Dietary supplementation of microbial floc heightens growth and improves digestive, immune, antioxidant enzymes activity and ammonia resistance in Opsariichthys kaopingensi s

Abstract

The present study was conducted to evaluate the effects of dietary supplementation of microbial floc on growth, digestive and immune enzymes activity, antioxidant status and ammonia resistance in Opsariichthys kaopingensis. Four hundred fifty healthy O. kaopingensis juveniles (6.21 ± 0.32 g) were randomly assigned to 15 tanks. Juvenile fish were fed five experimental diets containing microbial floc 0 (B0 control), 4% (B4), 8% (B8), 12% (B12) and 16% (B16), respectively, for 30 days. Results showed that B12 could significantly enhance weight gain rate (WGR), specific growth rate (SGR) and protein efficiency ratio (PER), reduce feed conversion rate (FCR) (p < .05), compared to the control. The activity of protease, lipase and amylase in hepatopancreas and gut of B12 group were higher than that of the control (p < .05). Also, significant increases in lysozyme (LSZ), glutamic pyruvic transaminase (GPT) and alkaline phosphatase (AKP) activities of O. kaopingensis were found at B12 group (p < .05). Comparing the antioxidant capacity, the activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), catalase (CAT) and ascorbic acid (ASA) of juveniles in B12 group were significant highly (p < .05) than control, and the content of malondialdehyde (MDA) was much lower than control in gill, kidney, hepatopancreas, intestine and serum under this experiment condition. After ammonia challenge, survival rate in all dietary supplementation of microbial floc treatment groups was significantly increased (p < .05). Overall, these findings suggest that dietary supplementation of microbial floc enhanced growth, digestion, antioxidant and immune response, and increased ammonia stress resistance in O. kaopingensis. The suitable supplemental level of approximately 12% microbial floc was recommended in the present study.