Responses of crucian carp Carassius auratus to long-term exposure to nitrite and low dissolved oxygen levels

Abstract

Both nitrite (NO 2 –N) and dissolved oxygen (DO) are key water quality factors and can impact on aquatic animals' health. In this study, juvenile crucian carp Carassius auratus were exposed to different concentrations of NO 2 –N (0, 2.5, and 5 mg L −1 ) and DO (2 and 6 mg L −1 ) for 30 days. Results showed that under low DO conditions there was a decrease in specific growth rate, feeding rate, food conversion efficiency, and protein efficiency ratio. Red blood cell count (RBC) increased significantly with decreasing DO; three-way ANOVA indicated that there was a statistically significant interaction between DO and NO 2 –N on RBC. Hemoglobin content of fish exposed to low DO levels was significantly higher than that in the normal DO. Changes in the enzymatic (SOD and CAT) and non-enzymatic (GSH) antioxidants in fish liver and blood exhibited oxidative stress occurred under the conditions of low DO and high NO 2 –N. ► Under low dissolved oxygen conditions there was a decrease in growth and feeding. ► Red blood cell count increased significantly with decreasing dissolved oxygen. ► There was a significant interaction between dissolved oxygen and nitrite on RBC. ► Hemoglobin content increased significantly with decreasing dissolved oxygen. ► Oxidative stress occurred under low dissolved oxygen and high nitrite.