Sarotherodon mossambicus were fed a chicken manure (60%) supplementary diet for 4 weeks under laboratory conditions, and significantly higher (P less than 0.05) concentrations of Mn, Fe, Cu, Pb, and Zn were obtained in the gills of the treated fish. Ultrastructural changes including separation of the epithelium from the pillar cell system and subsequently increasing the blood-water barrier, necrosis of lamellar cells, collapse of lamellar blood spaces, and hyperplasia of interlamellar cells were found in the lamellae of the gills of the treated fish.