Andalin (25% EC), the trade name of flucycloxuron (FCX), is a chitin synthesis inhibitor belonging to the class of benzoylphenylurea. It was found a potent insecticide against mosquito larvae. In this present study we evaluate the toxicity of this insecticide on acetylcholinesterase (AChE) and catalase activities (CAT) in adult females of a larvivorous fish, Gambusia affinis (Teleosteen: Poeciliidae). This fish is extensively used in biological control of mosquitoes. The insecticide was added in rearing water at two concentrations corresponding to LC50 and LC90 previously obtained against fourth instars larvae of Culex pipiens (Diptera: Culicidae). The female adults were exposed to a continuous treatment for 28 days, and AChE and CAT activities determined at different exposure times (0, 7, 14, 21 and 28 days). FCX was found to cause inhibition in AChE activity and induction in CAT activity starting day 14. In a second experiment, exposed fish were transferred to clean water up to 8 days to asses the recovery pattern. Exposed fish gradually restored to the control values by day 4 and 8 in the LC50- and LC90-treated series, while CAT activity was recovered after 2 days for the LC50 and 4 days for the LC90. The overall data obtained suggested that G. affinis is a suitable biological model which can be used in toxicological and biomonitoring studies, and CAT activity is a good biomarker of oxidative stress induced by such insecticides. Moreover, it stimulated rapidly the antioxidant enzyme activities. The recovery pattern showed that this fish species was able to overcome relatively rapidly the toxic stress induced by this insecticide. Finally, this insecticide appears less toxic against G. affinis than the conventional insecticides.
