Abamectin at environmentally-realistic concentrations cause oxidative stress and genotoxic damage in juvenile fish (Schizothorax prenanti)

Abamectin (ABM) has been extensively used in Chinese aquaculture systems for parasite control, but no information is available regarding its effects on the important freshwater commercial fish species Schizothorax prenanti. We performed an acute toxicity test to determine the effects of ABM on S. prenanti, and the 48- and 96-h median lethal concentration values were 33.32 and 15.98 mu g/L, respectively. In a second test, animals were exposed to sublethal concentrations of ABM (0.5, 2 or 8 mu g/L) for 8 days, and various cytological and biochemical parameters were measured. ABM caused DNA damage in hepatocytes, with significant increases in Olive Tail Moment values and 8-hydroxy-2'-deoxyguanosine levels. Hepatocytic apoptosis occurred following all treatments, and was accompanied by an increase in reactive oxygen species (ROS) generation and caspase activity in a dose- and time-dependent manner. In addition, there were significant decreases in glutathione peroxidase levels and superoxide dismutase and catalase activity and increases in malonaldehyde levels. ABM-induced hepatocytic apoptosis in S. prenanti was probably triggered by ROS generation following a cascade reaction of caspases in mitochondrial or death receptor pathways, which caused antioxidant inhibition, oxidative product accumulation, and DNA damage in the liver.