Histopathological Alterations in the Liver and Kidney of the Fish Chrysichthys nigrodigitatus due to Heavy Metals in Niger River

Surveillance and monitoring of concentrations of heavy metals in water bodies may serve as an early alert system on bioaccumulation of heavy metals in aquatic food chain therein. Histopathological examination of target tissues of the fish would reveal harmful effects of chemical pollutants like heavy metals in fish. This study determined the concentrations of heavy metals in water columns and in the fish Chrysichthys nigrodigitatus of Niger River at Onitsha as well as pathological alterations in liver and kidney tissues of the fish. Atomic Absorption Spectrophotometer was used in determination of concentrations (mg/l) of heavy metals namely, Zinc (Zn), Iron (Fe), Copper (Cu), Lead (Pb), Mercury (Hg), Cadmium (Cd), and Arsenic (As) in water and fish samples from the Niger River during the dry season of 2011 and proceeding wet season of 2012. Annual mean concentrations of Zn, Fe, Cu, Hg, Cd, and Arsenic in water columns were significantly lower (P<.05) than those in the fish. Annual mean concentrations of Zn, Cu, Cd, Hg, and Arsenic in fish however complied with WHO Standards in Aquatic Foods but Fe and Pb exceeded the WHO Standards. Extensive hyperaemia, oedematous sinusoids, hepatocytes in apoptosis with pyknotic nuclei, and wide spread necrotic hepatocytes with mononuclear leucocytes infiltrations and pigment deposits in liver tissues, as well as severe hyperaemia of the interstices with degenerating and necrotic tubular epithelial cells in kidney tissues were the major characteristic histopathological findings in the fish. Bioaccumulation of heavy metals in the fish indicated that Niger River at Onitsha was experiencing impairment, and that prolonged exposure of fish to heavy metals in the river may result in increased morbidity and mortality as well as reduced productivity in fish. Potential health risks associated with human consumption of heavy metal-contaminated fish and other aquatic food chain need not be over emphasized. Similar studies should be carried out in other Nigerian water bodies in order to increase the national information bank on chemical pollution which will help in the formulation of evidence-based policy decisions on methods of achieving sustainable environment. Keywords: Niger River, pollution, heavy metals, fish, bioaccumulation, liver and kidney, histopatholog