In current crab farming practices, the integration of other fish species is typically managed alongside large crabs at a density of about 500 per acre. To maximize water resource utilization, 10 to 30 individuals of each species can be introduced per acre after the initial release of crabs. This includes approximately 5 to 7 kilograms of heterotrophic silver carp and 2 to 3 kilograms of green shrimp. Additionally, from May to early June, 15 to 30 young carp (5 to 7 cm in size) can be added per acre. The reason for this practice is that squid serves as a primary food source for bottom-dwelling fish and shrimp. Introducing squid helps control wild crabs and shrimp that compete with farmed crabs for oxygen, space, and food.
Before the first molt of crabs, careful management of oyster shells is essential. Early-stage breeding should focus on shallow water, light exposure, and increased water temperature to encourage early feeding. Small trash fish or high-quality pellets should be provided to ensure smooth shell development. Avoid applying medications or fertilizers during critical molting periods, and monitor the molting cycle closely to predict the next peak. Disinfection of the crab pond should occur one week before the molting peak, and feed should be supplemented with around 1% of calcium dihydrogen phosphate, fructooligosaccharides, vitamin C, and Sanhuangsan. During the molting period, reduce feeding and maintain a calm environment to minimize stress.
Controlling algae growth in the crab pond is crucial. In the early stages, maintaining a certain level of water turbidity with a depth of 30 to 40 cm helps weaken the light needed for algae growth. Before and after the Qingming Festival, snails should be introduced to replace algae. When algae start to grow, copper sulfate can be used to control it, but care must be taken to avoid damaging aquatic plants. After treatment, fresh water should be added the next day. For smaller ponds, manual removal of algae is recommended during the growing season.
Maintaining an appropriate level of aquatic plants not only provides natural feed for crabs but also helps regulate water temperature, offers shelter, and absorbs excess nitrogen, phosphorus, and heavy metals, thus preventing eutrophication and water pollution. Crab ponds should have a mix of submerged plants like Elodea and Vallisneria, floating plants such as water spinach and water peanuts, and a small amount of emergent plants like reeds. The coverage of aquatic plants should be kept between 60% and 70% during the crab's growth phase to ensure a balanced ecosystem.
Introducing snails into the pond provides a natural protein source for crabs and helps clean the pond bottom. The first introduction of live snails usually occurs before the Qingming Festival, with 15 to 200 kg per acre, allowing them time to adapt and produce young snails for early feeding. From June to August, another batch of 150 to 250 kg per acre is released. This two-phase approach prevents excessive waste, which could lead to poor water quality and excessive algae growth, both of which negatively impact crab development.
Feeding should be adjusted according to the nutritional needs of crabs at different growth stages. A balanced diet should include fine particles, green vegetables, animal-based ingredients, and vegetarian components. The ratio of animal to plant-based feed should be 60:40 before mid-June, 45:55 from late June to mid-August, and 65:35 from mid-August to mid-October. Enzyme preparations should be added to compound feeds to enhance digestion. Feeding should be done primarily in the evening to ensure crabs consume the feed promptly, reducing waste and improving water quality and disease prevention.
To maintain sufficient dissolved oxygen, the pond should be kept at an appropriate depth, with micro-tube aeration systems installed at the bottom. Regular water changes are important, especially from June to September, when more frequent water exchanges should be carried out. On sunny afternoons between 1 and 4 PM, or early morning, fresh water should be added to create a gentle flow, keeping the water clean. During rainy or hot weather, chemical oxygenation agents like granular oxygen should be used in the evening to supplement aeration.
Water quality monitoring is essential. Transparency should be maintained at 30–40 cm before the end of May, then increased to over 50 cm. From July to August, water should be changed every 7–10 days, with a 30 cm change each time. From September to October, weekly water changes of 1/3 of the total volume are recommended. pH levels should also be regularly checked and adjusted as needed.
Biological agents such as EM bacteria and photosynthetic bacteria can be used in the crab pond from July to September, applied four times. These should be used in the morning, after starting the aerator, and followed by particulate oxygen boosters 1–2 hours later. It is important to avoid using these agents together with disinfectants or antibiotics, as they may interfere with their effectiveness.
Disease prevention is key. From May to June, disinfectants like chloral hydrate can be used at a rate of 0.3 grams per cubic meter. From July to September, crabs can be fed EM microbial preparations for three consecutive days. Before releasing crabs in October to November, ciliate-killing drugs can be applied 20–25 days in advance. At the same time, measures should be taken to prevent predators such as frogs, cockroaches, mice, crawfish, and birds from attacking the crabs.
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