Abstract:Urea is an important factor for paddy production in paddy-crab ecosystem.However,application of urea may impose negative effects on the growth of crabs.In our research,the effects of different concentrations of urea on the non specific immune system of juvenile Eriocheir sinensis were studied in order to provide necessary theoretical support for setting up regulations for the paddy-crab ecosystem.The juvenile E.sinensis were reared in water containing 0.24,0.48,0.72,0.96,and 1.2 g/L urea respectively for 7 days without feeding.The activities of three enzymes including superoxide dismutase (SOD),catalase (CAT),and glutathione-S transferase (GST),as well as the content of malondialdehyde (MDA) in crab serum were determined.The results showed that the activities of SOD,CAT,and GST decreased gradually in crab serum for all urea concentrations during the experimental period,while the content of MDA increased instead.Also the activities of the above three enzymes showed a decreasing tendency as the urea concentration increased.However,the SOD activity in 024g/L and the GST activity in 0.96g/L urea treatments were significantly higher than those in the other urea treated groups,while the content of MDA in these two treatments decreased.The results suggest that the added urea reduces the E.sinensis's capability of eliminating lipid peroxides,hydrogen peroxide and free radicals.As a result,the non-specific defense system was damaged with the application of urea.
