biological products to promptly supplement beneficial bacteria, to restore the diversity of the bacterial community, suppressing the growth of pathogenic bacteria.
An effective measure to prevent hepatopancreatic necrosis in intensively farmed whiteleg shrimp is to design a cage in a shed, with an area of 100 - 500 m2, spread a tarpaulin on the bottom, around the bank, install an aeration system at the bottom, clean water, depth of 1 - 1.2 m. Shrimp are released in the cage at high density (400 - 500 shrimp/m2), environmental factors are controlled and waste is siphoned daily. Shrimp live in the cage, the environment is always suitable and not affected by the weather outside, so they rarely get sick. After a month, the shrimp are transferred to a normal large pond.
At the same time, in order to limit this disease, the use of Biofloc biotechnology to diversify the biological population in shrimp ponds is also of great interest. However, with this technology, maintaining the Carbon/Nitrogen balance in the water at 1/12 - 15 is not simple and it is also difficult to distinguish between beneficial and harmful bacteria in the growing bacterial population.
According to Thuysanvietnam