Effects of garlic Allium sativum on the immune responses of olive flounder Paralichthys olivaceus

This study was aimed to investigate the effects of injection of garlic, Allium sativum, extract and immersion in garlic juice on the nonspecific immunity and the resistance against the artificial infection of Streptococcus iniae and Edwardsiella tarda of the olive flounder, Paralichthys olivaceus. The nonspecific immune mechanisms were assessed in terms of lysozyme activity, nitroblue-tetrazolium (NBT) assay and superoxide dismutase (SOD) activity etc. Relative percent survival (RPS) was assessed by the challenge with S. iniae BS10 or E. tarda KE-1. Almost of the garlic extract injected groups showed the enhanced level of the tested nonspecific immune factors. In the challenge test with S. iniae and E. tarda, RPS of 5% garlic extract pre-injected group was much higher than that of any other tested groups, respectively. Almost of the garlic juice immersion tested groups exhibited strengthened nonspecific immune defence factors, lysozyme activity, the number of lymphocytes and neutrophils, NBT reduction and SOD activity in kidney. In the challenge with S. iniae and E. tarda, RPS in the 0.25 g/L of garlic juice immersed group was much higher than any other tested groups, respectively. The results suggest that the garlic extract and juice would be effective to enhance the nonspecific immunity and protective ability of olive flounder against fish disease such as S. iniae and E. tarda.