Effects of soy isoflavones on growth performance, antioxidant capacity, non-specific immunity and lipid metabolism of juvenile Chinese mitten crab, Eriocheir sinensis

Abstract

Soy isoflavones are phytoestrogens that provide protection against some hormonal disorders and regulate several physiological functions in animals. This study investigates the effects of soy isoflavones on body composition, antioxidant activity, non-specific immunity, and lipid metabolism in juvenile Chinese mitten crabs, Eriocheir sinensis. A total of 960 juvenile crabs (1.09 ± 0.01 g) were randomly assigned to 24 tanks (300L), with 40 crabs in each tank in four replicates. The crabs were fed diets (43.5% protein and 7% lipid) with six levels of soy isoflavones (0, 8.8, 15.8, 33.8, 66.8, and 137.0 mg/kg) at 4% BW/day for 56 days. The final biomass and biomass gain of crabs supplemented with 15.8 and 33.8 mg/kg soy isoflavones were significantly higher than those in the control group. The total lipid content in the whole-body and hepatopancreas of the crabs fed 15.8 and 33.8 mg/kg soy isoflavones was significantly lower than in the control group. Compared with the control group, soy isoflavones significantly enhanced the activities of superoxide dismutase, glutathione peroxidase and total antioxidant capacity in the hepatopancreas by 40%, 57% and 79%, respectively, and significantly decreased malondialdehyde content by 24%. The high dietary soy isoflavones levels increased total protein and hemocyanin contents in hemolymph, and alkaline phosphatase activity was also significantly enhanced. The triglyceride contents in the hepatopancreas and hemolymph were significantly lower in the soy isoflavones-supplemented group. Dietary soy isoflavones may reduce lipid accumulation in the hepatopancreas by repressing genes related to lipid synthesis and promoting the expression of lipid oxidation and transport genes. The broken-line model analysis of biomass gain against dietary soy isoflavones levels shows that the optimal supplemental level of soy isoflavones for juvenile crabs is approximately 26.66 mg/kg. Thus, this study suggests that dietary soy isoflavones supplementation can improve growth performance and health and reduce lipid accumulation in the hepatopancreas of juvenile crabs.