Microplastics reach organs outside the gastrointestinal tract of yellow perch (Perca flavescens) following long-term exposure in large, in-lake mesocosms

Microplastics (1–5,000 µm) in aquatic ecosystems are ingested by fish, impacting feeding, digestion, growth, and immunity. Their translocation to tissues (liver, muscle) remains poorly understood, especially for larger particles observed in wild fish. We exposed yearling yellow perch (Perca flavescens) for 10 weeks to environmentally relevant and projected future scenario concentrations of polyethylene, polystyrene, and polyethylene terephthalate microplastics (5–1,960 µm) in in-lake mesocosms. Seven of nine mesocosms received 6–29,240 particles L⁻¹. We quantified microplastic (>53-µm) ingestion in gastrointestinal tracts (GITs), and translocation in liver and muscle. Ingestion increased with nominal microplastic loading concentration (0–721 particles per fish, n = 28), but translocation to liver and muscle was rare (0–5 particles per fish) and not related to loading concentration. Liver particles were 50% shorter and 51% narrower than in GIT, and muscle particles were 5% narrower, on average. Relative to all particles added to the mesocosms, GIT and muscle particles were 81 and 82% longer, while liver particles were 9% shorter, on average. Overall, yellow perch ingested microplastics in proportion to environmental concentrations, with limited translocation of smaller particles to organs (counts were 4% in liver and 7% in muscle of those in GITs, on average) although the mechanism remains unclear.