Effect of sodium cyanide on the activities of some oxidative enzymes and metabolites in <i>Clarias gariepinus</i>

Abstract

The present study was conducted to determine the effect of sodium cyanide on oxidative metabolism, alterations in the activities of lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH), behavior, respiratory rate and metabolites (lactic and pyruvic acid) of the fingerling of Clarias gariepinus. The fingerlings were exposed to a sublethal concentration (0.75 mgL^-1) of sodium cyanide. Fish showed a gradual decrease in respiratory rate, increase in LDH and decrease in SDH levels, and lactic acid followed a similar trend with pyruvate in an eight-day trial. The changes in the levels of these enzyme activities may be as a result of impaired oxidative metabolism and cellular damage, which had effect on the release of these enzymes. Elevation in the level of lactic acid and decrease in pyruvic acid was due to shift from aerobic to anaerobic metabolism which resulted to a severe drop in the respiratory rate of the fish. It may be as a result of blockage of electron transfer from cytochrome-c oxidase to molecular oxygen which might lead to cellular hypoxia even in the presence of normal oxygenation of hemoglobin. Thus, inhibition of oxidative metabolism by sodium cyanide in C. garipenus was reconfirmed. Behavioral changes caused by sodium cyanide exposure in the fish were probably due to the combination of lactate acidosis with cytotoxic hypoxia, which might depress the central nervous system.

Key words: Succinate dehydrogenase (SDH), lactate dehydrogenase (LDH), lactic acid, pyruvate, behavior, enzymes.