The Influence of Polystyrene Microplastics on Juvenile Steelhead Trout (Oncorhynchus mykiss)

Mass production of plastic within the past decade has led to over 100 billion tons of plastics being added to the world’s oceans through rivers and effluent disposal and decomposition. For marine environments, the sudden and constant growth of microplastics (plastics 1 µm to 5 mm in diameter), is of particular concern to top-predatory fish such as steelhead trout (Oncorhynchus mykiss), who passively or actively uptake microplastics while consuming prey. Previous research has demonstrated clear detrimental impacts of microplastic accumulation in bivalves, seabirds, and zebrafish, including decreased diet, reproduction rates, and metabolism, as well as increased rates of mortality. However, research in large commercial fish such as steelhead trout is lacking. As steelhead trout are top-predatory anadromous fish, they are particularly susceptible to microplastic exposure through their interaction with widespread ecosystems and the bioaccumulation of microplastics during food consumption throughout their lifetime. Here, we demonstrate how polystyrene microplastics affect juvenile steelhead trout behavior, intestinal tissues, and oxidative stress levels. Our study illustrates microplastic exposure in trout could lead to rapid die offs after acute periods of high exposure. Additionally, we found that even at low levels of polystyrene exposure (10µg/L) results in behavioral modifications, intestinal tissue damages, and increases in oxidative stress. More broadly, our results demonstrate that microplastic exposure causes negative responses in large commercial fish, with potential to alter species survivability and ecosystem dynamics in both wild and farmed populations.