One of the many biomarkers for determining the effects of pollutants on fish is changes in organ histopathology. Leaves of Balanites aegyptiaca have been reported to have phytochemicals with fish anaesthetic property. This study sought to determine the effect of graded acute concentrations (200.00, 250.00, 300.00.350.00 and 400.00 mg/L) of
B. aegyptiaca on histopathology of gills, kidney and liver of mixed sex of Oreochromis niloticus fingerlings. A total of 120 O. niloticus fingerlings (mean weight 23±0.03 g and mean total length 12.50±0.39 cm) were exposed to the plant extract. Paraffin wax method and haematoxylin-eosin staining techniques of tissue processing were adopted for
the examination of the gills, kidney and liver. Dose-dependent histopathological changes were observed in the three organs (gills, kidney and liver) i.e. histopathological alterations increase with increase in concentration of the plant extract. Gills showed lamellae fusion, haemorrhage, desquamation, atrophy and secondary lamellae erosion while
kidney and liver indicated atrophy, necrosis, haemorrhage, hyperplasia and hypertrophy. Structural alterations were evident in the gills, kidney and liver of O. niloticus fingerlings exposed to the concentrations of aqueous crude leaf extract of B. aegyptiaca therefore it should be used with caution during fish anaesthesia.