The crab is a cold-blooded aquatic creature, and it thrives best in water temperatures ranging from 20°C to 28°C. This temperature range is ideal for its growth and development. During this period, it's crucial to carry out all feeding and management tasks efficiently, as this directly impacts the yield, size, quality, and economic returns of crab farming. Based on years of practical experience, here are the key technical points to consider:
Currently, many farmers raise large crabs at a density of about 500 per acre. To make better use of the water body, it's recommended to introduce other fish species such as silver carp (5–7 kg per mu) and green prawns (2–3 kg per mu) after placing the crabs. Additionally, from late May to early June, it's beneficial to intensively cultivate small carp (15–30 per acre, 5–7 cm in size). These carp feed mainly on small fish and shrimp, which helps control wild fish and shrimp in the crab pond that might compete with crabs for oxygen and space.
Shell management is a critical aspect of crab farming. Before the first molt, shallow water levels should be maintained to increase light exposure and water temperature, encouraging crabs to start feeding early on trash fish or high-quality pellets. This improves survival rates and ensures smooth molting. When applying medicine or fertilizers outside the molting period, it’s important to avoid overlapping with the molting cycle. Monitoring the molting patterns and predicting the next peak allows for timely disinfection and proper feed supplementation, such as adding 1% calcium dihydrogen phosphate, fructooligosaccharides, vitamin C, and Sanhuangsan to the feed.
Controlling algae in the crab pond is also essential. In the early stages, using appropriate fertilization techniques can maintain a certain level of water turbidity (30–40 cm), which inhibits moss growth. After Qingming Festival, two rounds of casting are recommended. If moss appears, copper sulfate and moss nets can be used, but care must be taken to avoid damaging aquatic plants. For smaller ponds, manual removal is often more effective.
Maintaining a balanced presence of aquatic plants is vital. Submerged plants like Elodea and Vallisneria, along with floating plants like water spinach and water peanuts, help provide natural food, regulate water temperature, and absorb pollutants. The coverage of water grass should be kept between 60% and 70%, and adjustments should be made if it becomes too sparse or dense.
Introducing snails into the pond is an effective way to improve the environment. Snails not only serve as a protein source for crabs but also help clean the pond bottom. A first release of 150–200 kg per acre before the Qingming Festival allows snails to adapt early, while a second round in June to August (150–250 kg per acre) prevents overstocking and reduces the risk of algae overgrowth.
Feeding strategies should be adjusted based on the nutritional needs of crabs at different stages. From early spring to mid-June, animal-based feeds should dominate (60:40 ratio), gradually shifting to a higher proportion of plant-based feeds during summer. Feeding should be reduced during hot seasons to prevent overeating, and enzyme preparations should be added to enhance digestion. Feeding should primarily occur in the evening to ensure efficient consumption and reduce waste.
Oxygen levels in the water are crucial, especially since crabs are benthic animals. Installing micro-aeration systems and maintaining proper water depth can improve dissolved oxygen levels. Water changes should be increased from June to September, and chemical oxygenation agents like granular oxygen should be used when necessary, especially during rainy or high-temperature periods.
Water clarity should be maintained at 30–40 cm by the end of May, increasing to over 50 cm in summer. Regular water changes—every 7–10 days in July–August and weekly in September–October—are essential for keeping the water fresh. During the rainy season, pH levels should be monitored, and lime should be applied promptly. After six months, additional minerals should be provided through feed.
Biological agents like EM bacteria and photosynthetic bacteria should be used from July to September. They should be applied on sunny mornings with aerobic conditions, followed by the use of particle oxygenation agents. These should not be used simultaneously with disinfectants or antibiotics.
Disease prevention focuses on ecological breeding practices. Regular disinfection, such as using bromochlorohydantoin at 0.3 g/m³, and oral administration of EM preparations can help control pathogens. Preventive measures against predators like snakes, frogs, rats, and birds are also important to ensure a safe environment for crabs.
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