Determination of heavy metal levels in Oreochromis niloticus and Chrysichthys nigrodigitatus from Ogun River, Nigeria

Comparison of heavy metal levels in Oreochromis niloticus and Chrysichthys nigrodigitatus caught in Ogun River (Nigeria) was carried out to reveal the potential health risks associated with fish consumption from the river. Concentrations of copper, lead and cadmium were determined in the gills, eyes, bone, flesh, liver and stomach of the fish species. Ten fish of each species were obtained commercially and analyzed for the metals using Atomic Absorption Spectrophotometer. Data obtained were subjected to one-way analysis of variance (ANOVA) at 5% significant level. The highest concentrations of Cu were observed in the gills of O. niloticus and the eyes followed by liver of C. nigrodigitatus, while the lowest concentrations were detected in the eyes of O. niloticus and bone of C. nigrodigitatus. Lead concentrations were higher in the liver of O. niloticus and gills of C. nigrodigitatus, while the lowest concentrations were detected in stomach of O. niloticus and C. nigrodigitatus respectively. Also, in proximate analysis, composition of dry matter, crude protein, crude fat, ash and carbohydrate contents recorded high in C. nigrodigitatus and O. niloticus and significantly differs. All the metals studied exceeded standard permissible limit for human consumption. Therefore, monitoring of the river is highly recommended, while adequate information, education and training should be strengthened to control further pollution.   Key words: Freshwater fish, Africa, contamination, Nile tilapia, catfish.