1. **Rice Field Preparation**. When selecting paddy fields for Crab farming, it's important to choose areas that are easy to manage and provide good access for feeding and fortification. The field ridges should be raised and widened to prevent crabs from escaping. Typically, the ridge height should be 50-60 cm with a top width of 50-60 cm. A "well" or "tian" type ditch should be dug in the center of the field, with a standard depth of 30 cm and a width of 40-60 cm. Additionally, a small pit measuring 6-8 m² and about 60 cm deep should be created to provide shelter for crabs during their early stages and in autumn. Drainage ditches should be placed in opposite corners of the field, preferably using pipes. The inner end of the water pipe should be fitted with a double-layer net to prevent young crabs from escaping and to keep out predators like frogs and voles. Anti-escape walls should be installed before introducing crabs. Two common methods include embedding a fiberglass fence on the inner side of the ridge, 60 cm high with 40 cm above ground, or using bamboo stakes and plastic film to create a sloped barrier tilted inward at 30 degrees. Some farmers also install hidden traps in the field to reduce predation and improve survival rates.
2. **Feeding Management**. Early-stage river crabs are typically fed with fresh water grass, Fish gills, Shrimp stomachs, cooked pig blood, tofu, and other similar foods. As they grow, the diet can be expanded to include snail meat, cooked pork, soybean residue, crushed rapeseed cake, soybean cake, cooked corn, wheat, pumpkin, and food scraps from restaurants or slaughterhouses. During the early feeding phase, use a gauze filter and feed 3-4 times daily, with an amount equal to 30%-50% of the total weight of the crabs. Later, feed once a day in the evening, as crabs are more active at night. The feeding rate is usually around 5%-8% of the total weight of the seedlings, but this may vary depending on water quality, weather, temperature, and molting cycles. Ensure that crabs are well-fed but not overfed to maintain optimal health.
3. **Water Quality Management**. Freshwater should be introduced into the paddy field when crabs are first released, with a water depth of about 10 cm. As the water temperature rises and crabs grow, the water level should gradually increase. The ideal water depth is 15-20 cm. Water should be changed weekly, with each change involving 5-10 cm of fresh water to keep the environment clean and oxygen-rich. Lime should be applied monthly at a rate of 20 kg per acre to maintain slightly alkaline water conditions, which helps with disinfection and calcium supplementation. Depending on water quality, additional organic manure (100-130 kg per acre) or urea (5-7 kg per acre) can be added. If possible, maintaining a slow water flow in the paddy field can stimulate crab appetite and promote shell development.
4. **Disease Prevention and Control**. Young crabs are vulnerable to predators such as waterflies, snakes, and especially mice, which can destroy up to 20-30 crabs overnight. Effective control methods include rodent trapping, manual removal, and regular application of lime water to submerged aquatic plants. Quicklime should be used periodically to disinfect the water. When rice diseases occur, attention must be given to both disease prevention and water quality management. It's essential to use efficient, low-toxicity, and low-residue pesticides, applying them in small quantities to minimize contamination. After pesticide application, water should be changed to ensure it remains safe. Juvenile crabs are usually harvested before rice harvesting, typically between mid to late September.
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