Planting Grass and Introducing Snails in Crab Ponds: Good Results with Proper Measures

With the expansion of crab farming scale and the increase in intensive farming, the water quality of farming waters has deteriorated, the quality of river crabs has declined, and diseases have worsened, affecting the improvement of river crab farming benefits. In recent years, Dalong Township, Dafeng City, Jiangsu, has adopted the method of planting grass and introducing snails to farm river crabs, achieving a good result of 55 kg of crabs per 667 sq m. The practices are as follows.

1. Pond requirements. The water quality is required to be fresh, the pond water depth more than 1.5 m, the pond bottom flat, the silt less than 20 cm, and the area preferably 0.67-1.33 hectares. The inlet and outlet of the crab pond should be set diagonally, with high irrigation and low drainage. Calcium-plastic boards are used around the pond to prevent escape. A holding pond is set up at the deep-water corner of the pond (with a flat bottom, a holding pond 50-60 cm deep can be dug at the pond corner or side), with an area accounting for 5%-10% of the total pond area.

2. Clearing and preparing the pond. In December, the pond is dried and exposed to the sun, excess silt at the bottom is removed, the pond ridge is repaired, and 15 days before the crab seeds are put into the pond, 75 kg of quicklime per 667 sq m is used for dry clearing and disinfection of the pond.

3. Purchasing and stocking crab seeds. The purchased juvenile crabs are required to be uniform in size, with complete appendages, free from disease and injury, and sexually immature. Around the Spring Festival, 500-600 juvenile crabs of 100-200 crabs per jin are stocked per 667 sq m of pond. The juvenile crabs are first placed in the holding pond for temporary rearing, and water peanut is transplanted in the pond to provide habitat and shelter for the crabs. Before transplanting, the water peanut is disinfected with 20 g/cubic m lime water.

4. Aquatic grass cultivation. Around Qingming, tape grass is sown. 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, the pond water is controlled within 20 cm to promote early germination and tillering of the seeds, so as to meet the needs of river crab growth later. As the water temperature rises, the pond water level can be deepened to 60-80 cm, so that the aquatic grass grows longitudinally, becomes a place for river crabs to molt and hide, and can absorb excess nutrients, purify water quality, shade and cool down, and provide feed.

5. Snail introduction. Around Qingming, 150 kg-200 kg of live snails are introduced per 667 sq m, and the snails need to be disinfected before introduction. Benefits of introducing snails: (1) Snails feed on the leaves of aquatic plants and benthic algae, and 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 tape grass, 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 physical energy after overwintering. Therefore, in the early stage, feeding should mainly be comprehensive-nutrition pellet feed, appropriately matched with some animal feed, fed once every evening. By May, as the water temperature rises, river crabs enter a period of vigorous growth, and feed is given twice, mainly full-price river crab feed, with the feeding amount based on being eaten within 2 hours. In the high-temperature season from July to September, more plant-based feed should be given to help river crabs accumulate physical energy.