Evaluation of sub-lethal effects of endosulfan on cortisol secretion, glutathione S-transferase and acetylcholinesterase activities in Clarias gariepinus

The effects of endosulfan, a widely used organochlorine pesticide in the Niger-Delta ecological zone were examined on cortisol secretion, glutathione S-transferase and acetylcholinesterase enzymatic activities in the serum of a dominant fresh water fish species, Clarias gariepinus. Juveniles stage of C. gariepinus were used for the toxicity study. Lethal concentration of 50% mortality of sample (LC50) was determined using semi-static method. From the result of the LC50 determination lower concentrations of endosulfan were prepared for sub-lethal test. Ten fish per test concentration in three replicates were exposed to varying concentrations of endosulfan (0.00, 0.0025, 0.005, 0.0075 and 0.01) mu g/L. Signs of stress and mortality were monitored during the experimental duration. Cortisol levels, GST and AChE activities were measured spectrophotometrically. No visible changes in behaviour and appearance were observed in the treated fishes and no mortality recorded. Significant (p < 0.05) declined in cortisol secretion was observed and the change in the concentration was dose and time dependent. Glutathione S-transferase activity was significantly (p < 0.05) higher than the control and the concentrations increase with increased in concentration and exposure duration. No clear trend was observed in acetylcholinesterase activity. The findings showed that the cortisol levels and GST activity of test organism were affected by the test chemical and therefore could be considered as a suitable marker to evaluate the effect of organochlorine pesticide on fish and other aquatic organisms. (C) 2010 Elsevier Ltd. All rights reserved.