Water contamination and cytogenetic effects in fish from coastal lagoons of southern Brazil

Coastal lagoons are ecologically sensitive environments increasingly exposed to human pressures, particularly in regions affected by seasonal tourism. These pressures may alter water quality and induce sublethal biological responses in aquatic organisms. This study evaluated physicochemical and microbiological parameters and cytogenetic biomarkers in the fish Geophagus iporangensis from nine lagoons within the Tramandaí River Basin (TRB), southern Brazil, sampled before, during, and after the summer vacation period. Water samples were analyzed for dissolved oxygen (DO) and thermotolerant coliforms (TC), while micronuclei (MN) and nuclear abnormalities (NA) were assessed in fish erythrocytes. DO concentrations in all samples complied with standards for the highest water quality class. In contrast, TC levels exceeded limits for primary contact recreation in eight lagoons in at least one sampling event, and four lagoons remained above these limits throughout all sampling periods. MN frequencies showed no significant spatial or temporal variation. NA frequencies ranged from 1.3 to 12.3‰ and exhibited significant spatial and temporal variability among lagoons. Seasonal population increases during the vacation period coincided with elevated fecal contamination in two lagoons and higher NA frequencies in four lagoons; however, no consistent seasonal pattern was observed across the study area. Moreover, no clear association was detected between TC concentrations and cytogenetic damage. These findings indicate that genotoxic responses in the TRB lagoons are influenced by lagoon specific and potentially diffuse contamination sources rather than by seasonal population increases alone. The co occurrence of fecal contamination and genotoxic responses raises concerns regarding environmental quality in coastal tourist areas.