The crab is a cold-blooded aquatic creature, and its optimal growth temperature lies between 20°C and 28°C. During this period, it's essential to carry out all feeding and management activities efficiently, as this phase directly impacts the yield, size, quality, and economic returns of crab farming. Based on years of experience, here are the key technical points for successful crab cultivation:
Currently, the practice of raising other fish species alongside crabs follows the method of stocking large crabs at about 500 per acre. To make better use of water space, it’s recommended to allocate 10 to 30 mu of additional area after placing crabs. In that space, you can introduce 5 to 7 kg of heterotrophic silver crucian carp and 2 to 3 kg of green prawns per mu. Additionally, from late May to early June, you can intensively cultivate 15 to 30 small carp per acre. These carp primarily feed on small trash fish and shrimp, helping control wild fish and shrimp populations in crab ponds, which reduces competition for oxygen and space.
Shell management is crucial. Before the first molt, shallow water levels should be maintained to enhance light exposure and increase water temperature, encouraging early feeding with small trash fish or high-quality pellets. This ensures smooth molting and improves survival rates. Avoid applying medication or fertilizers during critical shell periods. Monitor the molting cycle and predict the next peak. Disinfect the pond one week before the peak by adding 1% locust, calcium dihydrogen phosphate, fructooligosaccharides, vitamin C, and Sanhuangsan to the feed. Reduce feeding during the molting peak and keep the environment quiet.
Moss control is also important. In the early stages, apply fertilizer to maintain a certain level of water clarity (30–40 cm). Use copper sulfate and moss nets when necessary, but be cautious of their impact on aquatic plants. After treatment, add fresh water promptly. For smaller ponds, manual removal is preferred during the growing season.
Maintaining moderate aquatic plants not only provides natural food for crabs but also helps regulate water temperature, offers shelter, absorbs pollutants, and prevents eutrophication. A mix of submerged (e.g., Elodea, Vallisneria), floating (e.g., water spinach, water peanuts), and emergent plants (e.g., reeds) should be used. Keep the coverage at 60–70% and adjust density as needed.
Introducing snails regularly enhances the protein content of the diet and cleans the pond bottom. Release 150–200 kg of live snails per acre before Qingming to help them adapt early. Add another 150–250 kg from June to August to avoid overloading the pond with nutrients and reduce algae growth.
Feed rations should be adjusted based on the nutritional needs of crabs. The ratio of animal to plant-based feed changes throughout the year: 60:40 before mid-June, 45:55 from late June to mid-August, and 65:35 from late August to October. Reduce feeding during hot and rainy seasons to prevent overeating. Use enzyme preparations in formulated feed to improve digestion. Feed mainly in the evening to ensure efficient consumption and minimize waste.
Oxygen levels in the pond must be maintained, especially since crabs are benthic creatures. Install micro-aeration systems if possible, and gradually add new water during early stages. Increase water exchange from June to September, especially in sunny afternoons. During rainy or hot weather, supplement with oxygen agents like granular oxygen.
Water transparency should be maintained at 30–40 cm by late May, then increased to over 50 cm in summer. Change water every 7–10 days from July to August, and weekly from September to October. Monitor pH levels, especially during the rainy season, and apply lime when needed. After six months, adjust mineral content in the water and supplement through feed.
Biological agents like EM bacteria and photosynthetic bacteria should be used from July to September. Apply them on sunny mornings, and follow up with oxygenation agents within two hours. Avoid using these alongside disinfectants or antibiotics.
Disease prevention focuses on ecological breeding and proper drug use. From late April to early May, treat ciliates with netting or shellfish nets before molting. Use bromochlorohydantoin at 0.3 g/m³ from May to June. From July to September, administer EM preparations orally. In October to November, prepare for harvest by using ciliate-killing drugs. Also, protect against predators such as snakes, frogs, rats, and birds.
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