Comparative histopathological studies of selected organs of Oreochromis niloticus (Linnaeus, 1758) from Igun and Opa Reservoirs, Southwestern Nigeria

Heavy metals have been reported to have negative impacts on the histology of fishes. In this study, the impact of heavy metal bioaccumulation on the gills, muscle and liver of Oreochromis niloticus from Opa and Igun reservoirs was determined by histological methods. This was with a view to checking for possible alterations on fish organs. Live fish samples were collected from Opa and Igun reservoirs and identified in the laboratory. Histological analyses were carried out on the organs and their photomicrographs taken using digital binocular compound LED microscope. The gills of O. niloticus from Opa and Igun reservoirs showed hyperplasia of secondary lamellae and hypertrophy of primary lamellae while shortening and edema of secondary lamellae were observed in O. niloticus from Opa reservoir only. Muscular atrophy and degeneration were revealed in the muscle of fish from the two reservoirs with muscular splitting in O. niloticus from Igun reservoir. The liver of O. niloticus from Opa reservoir showed vascular congestion in the bile duct compared to O. niloticus from Igun reservoir which showed hepatopancreas degeneration, melanomacrophages aggregates, nucleus and hepatocytes hypertrophy. In conclusion, histopathological alterations were more severe in the organs of O. niloticus from Igun reservoir compared to that from Opa reservoir.