The crab has gained widespread popularity among both domestic and international consumers due to its rich nutritional value and delicious meat. Currently, river crabs have become one of the main species in aquaculture across various regions. The crab farming industry has evolved from a focus on quantity—producing "large crabs"—to raising high-quality, eco-friendly crabs that emphasize both quality and efficiency. As the industry develops, small-sized and low-quality crabs are increasingly being rejected by consumers. Large crabs not only sell more easily but also offer a significant price advantage. The market price for large crabs can be 3-4 times higher than that of smaller ones, with prices ranging from 120-160 yuan per kilogram for crabs over 150g, while those under 75g may only fetch 30-40 yuan per kilogram. However, the challenge remains how to produce large crabs in a pollution-free way. A large crab is typically defined as one weighing 150g or more, characterized by a "green back, white belly, yellow hair, and golden claws." Based on years of practical experience, the key techniques for raising large river crabs include:
First, selecting high-quality breeds and releasing healthy crabs. High-quality crabs are essential for successful breeding. It's recommended to choose crabs from self-cultivated or local Nagasaki water systems that are robust, disease-free, and have uniform size. Avoid using young crabs of unknown origin. This is the most critical factor in improving survival rates. When selecting high-quality crabs, you can assess them based on their appearance, body shape, leg structure, and prefrontal teeth. "Small dumpling crabs" refer to first-instar crabs weighing 10-35g, which may mature, stop growing, and die quickly. Check for signs of incomplete legs, activity levels, and presence of parasites on the body to ensure you're selecting healthy specimens.
Second, planting aquatic plants to create a favorable ecological environment. As the saying goes, "Crab size depends on aquatic plants." Aquatic plants serve as natural feed for crabs, provide shelter, reduce predation, and help maintain water quality through photosynthesis. They also increase dissolved oxygen and absorb organic matter, preventing eutrophication. Additionally, they offer shade during hot weather, which helps crabs grow better. It’s best to plant a mix of submerged, emergent, and floating plants like Vallisneria, reeds, and duckweed. The coverage should be around 50-60% of the pond surface. During peak feeding seasons (July-August), ensure sufficient plant availability. If not enough, supplement with additional plants, but avoid overgrowth, which can lead to poor water circulation and disease outbreaks.
Third, controlling stocking density and practicing rational polyculture. Stocking density depends on crab size, feeding conditions, market demand, and management practices. A two-year breeding cycle is common, with seedlings purchased in late May or early June and grown in ponds until the end of the year. In the following spring, they are transferred to another pond. Typically, 100-200 crabs per kilogram, or 300-500 per acre, is a good range. Avoid mixing with herbivorous or carnivorous fish, but some filter-feeding species like eels or shrimp can be added to control plankton and improve water quality. The number of supplementary species should be limited to prevent overcrowding.
Fourth, introducing snails to meet the nutritional needs of crabs. Snails, especially apple snails, are an excellent live food source for crabs. They are benthic, easy to raise, and help purify water. Planting 150-250 kg of snails per mu in the pond ensures a continuous supply of protein-rich bait. Apple snails are particularly beneficial because they grow quickly, have high meat content, and contribute to overall crab health and growth.
Fifth, managing water quality to promote healthy crab development. Crabs require clean, well-oxygenated water with a pH between 7-8.5 and transparency of 30-40 cm. Regular water changes and the use of lime or microbial preparations like EM bacteria can help maintain optimal conditions. Water should be refreshed every 10-15 days, with more frequent changes during hot seasons.
Sixth, implementing effective disease prevention measures. With the expansion of crab farming, diseases such as ciliate infestations and shaking disease have become more prevalent. Prevention is key, and early detection and treatment are essential. Using microbial products, lime, and alternating antibiotics can help control outbreaks and reduce resistance. For shaking disease, specific treatments like enemy-killing agents are recommended.
By following these six key techniques, farmers can successfully raise high-quality, large-sized crabs that meet market demands and ensure sustainable production.
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