Abstract:Nitrite is one of the most common stress factors in aquaculture water. In this study, the digestive enzyme activities in the hepatopancreas of Charybdis japonica under different concentrations of nitrite stress (0.15, 0.3, 2, 5, 10, 20mg/L) were measured by using bioenzymatic determination, and meanwhile the high concentration of nitrite stress (20mg/L) on the expression of tissue isozymes were also examined with polyacrylamid gel electrophoresis in order to explore the toxic mechanism of nitrite on aquatic crabs. The results showed that the activities of akaline protease, acid protease, lipase and amylase were all induced to some degree after exposure to lower concentrations of nitrite (0.15, 0.3mg/L). On day 7after exposure, all enzyme activities were still kept at high levels except the amylase activity was slightly lower than the control group. The activities of hepatopancreatic akaline protease, acid protease and lipase first increased rapidly, then following a dramatic decrease after exposure to moderate nitrite stress (2, 5, 10mg/L) for short time (0.5~1d). But higher concentration of nitrite stress (20mg/L), resulted in a significant inhibition of hepatopancreatic protease and amylase activities. On day 7after exposure, digestive enzyme activities showed a significantly negative correlation with increasing nitrite concentrations after the stress was over 2mg/L. The expression of α-amylase (α-AMY), lactate dehydrogenase (LDH), malic dehydrogenase (MDH) and peroxidase (POD) isozymes in gill, hepatopancreas, stomach, heart, ovum and sperm was significantly affected by high concentration of nitrite stress (20mg/L): isozyme activities declined or their expression bands reduced except that the muscle was induced to express MDH-2and MDH-4. The results indicated that high concentration of nitrite had a significant adverse effect on the digestive enzyme activities and the expression of tissue isozymes of C. japonica.