Effects of different stocking densities on growth performance, nutritional quality and economic benefit of juvenile female Chinese mitten crab (Eriocheir sinensis) in rice-crab culture systems

This study assessed the effects of stocking density on the growth performance, nutritional quality, and economic yield of female Chinese mitten crab (Eriocheir sinensis) in rice-crab culture system. For this purpose, juveniles (6.74 ± 0.25 g) of crabs were stocked to the rice field at five stocking densities viz., 0.2 inds./m², 0.3 inds./m², 0.4 inds./m², 0.5 inds./m² and 0.6 inds./m² with a control rice field without crab each with three replications. After 72 days of culture, mean growth of crab was 63.91 ± 2.09 g, 61.62 ± 0.84 g, 61.24 ± 3.98 g, 55.59 ± 1.72 g and 55.18 ± 0.69 g at the mentioned stocking densities, respectively indicating decrease in growth with the increase in stocking density. Hepatosomatic index (HSI) of crab was also decreased with the increase in stocking density. But highest gonadosomatic index (GSI) was recorded at 0.4 inds./m² density. At the same density, crude fat level of hepatopancreas and crude protein level of ovary of crabs were also highest. Amino acid composition was balanced and essential amino acid score was highest in the muscle and ovary of crabs at this density. Polyunsaturated fatty acids (PUFA) and n-3 PUFA of hepatopancreas, and docosahexaenoic acid (DHA), PUFA, n-6 PUFA and DHA of ovary were significantly (P < 0.05) higher in crabs at 0.4 inds./m² in comparison to other stocking densities. At this density, crabs showed more obvious promotion effect on the relative expression of EcR, RXR and IGF2 genes in muscle and EcR and IGF2 genes in hepatopancreas compared with other stocking densities. In comparison to control, rice crab culture systems can bring better economic benefits and reasonable stocking density can effectively increase rice yield. Net profit was highest at 0.4 inds./m² density followed by 0.5 inds./m² density with no significant difference in profit between these two densities. However, based on the growth performance, nutritional value and profitability, stocking densities of 0.4 inds./m² of female Chinese mitten crab, E. sinensis can be considered optimum for rearing in the rice field.