Effects of fucoidan and quercetin on protecting crayfish (Procambarus clarkii) against infection with white spot syndrome virus.

White spot syndrome virus (WSSV) acts as a dangerous pathogen which threats the farming of crustaceans. This study aims to investigate the effect of diet supplemented with fucoidan and quercetin on the immunity and disease resistance of crayfish by studying the apoptosis of hemocytes, crayfish mortality rate and related immune parameters. The feed additive combination of 30 mg/kg fucoidan and 40 mg/kg quercetin (fucoidan + quercetin) significantly improved by 45 % the survival of crayfish (Procambarus clarkii) after infection with WSSV. The fucoidan + quercetin enhanced the total hemocyte counts in crayfish with or without WSSV infection. The combined diet of fucoidan and quercetin has a protective effect on the hemocytes of crayfish, and can reduce the apoptosis of hemocytes after WSSV infection. In addition, the combined diet of fucoidan and quercetin can affect the activities of various immune-related enzymes including superoxide dismutase (SOD), phenoloxidase (PO), catalase (CAT), lysozyme (LZM), acid phosphatase (ACP), and peroxidase (POD), thus modulating the related immune processes. In conclusion, the combination of fucoidan and quercetin can regulate crayfish's innate immunity and reduce mortality of crayfish after infection with WSSV.