Histopathological changes in the liver and brain of fish exposed to endosulfan insecticide during tsetse fly control operations in Botswana

Abstract

During tsetse fly control operations, fish in the Okavango Delta region of Botswana are exposed to ultra–low–volume doses (6–12 g/ha) of endosulfan, an insecticide recognized to be highly toxic to fish. Approximately 1 % of the fish population can be killed by a spray, and the physiology and behaviour of survivors is temporarily disturbed. Simultaneously with the onset of the spraying season (July), the livers and brains of several species [including Clarias gariepinus (Burchell) and Tilapia rendalli (Boul.)] developed pathological lesions which often persisted until the season ended (October). Initially, hepatic lesions in C. gariepinus were characterized by generalized toxic necrosis, focal necrosis, and subcapsular oedema which gradually lessened in intensity and disappeared before the spraying season ended. Melano‐macrophage centres and perivascular haemopoietic elements were lost from poisoned livers and were not replaced until at least 6 months later. In T. rendalli brain, pesticide–related changes included encephalitis, meningitis and oedema, with an associated inflammatory infiltrate of eosinophilic granule cells. Most brain damage disappeared during the month after the spraying season, although glial scarring was occasionally observed in fish sampled later. The possible connection of these abnormalities with observed behavioural changes is discussed.