Tilapia piscidin 4 (TP4) enhances immune response, antioxidant activity, intestinal health and protection against Streptococcus iniae infection in Nile tilapia

Abstract Antimicrobial peptides (AMPs) are exploited as safe alternates to antibiotics application for controlling a wide range of bacteria, viruses, fungi, and parasitic infections in cultured fish. Therefore, tilapia piscidin 4 (TP4) dietary supplementation was evaluated in Nile tilapia (Oreochromis niloticus) on arrays of selected innate immune responses, oxidative stress, cytokine genes expression, microbial load, histopathological indices, and disease resistance against Streptococcus iniae (S. iniae). TP4 supplemented diets were formulated as; TP50 (group fed 50 mg/kg diet of TP4); and TP100 (group fed 100 mg/kg diet of TP4); besides a basal diet (control, no AMPs). Results showed that serum lysozyme, bactericidal, nitric oxide (NO), catalase (CAT) and superoxide dismutase (SOD) levels activities were all significantly increased at day 10 and 20. Interleukin- 8 (IL-8) and tumor necrosis factor- α (TNF-α) mRNA expression levels were upregulated at both TP50, 100 supplementations at day five then started to decline at day 10 and 20 compared to the control. Cumulative mortality rates were significantly decreased in both TP50, 100 groups compared to the control; whereas the lowest mortalities were observed in group TP100. The microbial load was significantly decreased in TP4 supplemented diets in both posterior kidney and intestine compared to control. Further, histopathological and scoring analysis proved a safe effect of TP4 on Nile tilapia. Our findings proposed that TP4 dietary supplementation could enhance immune response, antioxidant activity, and intestinal health furthermore it conferred protection against bacterial infections in Nile tilapia.