The impact of microplastic ingestion on gut microbial communities and their downstream health effects in a freshwater fish

Background/Question/Methods

Microplastics are a ubiquitous presence in the world’s aquatic environments. The Laurentian Great Lakes are one critical system affected by these pollutants. This system provides critical ecosystem services and economic opportunity for the region and understanding the impact microplastics have on these aquatic communities is vital. There is currently a large gap in our knowledge of how naturally weathered microplastics at ecologically relevant densities impact the health of aquatic species. To address this, we incubated microplastics in Muskegon Lake (Michigan), an Area of Concern, to evaluate how microplastic ingestion impacts the health of fathead minnows. Male and female fathead minnows were fed a diet of either food pellets (control), food pellets that included 4 polyethylene microplastic spheres (low density), or food pellets that included 16 polyethylene microplastic spheres (high density) per day for 28-days. Fecal samples were taken prior to treatment and then 28-days after feeding trials began, and gut tissue samples were taken post-treatment to assess gut microbial communities. We are evaluating whether ingestion of microplastics alters gut microbial communities via 16S amplicon sequencing. We are also exploring how ingestion impacts other health parameters, such as growth rates and hepatosomatic index.

Results/Conclusions

We found that ingestion of microplastics had significant impacts on some of the health parameters we evaluated, and these effects appear to be sex specific. Males from both the low density and high density treatments had significantly lower growth rates compared to control males. However, we did not observe this same effect on female growth rates. Ingestion of microplastics did not have a significant impact on hepatosomatic index for either sex. We are currently analyzing 16S amplicon sequencing data from the fecal samples and gut tissue to evaluate changes in gut microbial communities. While not a direct objective of this study, we also found that some of the microplastics were fragmented within the gut of individuals, which may be contributing to their breakdown within the environment. Together, this study integrates key issues of microplastic pollution and gastrointestinal microbiota to fully describe subtle, sublethal effects that are not currently understood in these aquatic systems.