EFFECTS OF THE ORGANOPHOSPHATE INSECTICIDE, MONOCROTOPHOS, ON ACETYLCHOLINESTERASE ACTIVITY IN THE NILE TILAPIA FISH (OREOCHROMIS-NILOTICUS) BRAIN

The neurotoxic effects of monocrotophos on the brain of the nile tilap ia fish (Oreochromis niloticus) were examined, using a static bioassay under laboratory conditions. By probit analysis the 96 h LC(50) value of monocrotophos was 4.9 mg/l. After 96 h exposure to acute levels of monocrotophos, the brain acetylcholinesterase (AChE) activity decreas ed progressively as the concentration of monocrotophos increased. In a ddition, four weeks following transfer to toxicant-free water after ex posure to 1 mg monocrotophos, nile tilapia fish brain regained 95% of control AChE activity. The results indicate that inhibition of AChE ac tivity in fish exposed to monocrotophos may serve as an indicator of h azard due to application of this chemical in the natural environment.