Microplastics are synthetic polymers that are less than 5mm in diameter that can be ingested by aquatic organisms accidentally or purposely if they mistake them for food, which has been demonstrated in several studies. It is believed that this consumption results from visual or tactile misidentification; especially if the plastic is of similar size and color as its typical prey. To test this hypothesis, two age classes of fathead minnows (<i>Pimephales</i> <i>promelas</i>), a one-month old (n=20) and three-month old (n=30), were observed individually in a 19x11.5cm arena with similar looking microbeads and food using a three-dimensional behavior tracking system (EthoVision) to test for favorability of one material over the other. We divided the EthoVision arena into three sections (Food Zone, Neutral Zone, and Microbead Zone), and counted the amount of time each fish spent in each zone throughout the 90 second trials. Both age classes were found to favor their food over the microbeads (1-month p-value of 0.002; 3-month p-value of &lt;0.0001); however, the older age class exhibited higher favorability for food. The favorability of food over microplastics of similar size, shape, and color leads to the possibility that olfaction might play a role in selective ingestion by fathead minnows. The results of our study support the notion that the sense of smell in fish gets stronger with age and/or fish have the ability to learn. Although it cannot be assumed all fish species can distinguish microplastics from food, these results add to our understanding of the complexity of fish microplastic ingestion.

Fatheads don’t eat plastic: Food preference among juvenile fathead minnows

ACS Spring Meeting 2021

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