الفهرس 
Title : Evaluation of oxidative stress, genotoxicity and gene expression alterations as biomarkers for metal pollution in Oreochromis niloticus and Clarias gariepinus in two different aquatic habitats
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Abstract
The impacts of the Batts drain on two chronically exposed fish (O. niloticus and C. gariepinus) were assessed using multiple biomarkers. Aqueous and sedimentary metal concentrations (Cu, Zn, Fe, Cd, Pb, and Al) showed significant elevations near the Batts discharges (site 2) compared to the reference site (site 1). The accumulation level of the analyzed metals in five vital tissues (liver, gills, kidney, muscle, and skin) was markedly elevated in site 2 compared to the reference samples. At the same site, C. gariepinus displayed the highest accumulation capacities compared to O. niloticus. Livers and kidneys, followed by gills, showed the maximum overall metal load based on the metal pollution index. Livers and gills 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. 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 expression levels of heat shock proteins (HSP-70) gene were upregulated in liver and gills tissues of both species (except for O.niloticus in liver tissues) in the polluted area (site 2) in comparison to the control area (site 1). The hazard index values for human consumption showed that the studied metals were within safe values at normal consumption rates. At the same time, harmful health consequences were observed at the habitual consumption level at site 2.