ABSTRACT
The sublethal concentration 6 mg.l-1 of a piscicidal flavanoid, 'Quercetin glycoside', obtained from E. colebrookiana affected neuro-architecture in medulla oblongata of freshwater fish, Barilius bendelisis (Ham.), at 32 days exposure. Since medulla of fish is primary centre for the reception of several incoming stimuli, the breakdown of neurons and their neuraxes in facial and vagal lobes impaired the transmission of sensory informations to cerebellum. Consequently fish became unconscious and could be caught easily with hands. The symptoms like lack of schooling, lack of response to food and external stimuli, sluggishness, incapability of maintaining body posture and uncoordinated functioning are accounted for by the neurolysis in hind brain of fish.