The impacts of the Batts drain on two chronically exposed fish (O. niloticus and C. gariepinus) were assessed using multiple biomarkers. Concentrations of metals in water and sediments (Cu, Zn, Fe, Cd, Pb, and Al) showed significant elevations near the Batts discharges (site 2) compared to the reference site (site 1). The liver and gills of fish collected from site 2 showed marked elevations in the catalase, superoxide dismutase, glutathione peroxidase, and thiobarbituric acid reactive substance levels. In addition, significant reductions in glutathione-reduced contents were also recorded. Tissue and species-specific antioxidant responses were associated with excessive generations of reactive oxygen species, which were visualized fluorescently. Various histological alterations were observed in the gills and livers of both species. These alterations varied between compensatory responses (ex: epithelial thickening and lifting) and irreversible damage (ex: necrotic degeneration). Based on the level of lipid peroxidation and the frequency of histopathological modifications, O. niloticus demonstrated greater resistance to the same level of pollution than C. gariepinus. Using integrated biomarkers to evaluate the real impacts of untreated discharges of the Batts drain is applied for the first time on the selected fish species at the studied sites.

The present work showed the impact of long-term exposure to the Batts drain’s discharges on O. niloticus and C. gariepinus fish species. The accumulation level of Cu, Zn, Fe, Cd, Pb and Al in five vital tissues was markedly elevated near the Batts drain (site2) compared to the samples from the reference site (site 1). At the same site, C. gariepinus displayed the highest accumulation capacities when compared to O. niloticus. Based on the metal pollution index, livers and kidneys, followed by gills, showed the maximum overall metal load. The degree of DNA damage (assessed by comet and diphenylamine assays) was relative to the accumulated metals in tissues with species and site specification. The values of the hazard index for human consumption showed that the studied metals were within safe values at normal consumption rates. While harmful health consequences were observed at the habitual consumption level at site 2.