Influence of Stocking Density on Growth Performance, Intestinal Antioxidant Status, and Immune‐Related Gene Expression of Endangered Megalobrama pellegrini Reared in a Flow‐Through System

Abstract

A 42-d feeding trial was conducted to evaluate the effects of stocking density on the growth and health status of juvenile Megalobrama pellegrini. Fish (initial body weight = 0.45 AE 0.01 g) were reared in a flow-through system under five stocking densities: 0.15, 0.24, 0.34, 0.42, and 0.50 kg/m 3 . Significantly lower growth performance (weight gain and specific growth rate) and a higher feed conversion ratio were recorded in fish reared at the highest stocking density (0.50 kg/m 3 ). Similarly, intestinal oxidative stress analyses indicated that activities of the antioxidant enzymes superoxide dismutase and catalase were reduced in M. pellegrini reared at the highest stocking density; the highest malondialdehyde content was also recorded in this group. In addition, intestinal glutathione content was significantly increased in higher-density groups compared with the lowest density group (0.15 kg/m 3 ), and the highest value appeared in the 0.34-kg/m 3 group. Intestinal CYP1A* (cytochrome P450 family 1 subfamily A gene) expression was significantly lower in the 0.15-kg/m 3 group than in the 0.42-kg/m 3 group. Furthermore, the 0.50-kg/m 3 group had significantly higher gene expression of Nrf2* (nuclear factor [erythroid-derived 2]-like 2), NF-κB* (nuclear factor kappa beta), and MyD88* (myeloid differentiation factor 88) than the lower-density groups. This study indicated that 0.45-1.36-g M. pellegrini could be cultured at a density of 0.34 kg/m 3 for maximum growth in a flow-through system without negative effects on the measured physiological indicators of stress and immunity.