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Ecological farming techniques for managing stocking densities through the polyculture of crabs, shrimp, and fish, along with the planting of aquatic plants and snail transplantation, involve six key components. These methods not only improve productivity but also ensure a sustainable and eco-friendly aquaculture system.
First, pond conditions are crucial. The pond area should be between 2 to 10 mu, with an average water depth of 1 to 2 meters. The pond bottom must be flat and free from excessive silt, with a solid, leak-proof structure. The surface width is around 2.0 to 2.5 meters, and the soil must meet national standards (GB15618-1995) for environmental quality.
Second, water sources need to be clean and free from industrial, agricultural, or domestic pollution. The water quality should comply with the Ministry of Agriculture’s standard NY5051-2001 for freshwater aquaculture. Reducing water discharge into rivers helps prevent environmental contamination.
Third, anti-escape facilities are essential. Using materials like aluminum sheets, thick plastic films, or calcium plates, these structures should be buried 20–30 cm underground and extend 50 cm above ground. Stakes or bamboo poles support the barriers, and the corners are rounded to prevent escape. A 1-meter-high polyethylene mesh surrounds the pond for easy monitoring.
Fourth, pond cleaning and disinfection are necessary before stocking. Excess silt is removed, and after winter exposure, lime (70–100 kg per acre) is applied to disinfect and improve water quality. Sodium pentachlorophenol is strictly prohibited. Water is filtered through a 60-mesh nylon bag to prevent wild fish and eggs from entering.
Fifth, aquatic plants and snails are introduced to enhance the ecosystem. Plants like Vallisneria, Hydrilla, and floating peanuts provide shelter, improve water quality, and serve as natural feed. Snails help control plankton and organic matter. Aquatic plants cover about 30% of the pond area, and snails are stocked at 200–300 kg per acre before April.
Sixth, a "crab holding area" is established in the deep part of the pond. This area covers 1/3 to 1/5 of the total pond size and is used to raise crabs until they grow and the snails are ready for full stocking.
For seed stocking, locally bred crabs are preferred due to their higher survival rate and resistance. Stocking occurs between late November to December and early February to April, at temperatures of 4–10°C. Crabs are stocked at 500–800 per mu, with a density of 120–200 per kg.
Shrimp are introduced in mid-May, with yellow-green, healthy individuals of 4–6 cm in size. About 3 kg per mu are released, and manure and soybean meal are used to cultivate the water, providing food for both shrimp and crabs.
Carp species are also stocked to help regulate water quality and reduce blue-green algae. One-year-old carp and 30–60 fish per mu are added, with sizes ranging from 10–20 per kg.
Feeding management involves using natural food such as snails, aquatic plants, and small amounts of plant-based feed. In the early stages, fresh fish and snails are the main sources, while later, pellet feeds and vegetables are used. Feeding is done 1–2 times daily, with morning and evening portions adjusted accordingly.
Water quality management is critical. Maintaining clear, oxygen-rich water with a temperature between 26–30°C and transparency of 35–50 cm ensures optimal conditions. Regular water changes, lime application, and biological agents like EM bacteria help maintain a healthy environment.
Disease prevention focuses on ecological practices, including clean water, healthy stock, and proper feeding. If disease occurs, approved low-toxicity drugs are used according to Ministry guidelines.
By following these integrated techniques, farmers can achieve better yields, reduce costs, and promote a sustainable aquaculture system.