Improved growth and immunity in Nile tilapia Oreochromis niloticus fed a fermented rice bran supplement

Improvement of growth performance and disease resistance of cultured species is an important objective of the aquaculture industry. In this study, solid-state fermentation (SSF) was applied for increasing the nutritional value of rice bran with baker's yeast (Saccharomyces cerevisiae). Four diets containing different levels of fermented rice bran (FRB) at 0, 100, 200 and 300 g/kg (FRB0, FRB10, FRB20 and FRB30, respectively) were tested using juvenile Nile tilapia Oreochromis niloticus (average body weight = 5.22±0.02 g) for 56 days. Compared to FRB0, all diets improved growth performance of the experimental fish (P<0.05). Intestinal amylase and protease amounts were significantly increased (P<0.05). The experimental fish were intraperitoneally injected with Streptococcus agalactiae and the cumulative mortality rate was monitored for 10 days. All FRB-supplemented diets resulted in greater survival rates in challenge fish. The FRB20 and FRB30 diets promoted expression of insulin-like growth factor I (IGF-I) transcripts and enhanced non-specific immunity; lysozyme and antioxidant enzyme activities; myeloperoxidase (MPO), catalase (CAT), and superoxide dismutase (SOD) (P<0.05). The expression level of interleukin 8 (IL-8) was down-regulated in fish fed FRB20 and FRB30 (P<0.05) but IL-10 was up-regulated in fish fed FRB10 and FRB30 (P<0.05) while IL-1β was up-regulated in fish fed FRB20 (P<0.05). The expression of complementary 3 (C3) transcripts was significantly increased while nuclear factor-kappa B (NF-κB) was decreased in fish fed all FRB-supplemented diets (P<0.05). Conventional histology revealed increased villus height following FRB30 treatment (P<0.05). These results suggest the beneficial use of FRB supplementation on growth, immune defense and stress tolerance for juvenile O. niloticus.