Multiorgan Oxidative Damage and Gene Expression Modulation in Danio rerio Induced by Pollutants from the Tepetitlán Reservoir, Mexico

The Tepetitlán reservoir is affected by untreated domestic wastewater, agricultural runoff, and livestock-related discharges, posing risks to aquatic ecosystems. This study assessed its water quality and evaluated toxic effects on adult zebrafish (<i>Danio rerio</i>). Water samples from six sites (A-F) were analyzed for physicochemical parameters and the presence of metals and pharmaceuticals, quantified at concentrations in the µg L^-1 range. While most physicochemical parameters complied with Mexican regulations, true color exceeded established limits, and the presence of contaminants indicated environmental deterioration. Zebrafish were exposed to water from each site for 12, 24, 48, 72, and 96 h. Oxidative stress (OS) biomarkers were measured in the brain, gill, gut, and liver at all time points, and gene expression of antioxidant, detoxification, and apoptosis-related genes was assessed at 96 h in these organs. Significant OS was detected across sites, with increased lipid peroxidation, protein carbonylation, and hydroperoxide levels. Although antioxidant enzymes were activated, their response did not fully counteract oxidative damage. Gene expression analysis revealed upregulation of stress- and apoptosis-related genes. These findings demonstrate that the Tepetitlán reservoir contains pollutant mixtures capable of inducing oxidative and molecular stress responses in zebrafish, underlining potential ecological risks and the need for mitigation efforts.