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Feeding habits and microplastic ingestion of short mackerel, Rastrelliger brachysoma, in a tropical estuarine environment
Summary
Analysis of 541 short mackerel from Thailand's Pattani Bay found microplastics constituting only 0.35% of stomach contents despite comprising 7% of ambient plankton samples, with ingestion occurring incidentally regardless of fish size, depth, or season. This selective feeding pattern suggests microplastic ingestion may be more widespread in planktivorous fish than stomach content analysis implies, with implications for seafood safety and marine food chain contamination.
This study aimed to assess diet characteristics and ingestion of microplastics (MPs) by short mackerel (Rastrelliger brachysoma) based on fish size, water, depth, and season. Samples of fish were collected monthly from three depth contours during February 2019 and February 2020 by mackerel gill nets in the mouth area of Pattani Bay, Thailand. Plankton samples in the natural environment were simultaneously collected with fish sampling. Altogether, 541 individuals were used for stomach content analysis. The fish fullness index (FI) was influenced by season (p < 0.001), while the average number of food types (AF) was affected by fish size (p < 0.001) and season (p = 0.003). This fish is a specific planktonic feeder with a slightly low trophic level (2.39) and diet breadth (0.27). Diatoms (46.80%), calanoid copepods (15.85%), and dinoflagellates (13.95%) were the main food types found in the stomachs. While in the natural habitat, MPs contributed 7.04% of plankton samples, in this study, R. brachysoma stomach analysis found MPs contributed 0.35%. The ingestion of MPs was not affected by fish size, water depth or season (p > 0.05). The colors of MPs found were mostly blue, followed by green, red, and fragment. Based on diet composition and the prey selectivity index (-0.9), it is thus concluded that MPs are accidentally ingested by this species.