Effects of dietary antimicrobial peptides on growth performance, antioxidant capacity, immune response and disease resistance of juvenile Nile tilapia (Oreochromis niloticus)

Abstract

Introduction The study was conducted to investigate effects of dietary antimicrobial peptide, tilapia-derived endogenous piscidin 4 (TP4), on growth performance, antioxidant capacity, immune response and disease resistance of juvenile Nile Tilapia (Oreochromis niloticus). Methods Four diets with supplementation of 0 g/kg (Control), 2.0 g/kg, 4.0 g/kg, and 8.0 g/kg of TP4, respectively, were prepared for tilapia (initial weight 11.67 ± 0.21 g). Results Results showed that specific growth rate of fish fed the diet with 2.0 g/kg TP4 was significantly higher, while feed conversion ratio was lower than those in the control (P < 0.05). Meanwhile, 2.0 g/kg TP4 supplementation markedly elevated crude protein contents and condition factor, as well as intestinal trypsin and lipase activities than the control (P < 0.05). In addition, 2.0 and 4.0 g/kg TP4 supplementation enhanced antioxidant capacity, evidenced by significantly increased catalase and peroxidase activities, as well as decreased malondialdehyde contents in liver (P < 0.05). Moreover, the expression of antioxidant genes sod1, cat, nrf2 and atf4 was higher significantly in 2.0 and 4.0 g/kg TP4 groups than in the control (P < 0.05). Also, 2.0 g/kg TP4 supplementation significantly reduced activities of glutamic-oxalacetic transaminase and glutamic-pyruvic transaminase and elevated the activity of alkaline phosphatase (P < 0.05). Relatedly, pro-inflammatory genes il8 and tnfα were downregulated, anti-inflammatory genes il10 and arg1 were upregulated, and relative percent survival of fish after challenge with Streptococcus agalactiae was elevated in the 2.0 g/kg TP4 group than in the control, demonstrating that 2.0 g/kg TP4 may improve immune response and disease resistance. However, these favorable effects on antioxidant capacity and immunity disappeared at the 8.0 g/kg TP4 supplementation level. Discussion In conclusion, 2-4 g/kg TP4 supplementation in the diet effectively enhanced antioxidant capacity, immune response and disease resistance, which may potentially improve the growth performance.