Impacts of dietary phosphorus level on growth, antioxidant capacity and immunity in juvenile hybrid grouper (Epinephelus fuscoguttatus x E. lanceolatus ) fed with high-lipid diets

The study was designed to evaluate the effect of available phosphorus on growth performance, antioxidant capacity and non-specific immunity in hybrid grouper (female Epinephelus fuscoguttatus x male E. lanceolatus) fed with high-lipid diets. Juvenile fish (8.06 +/- 0.02 g) were subjected to six different dietary treatments over a period of eight weeks. These treatments consisted of diets (16% lipid level and 45% protein level) containing 0.3%, 0.58%, 0.67%, 0.76%, 0.85% and 0.94% available phosphorus (MCP), designated P1 (control), P2, P3, P4, P5 and P6, respectively. The results showed that (1) P1 group had suppressed final weight, weight gain and specific growth rate, while the other phosphorus experimental groups had significantly higher growth performance than the P1 group (P < 0.05). (2) With increasing phosphorus level, serum total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) enzyme activities increased significantly (P < 0.05). (3) With the increase in dietary phosphorus level, the reactive oxygen species (ROS) content in the liver was significantly decreased (P < 0.05). And the malondialdehyde (MDA) content was significantly decreased, while SOD, CAT, lysozyme (LYS), alkaline phosphatase (AKP), aspartate transaminase (AST) enzyme activities, T-AOC and IgM contents were significantly increased (P < 0.05) (4 The expression of antioxidant genes, such as hsp70, hsp90, sod, cat, gpx, were significantly higher in the appropriate phosphorus level groups than P1 group (P < 0.05), meanwhile the expression of proinflammatory factors, such as il6, il8, tnf alpha, was significantly reduced (P < 0.05). (6) In the attack experiment, the survival rate of P4 group was the highest, and the survival rate of P2 and P1 groups were the lowest. In conclusion, the appropriate addition of phosphorus can improve growth, antioxidant capacity of fish and disease resistance, and we recommend its addition at 0.67% to 0.77% in diet.