Effect of Echinacea purpurea extract on the immune system of rainbow trout (Oncorhynchus mykiss) and its resistance to Streptococcusis

In this study, some non-specific immune responses and hematological parameters in rainbow trout juveniles (16g mean weight) and their resistance to Streptococcusis were invetigated following dietary administration of 3 concentrations (0.5, 1, 1.5g/kg of feed) of Echinacea purpurea extract. The non-pecific immune response and hematological parameter compared with control group for 60 days. Evaluated parameters included were of C3, C4, (complement components), superoxide ions (respiratory burst), lysozyme activity, number of WBC, percentage of blood lymphocytes, monocytes and neutrophils. At the end of trial, the relative survival rate (RSR) of fish was evaluated against S. iniae. The results showed that the levels of C3, lysozyme activity, superoxide ions, number of WBC and percentage of neutrophils in the experiment groups (the highest concentration, 1.5g/kg of feed) were increased significantly compared to the control group. Whereas, no significant difference was found in the value of C4 and the percentage of monocytes and lymphocytes in comparison to the control group. The relative survival rates of fish following challenge with Streptococcus iniae, were 91.11 and 44.44 percent in experiment (Echinacea purpurea, concentration of 1.5g/kg of feed) and control group, respectively. In conclusion, the results of the present study demonstrated that Echinacea purpurea. extract enhanced the non-specific immune system and fish resistance against streptococcusis, suggesting that this extract might be used as immunostimulant in fish feed.