Comparative Analysis of Microplastic Contamination in Wild and Enclosure-Reared Asian Seabass (Lates calcarifer) from the Southwestern Region of Bangladesh

Microplastic pollution threatens aquatic ecosystems and seafood safety worldwide, yet we still lack clear data on how different production environments affect fish exposure in South Asia. To address this, we compared microplastic contamination in wild river-caught and enclosure-reared Asian seabass (Lates calcarifer) from coastal Bangladesh, aiming to identify specific pollution sources, exposure pathways, and the resulting ecological risks. We excised the gastrointestinal tracts, gills, and dorsal muscle tissues from market-sourced fish. After digesting the organic matter with hydrogen peroxide, we isolated the plastic particles using zinc chloride density separation. We then characterized the particles’ morphology and surface weathering using optical and scanning electron microscopy and identified the polymer types with attenuated total reflectance Fourier-transform infrared spectroscopy. Our analysis showed that cultured fish had roughly twice the microplastic burden in their combined gastrointestinal and gill tissues (9.30 items per gram) compared to wild fish (4.35 items per gram). The contamination also reached the edible muscle, with 1.49 items per gram in cultured seabass and 2.19 in wild ones. Visually, 40.0% of the particles in enclosure fish were fibers and 38.9% were black, pointing to local farm infrastructure and degraded nets as the main sources. In contrast, wild fish contained mostly fragmented plastics (48.3%) from mixed urban runoff. Under the microscope, these particles showed extensive weathering, such as pits and cracks, and were often lodged deep in epidermal microcracks or coated in biofilm. These findings demonstrate that confined aquaculture setups act as hotspots for microplastic accumulation, increasing the likelihood of tissue translocation. To protect both fisheries and human consumers, we need to implement better waste management in regional watersheds and actively reduce plastic gear loss directly on the farms.