Occurrence of heavy metals in selected fish species of River Oli, Kainji Lake National Park, Nigeria
Heavy metals have long been documented as serious pollutants of the aquatic system because its contamination may have devastating effects on the ecological stability of the receiving environment. Therefore, this study assessed the concentration of heavy metals in three selected fish species from River Oli in Kainji Lake National Park to ensure continuous safety for sustainable production within the protected area. Nine sub-adult specimens, three each of Lates niloticus (Nile perch), Hydrocynus forskalii, (Tiger fish) and Synodontis membranacea (Upside-down catfish) were caught monthly using set gill nets for three months. All samples were labeled, processed and analyzed using Atomic Absorption Spectrophotometer. The result revealed that gills, bones, and muscles of the sample species contain significantly varying (p<0.05) concentration of Fe, Pb, Cu, Zn, Cr, and Cd. The highest mean concentration of Pb (4.80±0.12), Zn (24.46±4.33) and Cu (29.55±1.15) were found in H. forskalii flesh muscles also. There is significant (p<0.05) high level of Pb (2.65±0.04) bioaccumulation in the gill of H. forskalii while Cr (17.00±0.21) is higher in S. membranacea gills. The highest concentrations of Pb (4.05±0.03), Cr (11.55±0.56) and Cu (31.85±1.04) were again recorded in S. membranacea bones, while Fe (232.04±9.88) and Zn (39.35±1.24) highly accumulated in the vertebral bone of L. niloticus and H. forskalii, respectively. The concentrations of Pb and Fe in the whole fish of all sampled species are above maximum permissible limit according to the WHO standard for foods. Heavy metal elements in L. niloticus and H. forskalii have similar association pattern of Fe>Zn>Cu> Cr>Pb>Cd which slightly differ from Fe>Cu>Zn>Cr>Pb>Cd obtained for S. membranacea. This study revealed that fish can bio accumulate these heavy metals in different body parts from polluted water, whichmay lead to ecological adversity as result of impairment or loss of natural population.