Tracing microplastics in fish: Uptake, translocation, and multidimensional biological impacts

Since the 1960s, global plastic production has increased dramatically, resulting in widespread accumulation and fragmentation of plastic debris in terrestrial, aquatic, and atmospheric systems. Microplastics (MPs), originating from primary sources such as industrial raw materials and microbeads, as well as secondary sources from fragmentation of larger plastics, have emerged as contaminants of particular concern due to their persistence, high abundance, and capacity to interact with diverse organisms. This review provides a comprehensive overview of microplastic behavior, focusing on fish as key bioindicators. We summarize the environmental distribution of microplastics, their uptake pathways, bioaccumulation and potential trophic transfer, organ-level and cellular translocation, and clearance mechanisms in fish, integrating both laboratory and field observations. Advanced analytical and imaging techniques-including fluorescence labeling, molecular and metal probes, isotopic tracing, hyperspectral imaging, and surface-enhanced Raman spectroscopy-are evaluated for their advantages, limitations, and reliability in detecting MPs. Furthermore, we synthesize evidence on the multifaceted effects of MPs on fish growth, development, behavior, antioxidant capacity, immune function, and gut microbiota. This review uniquely highlights the full pathway of MPs from environmental exposure to organismal impact, providing critical insights into their ecological risks, methodological considerations, and implications for environmental monitoring and pollution mitigation.