Evaluation of palmatine as an immunostimulant in diet for genetically improved farmed tilapia (GIFT, Oreochromis niloticus)

Palmatine as a medicinal herbs extract has strong bacteriostatic ability and is a promising source of antibacterial additive. The objective of this study was to assess the feasibility of palmatine as an antibiotic alternative in diet for genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Four experimental diets were formulated with 0, 200, 400, and 800 mg/kg palmatine. Tilapia with consistent size (initial body weight 3.43 ± 0.02 g) were fed the test diets twice daily for ten weeks. Dietary palmatine inclusion regardless of levels unaffected the growth performance and feed efficiency (P > 0.05). However, dietary 200–800 mg/kg palmatine inclusion reduced the levels of total cholesterol and low-density lipoprotein cholesterol as well as the ratios of low-density/high-density lipoprotein cholesterol and aspartate/alanine aminotransferase in serum (P < 0.05), but generally improved the antioxidant-related enzymes activities in intestine, plasma and liver, the immunoglobulin M, complement 3, and complement 4 contents and lysozyme activity in plasma, and the phagocytic activity of macrophages in head kidney. Bacterial challenge test demonstrated that dietary supplementation with 200–800 mg/kg palmatine enhanced the resistance of tilapia to Aeromonas hydrophila, and the relative percentage survival was the highest in fish fed diet with 400 mg/kg palmatine. In conclusion, dietary palmatine supplementation enhanced the antioxidant and innate immune responses as well as the resistance against A. hydrophila without compromising growth performance of tilapia, and the suitable inclusion level of palmatine was 400 mg/kg of diet for tilapia.