From Anthropogenic Pressure to Biological Response: Microplastic Ingestion in the Wild Population of Alburnus alburnus Across Freshwater Reservoirs

Microplastics (MPs) are ubiquitous freshwater contaminants, but their associations with biological characteristics of wild fish remain insufficiently understood. This study investigated MP ingestion by the common bleak (Alburnus alburnus) across three Serbian reservoirs with contrasting anthropogenic influences, assessing spatial patterns of MP occurrence and abundance and their associations with fish characteristics. Microplastics were detected in 37.2% of individuals (n = 183), with significant differences among localities. Both occurrence and abundance were higher in reservoirs characterized by greater anthropogenic influence, while the comparatively lower-impact reservoir exhibited substantially lower values. Generalized linear models identified locality as a significant predictor of MP occurrence and abundance, revealing several-fold differences among reservoirs. Fulton’s condition factor (K) was significantly negatively associated with both MP occurrence and abundance, independently of locality, age class, and sex. Polymer analysis identified polyethylene (PE), polypropylene (PP), and ethylene-vinyl acetate (EVA), indicating variation in the composition of the ingested particles. These findings demonstrate spatial differences in MP ingestion and an association between MP contamination and fish body condition. Although causality cannot be established, the results support the potential of A. alburnus as a bioindicator of MP contamination in freshwater reservoirs.