Semester of Graduation



Master of Science (MS)


Oceanography and Environmental Sciences

Document Type



Microplastics are plastic particles less than 5mm that come from different sources, such as industrial products, cosmetics, and the breakdown of the macroplastics. Microplastics derive from terrestrial sources but concentrate in flowing freshwaters where they may enter aquatic food webs. The northern Gulf of Mexico has shown very high microplastic concentrations, which are assumed to be sourced from the Mississippi River and its watershed. This study seeks to study microplastics in fish in the Mississippi River and the Gulf of Mexico. Fish stomachs and intestines from fish underwent chemical digestion, filtration, and microplastics identification and enumeration through FT-IR spectrometry. Chapter one seeks to quantify microplastics in four different fish species (Shortnose Gar Lepisosteus platostomus, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, and Flathead Catfish Pylodictis olivaris) across the Mississippi River, and test the hypothesis that microplastic counts in fish will increase from the headwaters to the mouth. Fish were sampled from several sites along the main-stem Mississippi River (from Minnesota to Louisiana). All four fish species had microplastics in their stomachs and downstream locations had higher microplastics concentrations; however, location had no significant effect on microplastic counts among species except for Largemouth Bass. Chapter two sought to quantify microplastics across body size in two common estuarine fish species, the Hardhead Catfish and Southern Flounder. Hardhead Catfish are benthic omnivores, and among one of the most common estuarine fishes in the Gulf of Mexico (but with almost no fishery value). Southern Flounder are an ambushing flatfish that inhabit estuaries at younger ages before a move offshore as adults. I hypothesized that microplastic concentrations in stomachs (and intestines) as measured by the number of microplastic particles in fish would be higher in smaller-sized fishes than larger-sized fishes (according to total length), as smaller fish target smaller prey and possibly directly ingest more microplastics. Fish were sampled in 2018 and 2019 within balanced size classes. Larger fish ingested more microplastics, which can be as a result of indirect consumption or accidental ingestion from the water column.

Committee Chair

Midway, Stephen