Microplastic ingestion in invasive mosquitofish (Gambusia holbrooki): a nationwide survey from Türkiye

Abstract Microplastics are widespread pollutants in freshwater ecosystems, yet comprehensive data on their occurrence across large geographic scales remains scarce. This nationwide study, therefore, examined microplastic ingestion in 621 individuals of non-native Gambusia holbrooki across 24 freshwater sites in Türkiye, selected to represent diverse hydrological types and anthropogenic pressures. Microplastic particles were extracted from the gastrointestinal tracts and analyzed for morphology, polymer type, size, and color using stereomicroscopy and ATR-FTIR spectroscopy. Fibers were the dominant shape (66%), followed by fragments (23%), films (9%), and spheres (2%). The most common polymer types were polyethylene terephthalate (PET, 40%) and polyethylene (PE, 28%), while black (35%) and blue (22%) were the most frequent colors. Over 80% of particles measured less than 1 mm in size. Microplastic loads were higher in lentic systems and areas influenced by agricultural or domestic discharge, highlighting spatial variability driven by land use and waterbody type. This pattern aligns with the ecology of G. holbrooki, whose surface-feeding behavior and preference for lentic waters likely increase its exposure to microplastics. These findings demonstrate the utility of G. holbrooki as a bioindicator of localized microplastic pollution. Future monitoring programs should integrate land-use data and adopt multi-species approaches to capture the full spectrum of contamination. This study supports the inclusion of adaptable, invasive species in cost-effective freshwater pollution assessments and informs targeted management strategies. Graphical Abstract