Behavioural Changes and Acetylcholinesterase Activity in Guppy Fish (Poecilia reticulata) Exposed to Chlorpyrifos

摘要

Chlorpyrifos is a broad spectrum organophosphate insecticide and potential toxic pollutant in aquatic ecosystems. Guppies were exposed to one-seventh (0.025 ppm/L) and one-fourteenth (0.0125 ppm/L) of the 96 h LC_(50) as sublethal concentrations for sub acute studies. The fish were exposed to both the sublethal concentrations for 96 h and allowed to recover in toxicant free medium for seven days only after sublethal exposure. Behavioural responses were studied in the experimental periods. Fish in toxic media exhibited irregular, erratic and darting swimming movements, hyper excitability, loss of equilibrium and sinking to the bottom. Fish were found under stress, but mortality was insignificant in both the sublethal concentrations. The behavioural changes may be due to the inhibition of acetylcholinesterase (AChE) activity. Inactivation of AChE activity results in excess accumulation of acetylcholine (ACh) in cholinergic synapses leading to hyper stimulation and cessation of neuronal transmission (paralysis). Impaired behavioural responses were observed even under recovery periods. This may be a consequence due to the inhibition of brain and muscular AChE activity by chlorpyrifos-oxon via biotransformation of bioaccumulated chlorpyrifos in the tissues.