The impacts of microplastic pollution on freshwater fishes in Japan's Komaoi River and Tama River

In recent years, environmental pollution caused by microplastics (MP) has become a global issue, yet only a few studies have considered MP pollution of freshwater fish, in contrast to the substantial research done on seawater fish. Thus, the purpose of this study is to examine MP pollution of river fish. To this end, we obtained Ayu (Plecoglossus altivelis) from Tama River Tokyo and Ugui (Tribolodon Hakonensis) from Komaoi River, Hokkaido. We also collected MP samples from the river water in both locations in order to examine the relationships of MP pollution between fishes and river water. Our findings were as follows. In the Komaoi River, MPs were detected in 2 out of 8 Ugui with 0.25 particles on average and up to 1 particle per individual. In the Tama River, MPs were detected in 2 out of 2 Ayu with 4 particles on average and up to 4 particles per individual. Thus, the MP pollution in the Ayu was higher than in the Ugui. In addition, the MP numerical concentrations in the Tama and Komaoi Rivers were 3.75 and 0.50 particles/m³, respectively. Together, these facts show that the MP pollution in the Tama River was greater than that in the Komaoi River and consequently had a greater tendency within its fish.