Impacts Of Circadian Rhythm And Melatonin On The Specific Activities Of Immune And Antioxidant Enzymes Of The Chinese Mitten Crab(Eriocheir Sinensis)

Many physiological functions of crustaceans show a rhythmic change to adapt to daily environmental cycles.However,daily variation in the immune and antioxidant status and its possible correlation with circulatory melatonin levels during the daily cycle have not been reported in the Chinese mitten crab,Eriocheir sinensis.In this study,the specific activities of immune and antioxidant enzymes of E.sinensis during a 24 h cycle and its relationship with injected doses of melatonin were evaluated.The results showed that the immune parameters in the hemolymph,such as total hemolymph count,alkaline phosphatase,lysozyme,acid phosphatase,and phenol oxidase,exhibited bimodal patterns during 24 h,which were synchronized with the activity of antioxidant enzymes such as malondialdehyde(MDA),superoxide dismutase(SOD),glutathione peroxidase,and catalase.However,there was only one peak in the muscles(during 1200 to 1600 hours)and in the gills(during 0400 to 0800 hours).The survival rate reached approximately 80% in 5 days when melatonin concentrations were lower than 0.05 g/L,significantly decreasing as melatonin concentrations increased.Four hours after injection,MDA levels in the muscle and hemolymph were significantly lower than those for the control group.Eight hours after injection,SOD levels in the hemolymph were significantly higher than those in the control group.The survival rate of E.sinensis was decreased with the increase of the dose of melatonin.In addition,compared with the control group,the activity of antioxidant enzymes such as malondialdehyde and superoxide dismutase in muscle and hematic of mitten crab was significantly reduced after injection of melatonin for4-8h.These findings highlight the importance of considering circadian regulation of innate immunity when comparing immune responses at fixed times.