Hairy crabs thrive in environments with fresh water, ample sunlight, and a rich supply of aquatic vegetation. They typically reside in muddy areas along riverbanks and irrigation channels, feeding on small fish, shrimp, snails, crickets, insects, and animal remains. When temperatures drop below 10°C, the crabs become inactive and reduce their food intake or stop eating altogether. Each autumn and winter, mature crabs migrate to reproduce, carrying their gonads to suitable breeding grounds.
Field Setup
To create an ideal habitat for crabs, choose a quiet, well-watered area with clean, unpolluted water. The site should be flood-resistant, have good water retention, and be easy to access. The paddy field should be at least 1.5 meters wide, with an area ranging from small to about 10 mu (approx. 6.67 acres). Dig ditches approximately 2-3 meters from the ridge, 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, connecting to an outer ring ditch. The ditch surfaces are used for planting water spinach or aquatic plants, covering 30%-50% of the area. A temporary holding pool, 1.5 meters deep and occupying 5% of the total area, is built at one end of the field. Overall, the field infrastructure accounts for 15%-20% of the paddy area. Inlet and outlet openings are placed diagonally and covered with fine mesh nets to prevent escape. Water plants are also planted in the ditches and pools to provide natural food and shelter.
The perimeter is enclosed with smooth, durable materials such as calcium plastic boards or plastic sheets, extending 40-50 cm above ground level and 10 cm below the soil surface. The outer side is secured with wooden stakes or strong ropes to prevent escape. The anti-escape barriers must be seamless and free of gaps.
Crab Stocking
Only healthy, active crabs with complete limbs and no signs of disease should be selected. The size should be at least 60-100 per kilogram. Crabs are usually purchased before the Qingming Festival, often sourced from coastal regions. Before stocking, they are first acclimated in a holding pool. If transported over long distances, the crabs should be soaked in water for 3 minutes, then allowed to rest for 10 minutes, repeating this process several times to help them recover. Once they return to a green color, they are disinfected with formalin at 50-100 mg/L for a few minutes before being released into the fields. Stocking density is around 15-20 kg per mu.
Feeding Management
Rice varieties with high yield, strong resistance, and sturdy stalks are preferred. Planting is done with wider rows and increased density near the field edges to maximize rice yield. A single application of base fertilizer is used before transplanting, and top-dressing is generally avoided. Before transplanting, the seedlings are sprayed with pesticides 1-2 days in advance. If necessary, insecticides, disinfectants, or Jinggangmycin can be used during growth, but always with care. Prior to spraying, the field is flooded to minimize runoff and increase absorption by the plants. Avoid using harmful chemicals that could affect the crabs.
Crabs require clean, well-oxygenated water, ideally slightly alkaline or neutral, with dissolved oxygen levels above 5 mg/L. Low oxygen levels can cause feeding to stop, and even death. Similarly, low pH can hinder molting and affect growth. Water is changed every 3-5 days, replacing about 10 cm of water each time. Adjustments are made based on crab size, temperature, and weather conditions.
In addition to naturally growing aquatic plants and benthic organisms, supplementary feed is provided throughout the breeding cycle. Animal-based feeds include small fish, shrimp, silkworm pupae, clams, snail meat, fish meal, blood meal, and slaughterhouse waste. Plant-based feeds consist of aquatic plants, duckweed, algae, melon scraps, soybean cake, bran, and rice bran. Artificial compound feed can also be used.
Initially, crabs are fed animal-based foods like fish gizzards, pig blood, silkworm pupae, snails, and quail meat. As they grow, plant-based feeds such as pumpkin, wheat, and bean cake become more prominent. In later stages, the diet shifts back to animal-based feed to promote weight gain. Daily feeding amounts range from 5%-10%, adjusted based on weather, water temperature, and crab activity. Feeding occurs between 4-5 PM to encourage nighttime feeding. Food is placed around the ditches for easy access.
Regular inspections are conducted in the morning and evening to monitor crab behavior, check feeding habits, and ensure anti-escape measures are intact. Early detection of issues allows for prompt action.
Disease Prevention
Preventive measures include sterilizing the environment every two weeks and adding supplements like chitin or antibiotics to the feed to support growth and prevent illness. Effective control methods are implemented to eliminate pests such as rats, frogs, snakes, birds, and other potential threats.
Harvesting
After the rice harvest, crabs are collected. Releasing water at night improves the effectiveness of light trapping, reducing crab mortality. High-quality crabs have strong claws, yellow hair, green shells, white bellies, tender meat, and a fresh, clean appearance with minimal odor.
[Special Note]
Crab farming in rice fields offers significant economic benefits, but it requires careful technical management. Before starting, farmers should thoroughly understand and master aquaculture techniques. It is advisable to consult local fisheries departments for guidance if needed.
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