Short-term mercury exposure on Na(+)/K(+)-ATPase activity and ionoregulation in gill and brain of an Indian major carp, Cirrhinus mrigala.

Recently mercury pollution has been increased considerably in aquatic resources throughout the world and it is a growing global concern. In this study, the 96 h LC50 value of waterborne mercuric chloride for Cirrhinus mrigala was found to be 0.34 mg/L (with 95% confidence limits). Fingerlings of C. mrigala were exposed to 0.068 and 0.034 mg/L of mercuric chloride for 96 h to assess the Na(+)/K(+)-ATPase activity and ionoregulation (Na(+), K(+) and Cl(-)) in gill and brain. Results showed that Na(+)/K(+)-ATPase activity and ionic levels (Na(+), K(+) and Cl(-)) in gill and brain of fish exposed to different concentrations of mercuric chloride were found to be significantly (p<0.05) decreased throughout the study period. Mercury inactivates many enzymes by attaching to sulfur atoms in which the enzyme Na(+)/K(+)-ATPase is highly sensitive to mercury. The inhibition of gill and brain Na(+)/K(+)-ATPase activity might have resulted from the physicochemical alteration of the membrane due to mercury toxicity. Moreover, inhibition of Na(+)/K(+)-ATPase may affect the ion transport and osmoregulatory function by blocking the transport of substances across the membrane by active transport. The present study indicates that the alterations in these parameters can be used in environmental biomonitoring of mercury contamination in aquatic ecosystem.

Acute and sublethal effects in an Indian major carp Cirrhinus mrigala exposed to silver nitrate: Gill Na+/K+-ATPase, plasma electrolytes and biochemical alterations.

Due to prolonged use of silver in many applications, it enters into the freshwater and affects the aquatic organisms. Fingerlings of Cirrhinus mrigala were exposed to acute and sublethal concentrations of silver nitrate and the alterations of gill Na(+)/K(+)-ATPase, plasma electrolytes and biochemical parameters were assessed. The median lethal concentration of silver nitrate to the fish C. mrigala for 96 h was found to be 0.107 mg/l (with 95% confidence limits). 1/10th of LC 50 96 h value (0.0107 mg/l) was selected for sublethal study. During acute treatment branchial Na(+)/K(+)-ATPase activity was inhibited approximately 44.34% after 96 h of exposure. In sublethal treatment, silver nitrate could not produce a significant change in the activity of the enzyme at the end of 7th day. However, after 14th day, significant (p < 0.05) decrease was noted showing 22.52%-49.11% in rest of the study period. Silver intoxication resulted hyponatremia, hypokalemia, hypochloremia, and hypoproteinemia in both the treatments. Despite the decrease in these parameters, plasma glucose level was found to be increased in both the treatments to endure the silver toxicity. We suggest that the alterations in branchial Na(+)/K(+)-ATPase activity, plasma electrolytes, and biochemical parameters of fish may be useful in environmental biomonitoring and to assess the health of fish in freshwater habitat contaminated with silver.