Acute toxic effects of chlorpyrifos on pseudobranchial neurosecretory system, brain regions and locomotory behavior of an air-breathing catfish, Heteropneustes fossilis (Bloch 1794)

In the late twentieth century, tremendous use of second-class organophosphate insecticides especially chlorpyrifos (CPF) resulting into heavy accumulation in different non-targeted aquatic species including fishes leads to apparent structural and biochemical changes in different organs and related abnormal behavioral responses. The present study has been undertaken as a pioneer attempt to assess the toxic effects of CPF on histopathological changes in pseudobranchial neurosecretory cells (PNSCs) of a neuroendocrine system of gill region, optic tectum (OT) and cerebellum, biochemical changes (acetylcholinesterase (AChE) activity and antioxidant markers) in the brain and associated locomotory behavioral alterations in air-breathing catfish, Heteropneustes fossilis. The fishes were exposed to CPF concentration of 1.92 mg/l for four days and their locomotor activities were recorded by ANY-MAZE software (Stoelting, Kiel, WI), an automated behavior tracking device. The acute exposure of CPF induced pathological changes in PNSCs, subtle changes in granular cells of the cerebellum and neuroarchitectural pattern of different layers of OT as compared to control. In the CPF exposed brain, AChE activity was significantly decreased while antioxidant enzymatic activity such as SOD activity was increased but CAT activity was substantially decreased. The CPF exposed fishes displayed significantly reduced locomotory activities with symptoms of motionless, loss of equilibrium and erratic movements. This study concludes that acute exposure to CPF for short duration may induce dys-regulation of neurosecretory activity of PNSCs, altered biochemical activity of brain and reduced locomotory/swimming performances in fishes.