Microplastics in the water column and stomach contents of European perch (Perca fluviatilis) in a temperate lowland dam reservoir: a case study from the lower Vistula River

Abstract

Microplastics are of environmental concern because they are ubiquitous, persistent, and readily ingested by aquatic organisms. This study investigated the occurrence and characteristics of microplastics in the water column and in stomachs of juvenile European perch (Perca fluviatilis) in the Włocławek Reservoir, a large dam reservoir in Central Europe. Samples were collected in June 2024 from the nearshore zone in the central part of the reservoir. Water samples were filtered through 11 µm filters, and the retained material was digested with 30% hydrogen peroxide to remove organic matter. The samples were then re-filtered and examined under a stereomicroscope. Fish digestive tracts were dissected and analysed stereomicroscopically. For each identified microplastic particle, shape (fibres, ovals, flakes), colour, number, and size range were recorded. Ivlev's electivity index was used to assess selective ingestion of microplastics by fish. Microplastics were detected in reservoir water (188.7 particles per litre), in 25% (13 of 52) of the examined perch, and in the procedural blank (distilled water processed in the same way as reservoir water), where 24 particles per litre were found. Among fish containing microplastics, the mean number of particles per stomach was 2.08. Fibres dominated in the water column and were mostly blue, whereas only fibres were found in biological samples, where red fibres predominated. The results indicate a substantial microplastic contamination of the Włocławek Reservoir and demonstrate the presence of microplastics in the fish. However, the observed selectivity of microplastic uptake by fish from the water column remains unclear. The predominance of red fibres in stomach contents may indicate selective ingestion and/or differential retention of fibres in the digestive tract.