Insights into the interaction between stocking density and feeding rate in fish Megalobrama ambylcephala based on growth performance, innate immunity, antioxidant activity, and the GH-IGF1 axis

The interaction between stocking density and feeding rate was investigated in juvenile blunt snout bream (Megalobrama ambylcephala) (11.94 +/- 0.04 g) based on growth performance and health status. A 2 x 4 factorial design was adopted, containing two stocking densities (10 and 20 fish/m(3)) and four feeding rates (3%, 4%, 5% and 6% body weight/day). After the 12-weeks feeding trial, high stocking density (20 fish/m(3)) significantly (P < 0.05) reduced weight gain rate (WGR), feed intake (FI), protein efficiency ratio (PER), nitrogen and energy retention efficiency (NRE and ERE), plasma immunoglobulin M (IgM) level, plasma lysozyme (LZM), myeloperoxidase (MPO) and alkaline phosphatase (AKP) activities, as well as hepatic superoxide dismutase (SOD) and catalase (CAT) activities, while the opposite was observed in feed conversion rate (FCR), condition factor (CF) and plasma complement 4 (C4) level. The highest feeding rate (6%) significantly (P < 0.05) increased WGR, FI, FCR, CF, the intraperitoneal fat ratio and the protein expression of growth hormone receptor, but significantly (P < 0.001) decreased PER, NRE and ERE. Moderate feeding rates (4%-5%) significantly (P < 0.05) increased body lipid and energy contents, the activities of SOD, CAT, glutathione peroxidase, LZM, MPO, AKP and acid phosphatase, the levels of complement 3 and 4 (C3 and C4), and the transcriptions and protein levels of growth hormone and insulin-like growth factor 1, while the opposite was noted in the malondialdehyde content. Furthermore, an interactive effect between stocking density and feeding rate was also noted in WGR, FI, plasma ACP, AKP and MPO activities, and liver malondialdehyde content. In summary, stocking density and feeding rate interactively affect the growth performance and health status of blunt snout bream. The optimum feeding rate of this species increased when cultured under high-density conditions.