Neurotoxic Effects of Imidacloprid on <i>Pethia conchonius</i> (Rosy Barb), a Common Freshwater Fish of India

Abstract

Insecticides are essential to control arthropod pests in agriculture. However, due to their stability and extended half-lives, they contaminate freshwater aquatic systems like lakes, ponds, and rivers by surface run-offs and leaching. Neonicotinoids are a globally used agricultural pesticides that act as an agonist to the nicotinic acetylcholine receptor (nAChRs) and are known to have harmful effects on non-target organisms like fish. This study aimed to determine the neurotoxic, behavioural, and histopathological effect of three sub-lethal concentrations (SLC I, SLC II, and SLC III) of Imidacloprid (IMI), a neonicotinoid, on the freshwater fish Pethia conchonius. Fish were exposed to IMI for 96 hr, during which their behaviour was recorded, and the brain tissues were collected at 24 hr intervals. Compared to the control group, the IMI-exposed fish showed changes in behaviour, such as jerky, erratic swimming, disequilibrium, and mucus secretion. A significant decrease in Acetylcholinesterase (AChE) activity and histopathological damage were recorded in the brain tissues. The severity of damage and decline in activity was both concentration and time-dependent. The AChE inhibition was observed for SLC III after 96 hr (33.70±2.52) compared to control at 96 hr (84.63±4.25). The optic tectum showed detachment in its layers along with necrosis, and vacuolation. The results indicate that IMI is highly neurotoxic which not only inhibits AChE activity but also causes neural damage in the brain leading to a wide range of behavioural alterations.