The effect of stocking density of Chinese mitten crab Eriocheir sinensis on rice and crab seed yields in rice-crab culture systems

Normally Chinese mitten crab Eriocheir sinensis were cultured for 2 years, 1 year is cultured from crab larvae to seeds or button sized crab in ponds, tanks or rice fields, the another year is cultured from seeds to market size in ponds, reservoirs or other waters. The present study was conducted to determine the effect of stocking density (0, 3.75, 15, 30 and 60 inds. per m(2), respectively) of Chinese mitten crab larvae on rice and crab seed yields in rice-crab culture systems using land-based enclosures (4 m x 7 m, with three replicates for each stocking density) at the Panjin Guanghe Fisheries Co. Ltd, in the Liaohe Delta, China. Zoobenthos biomass, production of crab and rice paddy, and economical profit among the treatments were determined. The experiment showed that zoobenthos biomass in rice-crab culture systems was relatively variant and not significantly correlated to these stocking density. The biomass of aquatic plant declined significantly with increasing stocking density. Specific growth rates (SGR) and survival rates of the crab were significantly higher at the lower stocking density (P<0.05); in addition, the ratio of precocious crab and total crab significantly increased with the stocking density increasing (P<0.05); There were not significant effect of presence of crab on yields of rice straw and rice paddy (P>0.05). Net crab yield and net profit were the highest at the 15 treatment (P<0.05), however, the net profits among 3.75, 15 and 30 treatments did not show significant difference (P>0.05) economically. Based on the observations above, a stocking density of 3.75 to 30 inds. per m2 was considered reasonable in rice-crab culture system. (C) 2007 Elsevier B.V. All rights reserved.