Effects of Caspian trout antimicrobial peptide Hepcidin in controlling in vivo Streptococcus iniae infection and its effect on the expression of cytokine genes in Caspian trout (Salmo trutta caspius)

Hepcidins are a group of cysteine-rich antimicrobial peptides that are active in fish against gram-positive and gram-negative bacteria as well as viruses. The objective of the present study is to use the synthetic peptide of Caspian trout Hepcidin (CtHep) for controlling in vivo Streptococcus iniae infection and also to study the immunomodulatory effects of CtHep in Caspian trout. Juvenile Caspian trout with average weight of 20 g were injected with synthetic CtHep at a dose of 1 µg/g fish, and then exposed to S. iniae bacteria. After 24 hours, the expression of cytokine genes and total bacterial load were evaluated in kidney and spleen tissues of different groups. Fish survival rate was noticed until 10th day of infection. The expression of IL-1β, IL-6 and TNF-α mRNA in CtHep-receiving group significantly increased compared to the control group. In addition, total bacterial load in the kidney and spleen tissues of infected fish receiving CtHep, was significantly lower than infected fish which did not receive CtHep. Survival rate of infected fish receiving CtHep was considerably higher than that of the infected fish which did not receive CtHep. Our study shows that CtHep has the potential to be used as an antimicrobial agent as well as an immunostimulant in aquaculture industry.