Enzymatic responses of fish (Ctenopharyngodon idella) exposed to lethal concentrations of selected trace metals.

Six sampled tissues were selected to measure their respective enzyme activities through spectrophotometric method. Drastic changes were observed in the enzyme activities of fish under the influence of LC15, LC50 and LC85 copper, chromium and lead administered metals respectively. Significant decrease (p < 0.05) in acetylcholine esterase activity was noted in the metals stressed brain tissue for each of the exposure concentrations as compared to the reference group, whereas among the anti-oxidant enzymes, catalase (CAT) level in stressed liver tissue had a significant increase (p < 0.05) against the respective exposure concentrations. Unlike CAT enzyme level, superoxide dismutase (SOD) in muscle tissue, dropped significantly to nearly negligible level as compared to control group where SOD activity was of maximum level. Since, the levels of enzyme activity effected by the three metals in the entire experimentation were found in a decreasing order of chromium > copper > lead, consequently a prominent level (p < 0.05) of SOD was confirmed at the heaviest exposure concentration (LC85) by chromium during 96 h of time interval. To combat the free radicals produced as result of metals exposure, gluthathione peroxidase activity dramatically increased by nearly 95% as compared to the reference group. Sodium-potassium adenosine triphosphatase (Na + -K + -ATPase) activity in gills significantly decreased in the first metal treated group and returned to the normal levels in the second (LC50) and third treated group (LC85) in case of chromium and copper respectively. Nevertheless, the values obtained for the digestive enzyme pepsin in the fish intestinal tissue had imprecise results.