The histological effect on C. gariepinus exposed to aqueous extract of V. amygdalina was examined. One hundred and eighty (180) healthy juveniles of C. gariepinus (17.05±0.25g) were exposed to aqueous extracts of Vernonia amygdalina at concentrations at varying concentration of 0, 40, 45, 50, 55 and 60ml/l in replicates for 96h. Histological changes in the gills, liver and muscle were examined and used as an index of assessment. The gill histological changes observed were lesion and vacoulations, severe erosion of the secondary lamella, erosion of the gill mucus membrane. Abnormalities observed in the liver tissue of the treated fish were severe glycogenic vacoulation, cellular infiltration, hepatic necrosis, vacoular degeneration.Damage became severe at high concentrations and this could be detrimental to the health and wellbeing of the fish and can also have adverse effects on non-target species. Also, there was a significant reduction in DO of the test concentrations when compared with the control (0.0ml) . Highest value of DO (7.40±0.06) was observed in the control (0.0ml) and was significantly higher (P<0.05) than the test groups. The least value of DO (3.05±0.05) was observed in concentration 60ml of test plant. There were fluctuations in the values of the pH and temperature . The pH value decreased (7.50 ± 0.10) with an increasing concentration of V. amygdalina across the treatment. Highest pH value (7.50±0.02) was observed in the control (0.0ml) followed by treatment 2 (40ml) (7.44±0.04), while the lowest was observed in treatment 6 (60ml) with a value of (7.10±0.03) with no significant differences in temperature across the treatments. However, because of its medicinal and piscicidal property whose activities lie on the presence of their phytochemical compounds ( saponin, tannin, steroid, flavonoid, terpenoid, alkaloid and cardiac), and it could be used under control in management of fish ponds.

Keywords: Histological effect, Aqueous extract, clarias gariepinus, Vernonia amygdalina, , Histology