Background: Ingestion of microplastics (MPs) by commercially important fish, such as Bombay duck (Harpadon nehereus) can lead to the transport of MPs to humans and negatively impact health and physiology. Thus, assessment of the presence, type, and features of MP in this species is necessary to understand the possible impacts and adopt management measures. The purpose of this study was to determine the presence, occurrence and physicochemical features of MPs in the gastrointestinal tract of Bombay duck (H. nehereus) from the Patenga Sea Beach of the Bay of Bengal, Bangladesh. This area faces high amount of plastic discharge from the Karnaphuli River, industries, tourists, and urban households. Ninety-six fish were collected from the fishing trawlers of the Patenga Sea Beach. Their total length, body weight was measured and gastrointestinal tracts were separated for analysis. The samples underwent digestion, density separation, measurement, microscopic observation, and quantification. The color, type, and size were observed with microscopic image analysis software and polymer composition was determined with Fourier transform infrared spectroscopy method.
Results: The total items of MPs ranged from 25 to 198 per fish with a mean of 98.34 ± 53.11. There was a significant difference in the items of MPs among different sized fish (H = 74.656, p < 0.05). A significant positive correlation (ρ = 0.952, p < 0.05) was found between total length of fish and the number of MPs. Total 05 colors, 04 types and 03 size classes were observed. Filament type, blue color, and 500 μm to < 1 mm sized MPs were dominant. Four (04) types of polymers, polyethylene, polyurethane, polyamide, and polystyrene, were found.
Conclusions: The findings and insights from this study will help to understand the nature and extent of MP pollution in commercially important marine fish and possible impacts on the environment and humans.

Keywords: Bay of Bengal, Bombay duck, fisheries, microplastic, Patenga Sea Beach