Effects of stocking density on the growth performance, serum biochemistry, muscle composition and HSP70 gene expression of juvenile golden pompano Trachinotus ovatus (Linnaeus, 1758)

Golden pompano (Trachinotus ovatus) is one of the most important cultured marine fish in Southeast Asia. Stocking density affects the growth performance and welfare of fish in aquaculture. A 70-day rearing experiment was performed to evaluate the effect of different stocking densities on the growth performance, feed conversion ratio, serum biochemistry, muscle quality, antioxidant capacity and HSP70 mRNA expression of juvenile golden pompano cultured in off-shore sea cages. The experimental design was completely randomized using three replications with three treatments: low (100 fish/m(3)), medium (200 fish/m(3)), and high (300 fish/m(3)) stocking densities. Fish growth decreased significantly, and the feed conversion ratio increased significantly with increasing stocking density (P < .05). The serum glucose concentration increased significantly (P < .05), and the total protein, total triglyceride and total cholesterol concentrations were significantly reduced with increasing stocking density (P < .05). High stocking density led to elevated serum cortisol levels and decreased thyroxine levels. There was a significant decrease in the muscular crude fat content with increasing stocking density (P < .05), while the moisture, ash and protein contents did not significantly differ among the groups (P > .05). In this experiment, superoxide dismutase, glutamine transaminase and total antioxidant capacity increased significantly with increasing stocking density (P < .05). The expression levels of heat shock protein 70 were significantly up-regulated in the liver, kidney and brain as stocking density increased (P < .05); however, there was no significant difference in the spleen (P > .05). Overall, high stocking density was a chronic stressor in this experiment and had a negative effect on the growth, feed conversion ratio and animal welfare of T. ovatus.