Sublethal effects of the herbicide thiobencarb on fecundity, histopathological and biochemical changes in the African catfish (Clarias gariepinus)

Fishes have been widely documented as useful bioindicator for ecotoxicological studies because of their differential sensitivity to pollution. Thus, the present study was carried out to determine the sub-lethal effects of commercial herbicide thiobencarb (CITRON®, 50EC) on the African catfish (Clarias gariepinus). Females fish were exposed to sub-lethal concentration of thiobencarb (½ LC50, 0.72 ppm) for 3, 9 and 15 days. Severe abnormality in the swimming behavior was observed in fish groups exposed for 9 and 15 days.  Adverse effects on the ovary and liver weights were observed. The absolute fecundity was significantly decreased by all thiobencarb-treatments, for which the lowest value  was observed at 15-day treatment in comparison with that of the control. A significant decline (p<0.01) in the activities of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) was observed in fish as the exposure period continued as compared to the control. Similarly, glucose and total protein levels were also significantly declined (p<0.01) with the exposure period. Histopathological changes in the liver tissue of fish exposed to thiobencarb were characterized by necrosis, changes in nuclear shape, formation of vacuoles and atrophy of hepatocytes. The ovary of fish exposed to thiobencarb for 15 days showed atretic vitellogenic oocytes and proliferation of follicular cells as well as inflammatory cells infiltration. These results indicate that thiobencarb is toxic and has the potential to impair on the physiological activities in African catfish. Therefore, the use of thiobencarb should be strongly controlled and carefully monitored to minimize its negative impacts on the aquatic ecosystems.