Effects of fructooligosaccharide on immune response, antioxidant capability and HSP70 and HSP90 expressions of blunt snout bream (Megalobrama amblycephala) under high ammonia stress

This study aimed to determine the effects of fructooligosaccharide (FOS) on immune response, antioxidant capability and HSP70 and HSP90 mRNA expressions of blunt snout bream (Megalobrama amblycephala) under high ammonia stress. A total of 360 fish were randomly distributed into three groups (each with four replicates) and were fed three levels of FOS (0, 0.4 and 0.8 %) for 8 weeks. After the feeding trial, 24 fish per tank were exposed to ammonia at 10 mg L-1. After stress, plasma cortisol and glucose levels of fish fed 0.4 % FOS were all significantly lower than that of the control group at 6 and 3 h, respectively. Plasma lysozyme and alternative complement pathway (ACH50) activities as well as nitrogen monoxide (NO) levels all increased significantly with the maximum levels being attained at 6, 6 and 3 h, respectively. Thereafter, these parameters all decreased significantly. In addition, fish fed 0.4 % FOS showed higher immune parameters under stress compared with that of control group. In addition, liver superoxide dismutase and catalase activities of fish fed 0.4 % FOS were both significantly higher than that of the control group before and after stress, while the opposite was true for malondialdehyde content. After stress, the expression of HSP70 and HSP90 of fish fed FOS was significantly higher than that of the control group at 6 and 12 h, respectively. After 12 h stress, the cumulative mortality of fish fed FOS was significantly lower than that of the control. The results indicated that the supplementation of 0.4 % FOS could increase the nonspecific immunity, antioxidant capacity and HSP70 and HSP90 expression of blunt snout bream and enhance its resistance to high ammonia stress.