VERIFICATION OF BENEFICIAL EFFECTS OF DIETARY PROBIOTICS IN ZEBRAFISH MODEL AND PRACTICAL APPLICATION IN TILAPIA AQUACULTURE

Zebrafish (Danio rerio) are an excellent model for assessing the beneficial effects of probiotics before applying them in aquaculture. This study evaluated the effects on zebrafish of dietary supplementation with the probiotic Bacillus amyloliquefaciens R8, which heterologously expresses xylanase from rumen fungi. Nutrient metabolism, hepatic oxidative stress, and innate immunity against pathogen infections were investigated. Treated zebrafish received feed supplemented with B. amyloliquefaciens R8 and then were compared to zebrafish that were fed a control diet. Results showed that the administration of B. amyloliquefaciens R8 can potentially improve nutrient metabolism and hepatic stress tolerance, and enhance immunity and disease resistance against A. hydrophila and S. agalactiae in zebrafish. The beneficial effects of probiotics were also validated in tilapia (Oreochromis niloticus) and demonstrated that dietary supplementation with xylanase-expressing B. amyloliquefaciens R8 improves growth performance and enhances immunity and disease resistance in Nile tilapia.

The livers of the probiotic-treated fish showed increased mRNA expressions of glycolysis-related genes and enzyme activities that are associated with fatty acid β-oxidation and mitochondrial integrity; decreased mRNA expressions of oxidative stress-related genes and an apoptotic tp53 gene (tp53). The probiotics-treated fish had increased expression of innate immune-related genes. Following challenge with A. hydrophila and S. agalactiae, probiotics-treated fish showed increased a higher survival rate than control fish. Growth and immune parameters were significantly increased in Nile tilapia fed probiotics for 2 months. In the present study, a probiotic with   multiple functions was shown to have practical applications in aquaculture.