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

Abstract: Both nitrite (NO2–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 NO2–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 NO2–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 NO2–N. [Copyright &y& Elsevier]