Effect of dietary poly-β-hydroxybutyrate on growth performance, feed utilization, water quality, immunity and ammonia stress tolerance in Penaeus vannamei post-larvae

The effects of dietary poly-β-hydroxybutyrate (PHB) supplementation on growth, feed utilization, water quality parameters and ammonia stress resistance of post-larval Pacific white shrimp ( Penaeus vannamei ) were investigated in this study. A fish meal-based basal diet (P0.0) was formulated and another four diets were prepared by incorporating 0.25%, 0.50%, 1.00% and 2.00% PHB into the basal diet (P.25, P.50, P1.0 and P2.0, respectively). Triplicate groups of treatment, each containing 100 similar-sized post-larvae (2.5 ± 0.3 mg) per tank (96 L), were fed with the relevant test diet three times a day for five weeks. At the end of the feeding trial, shrimp were challenged against a 48 h-LD 50 toxic ammonia concentration (0.150 ppm). Final body weight, weight gain, length gain, specific growth rate, feed conversion ratio and protein efficiency ratio of shrimp were not significantly affected. However, numerically higher final body weight and weight gain were shown by P.50 group, which was 31 mg higher in final body weight and 1,339% higher in weight gain compared to P0.0 treatment. P1.0 group showed a significantly higher survival than P0.0 and P2.0 groups. Prophenoloxidase ( proPO ) gene expression was significantly upregulated with dietary PHB supplementation at 0.25%–1.00% levels and the highest expression was observed in P1.0 group, which was 2.53 folds higher than P0.0 group. The water quality assessment test indicated that 2.00% PHB inclusion level significantly reduced water nitrite levels by 0.18 mg/L, but ammonia levels were not significantly affected. However, ammonia levels were reduced, showing a significant linear trend. At the end of the ammonia challenge, cumulative survivals in P0.0, P.25, P.50, P1.0 and P2.0 groups were 40.0%, 45.0%, 55.0%, 63.3% and 76.7%, respectively. proPO and lipopolysaccharide and β-1, 3-glucan-binding protein gene expressions in challenged shrimp were significantly upregulated in P1.0 and P2.0 groups compared to other groups. The results indicated that 1%–2% PHB in the diet can improve growth