Abstract:Poly-β-hydroxybutyrate (PHB) is a polymer of the short-chain fatty acid β-hydroxybutyrate. β-hydroxybutyric acid facilitates food digestion, absorption, and the protein and mineral utilization. The bacteria-derived PHB can be potentially used as an alternative to the conventional antibiotics in aqua-farming. Here we explored the effects of PHB on non-specific immunity of Litopenaeus vannamei. The L. vannamei was fed with baits containing PHB at different concentrations (0, 1.0%, 2.5% and 5.0%). The enzyme activities of the total antioxidant capacity (T-AOC), superoxide dismutase (SOD), peroxidase (POD) and lysozyme (LZM) in gill, hepatopancreas and serum were analyzed and compared among groups. The group with the best performance and the control group were selected for the ammonia stress test. After the NH4Cl treatment, we measured the concentration of malonaldehyde (MDA) and the expression levels of related genes in tissues by using real-time PCR. The results suggested that PHB affected the congenital immunity in the shrimp. As the concentration of PHB increased, the T-AOC activity in the experimental groups was first elevated followed by a decline. The activities of T-AOC in the serum, the hepatopancreas and the gill reached the maximum when the concentration of PHB was 2.5%, 2.5% and 1.0% respectively. The SOD activity in the gill and serum of shrimp fed with 5.0% PHB was significantly different from that in the control group. In the gill and hepatopancreas, the activity of POD and LZM peaked when the PHB concentration was 1.0% and 2.5% respectively. Compared with the control group, the POD activities of the experiment group supplemented with 1.0% and 2.5% PHB were 7.63-fold and 0.68-fold in the gill and hepatopancreas, and LZM activities were 1.88-fold and 1.18-fold, respectively. After the ammonia stress test, the shrimp fed with PHB showed lower MDA concentration than that without PHB, and the difference was significant in the serum (P<0.05). Furthermore, the expression levels of related genes were higher in the experimental groups compared to the control group. Our data indicated that PHB could improve non-specific immunity of shrimps.
