Invasive mosquitofish (Gambusia holbrooki) have longer gill telomeres in polluted and mesohaline habitats

Chemical pollution is a widespread stressor for wild organisms, but its effects on molecular damage and aging are still poorly understood. Telomere attrition has been used as an integrative biomarker of aging and stress exposure in endotherms. However, the effects of organic pollution on telomere length remain unclear, especially in ectotherms such as fish. We compared telomere length in fish gills across different populations of a short-lived invasive species, the mosquitofish ( Gambusia holbrooki ), exposed to organic pollution, or salinity. We expected lower telomere length in fish from more polluted and/or saline habitats due to increased oxidative stress. Contrary to our predictions, telomere length was unchanged in agricultural and port habitats and was higher in populations exposed to increased salinity and industrial pollution. A significant change in oxidative stress status in the liver was observed in response to increased salinity but no clear response was evident regarding pollution. Although the underlying mechanisms remain to be explored, this study suggests protective processes limiting telomere attrition or selective processes favoring individuals with longer telomeres. We also encourage further empirical approaches to study telomere attrition in aquatic ectotherms, particularly in fish exposed to multiple environmental stressors. • Gill telomere length was measured in mosquitofish across stressful environments. • Mosquitofish had longer telomeres in mesohaline and industrial habitats. • Mosquitofish had a poorer liver oxidative status in mesohaline habitats. • There was no evident link between antioxidant status and telomere length.