Dietary magnolol inclusion improves the antioxidant and immune responses, and resistance to Aeromonas hydrophila in genetically improved farmed tilapia (Oreochromis niloticus)

A 10-week feeding trial was conducted to evaluate the effects of dietary magnolol inclusion on the growth rate, antioxidant and immune responses of genetically improved farmed tilapia Oreochromis niloticus. Four experimental diets were formulated with 0%, 0.02%, 0.04% and 0.08% magnolol, respectively. Dietary 0.02–0.08% magnolol inclusion did not affect the growth rate and feed utilization of tilapia. However, dietary 0.02–0.08% magnolol inclusion increased the plasma catalase, the intestinal alkaline phosphatase (ALP), and the hepatic glutathione reductase (GR) and catalase activities; but reduced the hepatic malondialdehyde (MDA) content. Further, supplementation with 0.04–0.08% magnolol increased the plasma superoxide dismutase (SOD), peroxidase, ALP and total antioxidant capacity (TAC), the intestinal GR, catalase, peroxidase and TAC, and the hepatic SOD and TAC activities; but decreased the plasma MDA, the intestinal MDA and reactive oxygen species contents. Dietary 0.02–0.04% magnolol inclusion increased the plasma complement 3 content, whereas the plasma immunoglobulin M, complement 4 contents and lysozyme activity were increased by dietary 0.04–0.08% magnolol inclusion. The phagocytic activity of head kidney macrophages was increased by the inclusion of 0.04% magnolol. Additionally, supplementation with 0.02–0.08% magnolol increased the relative percentage survival of tilapia after infection with Aeromonas hydrophila. These results indicated that 0.04% magnolol inclusion improved the antioxidant and immune responses without compromising growth performance of tilapia, suggesting that magnolol could be used as an antioxidant and immunostimulant in aquafeed.