Urbanization and the Level of Microplastic Ingestion by Fish: A Comparison of Freshwater Sunfish (Centrarchidae) from the Brazos River watershed, and Pinfish (Sparidae), from the Brazos Estuary and Inshore Marine Sites, Texas, USA

While previous research has documented ingestion of macro- and microplastics by aquatic fauna in both freshwater and marine ecosystems, relatively little is known of the environmental and ecological factors influencing the entry and diffusion of plastics and artificial polymers into aquatic foodwebs. Microplastics are defined as 50 μm to 5 mm in length. This study utilized stomach content analysis to compare the level of microplastic artificial polymer ingestion for fish collected from the Brazos River watershed, Brazos estuary, and inshore coastal waters of Texas, USA, in areas with varying levels of urbanization. We collected 318 bluegill (Lepomis macrochirus) and 118 longear sunfish (Lepomis megalotis) at 14 freshwater locales, and 11 samples of 298 pinfish (Lagodon rhomboides) at 6 saltwater locales. Sunfish averaged 12.6 cm in length, and pinfish averaged 14.9 cm. Sunfish averaged .807 microplastics per fish, and pinfish averaged 1.09. The maximum percentage for pinfish with microplastics present per sample (frequency) was 77%, compared to 75% for sunfish. Mean frequencies per sample were also similar: 45% for sunfish and 47% for pinfish. The Brazos River collections, however, had a greater percentage with frequencies of <.30 (42%) for sunfish, versus 9% for pinfish. Sample sites in the center of urbanized zones, including downtown Waco and Galveston, TX, had the greatest frequencies of ingestion, while sites upstream of Waco, TX, had the least. For pinfish, the mean stomach weight per sample was significantly positively correlated (p=.01) to both the percent of individuals ingesting microplastics (cc=.742) and the mean number of plastic particles ingested per fish (cc=.697). The majority of the microplastics were thread shaped, with blue and grey the dominant colors. Comparison with presence of natural food items suggests microplastic ingestion is predominantly incidental for these sentinel fish species.