Key Technical Points for Planting Grass and Stocking Snails in Crab Culture Ponds
With the expansion of crab culture scale and the improvement of intensive farming levels, the water quality of aquaculture waters has deteriorated, the quality of river crabs has declined, and diseases have worsened, affecting the improvement of river crab culture benefits. In recent years, Dalong Township, Dafeng City, Jiangsu, has adopted the method of planting grass and stocking snails to culture river crabs, achieving a good result of 55 kg of crabs per 667 sq m. The methods are as follows.
1. Pond requirements. Water quality should be fresh, pond water depth should be over 1.5 m, the pond bottom should be flat, with silt of 20 cm or less, and an area of 0.67-1.33 hectares is preferable. The inlet and outlet of the crab culture pond should be arranged diagonally, implementing high irrigation and low drainage. Calcium-plastic boards are used around the pond for escape prevention. A temporary holding pond should be set up in a deep-water corner of the pond (with a flat pond bottom, a temporary holding pond 50-60 cm deep can be excavated at the pond corner or side), with an area accounting for 5%-10% of the total pond area.
2. Pond cleaning and preparation. In December, drain the pond and expose it to the sun, remove excess silt from the pond bottom, and repair the pond embankments. Fifteen days before stocking crab seedlings, use 75 kg of quicklime per 667 sq m for dry pond disinfection.
3. Crab seedling selection and stocking. The purchased juvenile crabs should be uniform in size, with intact appendages, free of disease and injury, and sexually immature. Around the Spring Festival, stock 500-600 juvenile crabs of 100-200 crabs per jin in each 667 sq m pond. The juvenile crabs should first be placed in the temporary holding pond, where water peanut is transplanted to provide habitat and concealment for the crabs. Before transplanting, the water peanut should be disinfected with 20 g/cubic m lime water.
4. Aquatic grass cultivation. Around Qingming, sow Vallisneria. Before sowing, soak for 12 hours and wash off the mucus on the seeds. When sowing, mix evenly with fine soil or fine sand and broadcast over the whole pond, sowing 50 g per 667 sq m. After the seeds are put into the pond, keep the pond water within 20 cm to promote early germination and tillering of the seeds, so as to meet the growth needs of river crabs later. As the water temperature rises, the pond water level can be deepened to 60-80 cm, allowing the aquatic grass to grow vertically, becoming a place for river crabs to molt and hide, and also absorbing excess nutrients, purifying water quality, providing shade and cooling, and supplying feed.
5. Snail stocking. Around Qingming, stock 150 kg-200 kg of live snails per 667 sq m. Before stocking, the snails need to be disinfected. Benefits of stocking snails: (1) Snails feed on the leaves of aquatic plants and benthic algae, which can purify water quality; (2) Snails reproduce relatively quickly and can be continuously supplied as river crab feed; (3) Snails have low cost and wide sources, and combined with planting Vallisneria, they can better control the pond water quality and provide a fresh living environment for river crabs.
6. Daily management. When juvenile crabs are stocked, the water temperature is relatively low, and the juvenile crabs have consumed energy after overwintering. Therefore, in the early stage, feeding should mainly be nutritionally complete pellet feed, appropriately paired with some animal-based feed, fed once every evening. By May, as the water temperature rises, river crabs enter a period of vigorous growth, and feed should be given twice, mainly with complete-formula river crab feed, with the feeding amount based on being consumed within 2 hours. In the high-temperature season from July to September, more plant-based feed should be given to help river crabs accumulate energy.