Key Technical Points for Winter Disease Prevention and Control in River Crab
Clear the sludge at the bottom of the pond
The main components of sludge are large amounts of residual bait, organic matter, dead animal carcasses and biological excrement. Excessive sludge easily leads to deterioration of water quality in summer, and also produces large amounts of organic acids, hydrogen sulfide, ammonia, etc., which inhibit and harm the growth and survival of river crabs. In particular, pathogenic microorganisms such as bacteria and parasites exist in the sludge, and once conditions are suitable, various pathogens can cause widespread outbreaks. Therefore, taking advantage of the idle period of crab ponds in winter, drain the pond water completely and remove all the sludge at the bottom of the pond using machinery or manual labor.
Freeze and sun-expose the pond bottom
After the crab pond is cleaned up, straighten the water channels and use machinery to pump water regularly, so that the pond bottom undergoes severe freezing and sunlight exposure for about 1 month as much as possible, in order to improve the soil conditions at the pond bottom, allow some pathogens to be killed by freezing and sunlight exposure, and create a good ecological environment for the future growth of crabs.
Build a proper inlet and drainage system
In addition to considering sufficient water flow, water physicochemical factors suitable for crab growth, and freedom from pollution and pathogens, attention must also be paid to cross-contamination and repeated infection caused by using the same channel for both inlet and drainage. Therefore, each crab pond is required to be able to drain its pond water independently.
Carry out chemical disinfection
20 days before stocking crab seedlings, strictly disinfect with quicklime, bleaching powder, etc. For quicklime disinfection, use 75-100 kg per mu, dissolve the quicklime in water and splash it over the entire pond; for bleaching powder disinfection, use 15-20 kg per mu.
Disinfect the crab bodies properly
Before the crab seedlings are put into the pond, disinfect with appropriate chemicals. Commonly, soak in potassium permanganate solution at a concentration of 15-20 mg per liter for 20-30 minutes, or soak in bleaching powder solution at a concentration of 10 mg per liter for 10-15 minutes.
Transplant aquatic plants
Aquatic plants can provide river crabs with habitats and environments for molting, and can also provide them with fresh and palatable plant-based feed while reducing the ammonia nitrogen content in the water, increasing oxygen and improving water quality. Among aquatic product varieties, submerged plants include Vallisneria (tape grass), Najas minor, etc., and floating plants include water hyacinth, duckweed, etc. These plants must be sown, transplanted or relocated in winter and spring, so that the coverage rate of the crab pond is above 60%.