Thiobencarb-induced changes in acetylcholinesterase activity of the fish Anguilla anguilla

European eels (Anguilla anguilla) were exposed to sublethal thiobencarb concentrations in a continuous flow-through system for 4 days. Brain, muscle, and gill acetylcholinesterase (AChE) activities were evaluated after 2, 12, 24, 48, 72, and 96 h herbicide exposure. Thiobencarb induced significant inhibitory effects, on the total and specific AChE activity of A. anguilla, ranging from >30-40% inhibition in eel brain and gills to >50% inhibition in muscle tissue 2 h after the initial exposure. In a second experiment, eels were exposed to thiobencarb for 96 h and then allowed a period of recovery in pesticide-free water. Following I week of recovery, the AChE activity of affected eels approached control level. Fish transferred to clean water recovered specific AChE activities in the studied tissues slowly in the next 8 days (without toxicant), reaching about 60-80% of the normal levels in brain and muscle tissue around the 4th day after the beginning of the recovery period (in clean water). Specific AChE activity in the gills from eels transferred to clean water recovered its normal value while total AChE activity remained depressed (29%) in this tissue 8 days later. Many behavioral changes such as lowering of motility with loss of equilibrium, uncoordinated movements, and increase in the levels of respiratory frequency were observed during exposure to the herbicide. (C) 2002 Elsevier Science (USA).