Abstract

BEHAVIOURAL STUDY OF LEBISTES RETICULATUS EXPOSED TO ORGANOPHOSPHATE PESTICIDE

Sabiha Khan*

ABSTRACT

Lebistes reticulatus were exposed to different concentrations (0.245 to 0.300 mg/L) of an organophosphate pesticide, chlorpyrifos for 96 hrs and cadmium.0001mgm/l. The acute toxicity (LC50) of chlorpyrifos by static renewal (semi-static) bioassay test was found to be 0.284 mg/L. One-third (0.0946 mg/L) and one-sixth (0.0473 mg/L) of the 96 hrs LC50 were selected as sublethal concentrations for sub-acute studies. The fish were exposed to both the sublethal concentrations for 15, 30 and 45 days and were allowed to recover in toxicant free medium. Behavioural responses and morphological deformities 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. The fish were found under stress, but mortality was insignificant in both the sublethal concentrations. Caudal bending was the main morphological alteration during the exposure periods. The behavioural and morphological 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 hyperstimulation and cessation of neuronal transmission (paralysis). Impaired behavioural responses and morphological deformities 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.

Keywords: LC 50, Cadmium, Caudal bending, Chlorpyrifos, Lebistes reticulatus.