Rice field finishing is a crucial step in creating an optimal environment for raising crabs. The selected paddy fields should be easy to manage and suitable for feeding and fortification, ensuring that the crabs can escape from potential threats. Field ridges need to be raised and widened, typically reaching a height of 50-60 cm with a top width of 50-60 cm. In the central area, "well" or "tian" type ditches should be dug, with a standard depth of 30 cm and a width of 40-60 cm. A small sink of about 6 to 8 square meters and 60 cm deep should also be constructed to provide shelter for crabs and young crabs during autumn. Drainage ditches are installed in opposite corners of the field, preferably using pipes with double-layer nets at the inner end to prevent young crabs from escaping. A 40-day barrier is placed to keep out predators like frogs and voles. Anti-escape walls should be set up before introducing crabs. Two common methods include embedding a glass fiber fence on the inner side of the ridge, 60 cm high with 40 cm above ground, or using bamboo stakes as a framework to install a plastic sheet, 60 cm high, buried 10-15 cm deep and tilted inward at 30 degrees with semi-circular corners. Additionally, some hidden labor structures can be added in the field to reduce predation and improve survival rates.
Feed management is essential for the healthy growth of crabs. Early-stage feed includes fresh water grass, Fish gills, Shrimp stomachs, cooked pig blood, tofu, and other easily digestible foods. As crabs grow, the diet can be expanded to include snail meat, stewed meat, soybean residue, crushed rapeseed cake, soybean cake, cooked corn, wheat, pumpkin, and food waste from restaurants or slaughterhouses. During the early stages, food should be filtered with gauze and fed 3-4 times daily, with an amount of 30-50% of the total Crab biomass. Later, feeding once a day in the evening is recommended, as crabs are more active at night. The feeding rate is estimated at 5-8% of the total weight of the seedlings, and this may vary based on factors such as water quality, weather, temperature, and molting cycles. It's important to ensure that crabs are well-fed but not overfed.
Water quality management is key to maintaining a healthy environment. When releasing crabs into the rice fields, fresh water is introduced to a depth of 10 cm, gradually increasing as water temperature rises and crabs grow. The water level should stabilize between 15-20 cm. Freshwater should be exchanged weekly, with each change adding 5-10 cm of new water to keep the crabs lively and maintain high dissolved oxygen levels. Lime should be applied monthly at a rate of 20 kg per acre to make the water slightly alkaline, which helps in sterilization, disinfection, and calcium supplementation. Based on water quality, additional organic manure (100-130 kg/acre) or urea (5-7 kg/acre) can be used. If possible, maintaining a gentle flow in the rice field can stimulate appetite and increase shell production.
Disease prevention and water quality control are especially important when rice diseases occur. Predators such as waterflies and snakes can threaten young crabs, so they must be removed or eliminated. Mice, in particular, are a serious threat, as they can kill 20-30 juvenile crabs overnight. Effective measures include rodent control and manual capture. Aquatic plants should be soaked in lime water (20-30 g/m³) and regular disinfection with quicklime should be carried out. Efficient, low-toxicity, and low-residue pesticides should be applied in portions to minimize contamination. After pesticide application, water should be changed to ensure it is safe. Juvenile crabs are typically harvested before rice harvesting, usually in mid to late September.
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