Hairy crabs prefer freshwater environments with plenty of sunlight and abundant aquatic vegetation. They typically live in the mud along riverbanks and irrigation channels, feeding on small fish, shrimp, snails, crickets, insects, and animal remains. When the temperature drops below 10°C, they become less active and eat less, often burrowing into the soil for winter. Each year, during autumn and winter, mature crabs migrate to spawn.
**Field Construction**
To create an ideal environment for crab farming, choose a quiet area with a steady water supply, good water quality, and no industrial pollution. The site should be easy to access, flood-resistant, and have strong water retention capabilities. The paddy field should be at least 1.5 meters wide, with an area ranging from small to around 10 mu (approximately 0.67 hectares). Dig ditches about 2-3 meters inside the ridges, 1-2 meters wide and 1 meter deep, with a slope of 1:1.2. These ditches can be shaped like "ten" or "well" patterns and connected to an outer ring ditch. Aquatic plants such as water spinach are planted on the ditches, covering 30%-50% of the surface to provide shelter and food for the crabs.
A temporary holding pool, 1.5 meters deep and occupying 5% of the total field area, is built at one end. The overall construction accounts for 15%-20% of the paddy land. Inlet and outlet openings are placed diagonally, with mesh screens installed to prevent escape. Fences made of smooth, durable materials like calcium plastic sheets or plastic films are set up around the field, extending 40-50 cm above ground level and 10 cm underground. These are secured with wooden stakes or strong ropes to ensure no gaps or folds.
**Crab Stocking**
Healthy crabs with full limbs, strong bodies, and consistent size are selected, with a minimum of 60-100 per kilogram. Crabs are usually purchased before the Qingming Festival and first raised in the holding pool. If transported over long distances, they should be soaked in water for 3 minutes, then allowed to dry for 10 minutes, and repeated several times to help them recover. After they turn green, they are disinfected with formalin at 50-100 mg/L before being introduced into the fields. The stocking density is around 15-20 kg per mu.
**Feeding Management**
For rice cultivation, high-yield varieties with strong disease resistance and hard stalks are preferred. Planting density is increased at the edges to maximize yield. A single application of base fertilizer is used, and top-dressing is generally avoided. Before transplanting, seedlings are sprayed with pesticides 1-2 days in advance. If necessary, insecticides, disinfectants, and jinggangmycin can be used, but care must be taken to minimize exposure to crabs.
Water quality is crucial for crabs, requiring fresh, slightly alkaline or neutral water with dissolved oxygen levels above 5 mg/L. Water is changed every 3-5 days, replacing about 10 cm of water each time. Adjustments are made based on crab size, water temperature, and weather conditions.
In addition to naturally growing aquatic plants and benthic organisms, artificial feeds such as small fish, snails, clams, fish meal, blood meal, and plant-based feeds like duckweed, algae, and soybean cake are provided. Feeding methods vary: initially, protein-rich foods like pig blood and snails are given, followed by more plant-based feeds mid-cycle, and finally, more animal-based feeds to promote growth. Feed is given daily at 5%-10% of body weight, adjusted according to weather and activity. Feeding occurs in the late afternoon to encourage nighttime feeding.
Regular inspections in the morning and evening help monitor crab health, feeding behavior, and the integrity of anti-escape measures.
**Disease Prevention**
Sterilization is done every two weeks, and feed is supplemented with chitin, additives, and antibiotics to support growth and prevent disease. Measures are also taken to eliminate predators such as rats, frogs, snakes, and birds.
**Harvesting**
After rice harvest, crabs are caught at night using light traps, which reduce mortality. High-quality crabs are those with two or more legs, golden claws, yellow hair, green shells, white bellies, firm meat, and minimal water content. They should look clean and have a pleasant appearance.
**Important Note**
Crab farming in rice fields offers significant economic benefits, but it requires advanced technical knowledge. Farmers should thoroughly understand and master aquaculture techniques before starting. If needed, they should consult local fisheries authorities for guidance.
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