Cypermethrin induced: In vivo inhibition of the acetylcholinesterase activity in functionally different tissues of the freshwater teleost, Labeo rohita (Hamilton)
ABSTRACT Effects of cypermethrin at different concentrations and exposure periods were investigated on the freshwater fish, Labeo rohita, to establish inhibitory effect of pesticide on acetyl cholinesterase (AChE) activity and associated behavioral changes. Fish were exposed to 1/7th (0.57 µg L-1) and 1/12th (0.33 µg L-1) of the lethal concentration (4 µg L-1) of cypermethrin for a period of 1, 7, or 14 days and allowed to recover for a further 7 days. Maximal inhibition in AChE activity in exposed fish was found in brain followed by muscle, gill, and liver on day 14 at both sublethal concentrations of cypermethrin. Recovery showed a rise in AChE activity but significantly decreased compared to controls. Depression of AChE activity suggests decreased cholinergic transmission and consequent accumulation of acetylcholine (ACh) in tissues leading to cessation of nerve impulses. This led to behavioral and morphological changes due to impaired neurophysiology in fish. Fish in toxic media exhibited erratic, and darting swimming movements, hyperexcitability, and loss of equilibrium and these symptoms persisted even during recovery.