Crab incubation technique

At present, most crab farmers still rely on the traditional rapid cultivation method, which involves early seedling production within the same year. This approach often results in crabs that are small in size, of poor quality, and difficult to sell at a competitive price. To address these issues, the author proposes the concept of “climbing crabs and raising them slowly.” Through practical implementation, it was found that controlling the growth rate is crucial for producing high-quality crabs. When crabs grow slowly, reaching a size of 1000 to 1500 per kilogram, they can develop better characteristics. On the other hand, if they grow too quickly—reaching 30 to 50 per kilogram—they may experience early sexual maturity, which negatively affects their quality. The standard for quality crabs includes: 1) uniform size, ideally between 120 to 300 per kilogram; 2) second-year crabs, with females around 125 grams and males about 150 grams; 3) a precocious puberty ratio not exceeding 10%; 4) a survival rate of approximately 50%; 5) strong, active crabs without injuries or parasites such as crab lice or polyhelminthes; and 6) authentic Yangtze River Chinese mitten crabs. To achieve this, the following technical points are recommended: 1. **Pond Conditions**: The pond should be between 667 and 1334 square meters (1 to 2 mu), with good water supply and drainage systems. Water plants should be maintained at 40% to 60% of the pond area, with additional plants like water peanuts or bitter herbs added if needed. 2. **Anti-Escape Facilities**: Juvenile crabs are highly active and phototactic, so inlet and outlet pipes must be covered with fine mesh. A 60-cm calcium plastic board should be installed around the pond, angled at 5 degrees to prevent escape. 3. **Seedling Selection and Transportation**: Seedlings should be purchased in mid-May. High-quality seedlings can be selected using the "see two questions and three investigations" method. Look for crabs with complete limbs, uniform size, and active behavior. Check the origin and desalination time, and investigate nursery records, parent crab conditions, and medication use. During transport, place seedlings dry in boxes, with smaller crabs at the bottom and larger ones on top, holding 0.5 to 0.75 kg per box. Proper handling ensures no damage after 24 hours. 4. **Rearing Young Crabs**: To improve survival rates, young crabs are first raised in a middle stage before being moved to final pools. This allows for better growth, with an estimated 20,000 to 40,000 crabs per 667 square meters. This method increases survival by about 10% compared to direct stocking. 5. **Preventing Precocious Puberty and Management**: Preventing early sexual maturity is key. This involves: 1) controlling stocking density (20,000–40,000 per 667 m²); 2) monitoring water quality, changing it every 15 days and applying lime when necessary; 3) increasing water depth in summer to reduce accumulated temperature; 4) feeding appropriately—starting with 20% of body weight and gradually reducing to 8–10%, while increasing plant-based feed; 5) winter management, including raising water levels and adding manure; 6) disease prevention, focusing on hydromycosis, ciliate disease, and limb rot; and 7) proper timing for harvesting, using traps and dry ponds before and after the Spring Festival. With proper techniques and care, farmers can expect to raise about 10,000 crabs per 667 m², with high-yield farms reaching up to 15,000. The economic benefits are significant, making this method a viable and profitable alternative to traditional practices.

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