Success Stories In Asian Aquaculture - Library - Network of ...

28 M. Weiminmany parts of China, driven by high market value and better adaptability to the ricefield environment. However, successful rice-crustacean culture requires differentmodifications to the rice field, particularly installation of shelter and more carefulmanagement practices, because crustacean are more sensitive to many chemicalsand pesticides used in rice cultivation. Economic returns from rice-crustacean cultureare much higher than rice–finfish culture. Normal net income usually rangesbetween $2,500 and $4,000 per hectare.Red swamp crawfish-rice culture is a rapidly developing practice in the centralpart of China. Apart from the normal fish trenches and pits inside the rice field,vertical surrounding fence (30 cm deep into soil and 30 cm high above soil) establishedwith bricks, rigid plastic sheets, or other materials is required for preventionof escape of crawfish. Aquatic plants are needed to be planted inside the trenchesand pits to provide shelter for postmolting protection, which usually covers about30% of the trench and pit area. Some 300–750 kg/ha of berried crawfish or150,000–225,000 individuals/ha of juvenile crawfish (2–3 cm) are stocked.Supplementary feeding is required especially when stocking density is high.Crawfish is typically omnivorous. By-products of grain processing and oil extraction,animal feed such as snail, trash fish, earthworm, poultry entrails, and floatingaquatic plants are all well accepted. The feeding rate is dependent on the feeding ofcrawfish, which should be monitored daily. It often ranges 3–5% of the body weightand is subject to adjustment based on the water quality and weather conditions.Feeding is much reduced when water quality is somewhat poor, or continuous rainyand cloudy weather is encountered. The stocking is usually carried out in November(for berried crawfish) or March (for juvenile). Harvesting is through both selectiveharvesting (trap set inside the trench and pit) and total harvesting by draining thewater. The average yield is 6,000–7,500 kg/ha (Plate 2.2 ) .Plate 2.2 Rice-river crab culture in Nantong city, China (Miao 2002)