Fukushima Dai-ichi Nuclear Power Plant Accident's Lingering Impacts on Freshwater Fish

Freshwater fishing activities remain restricted in some Japanese rivers and lakes due to the persistence of cesium-137 (Cs) contamination. The Japan Fisheries Research and Education Agency has conducted research on the effects of Cs on the ayu fish species, which feeds on periphytic algae and fine sediments. The study found that despite whole-body monitoring, it is challenging to ascertain the Cs concentration in the ayu fish body, as it is affected by Cs in fine sediments. To gain an accurate assessment, the researchers removed refractory portions affecting the whole-body Cs concentration and measured Cs concentrations in muscle, head, and internal organs. The study concluded that the procedure for monitoring Cs in ayu fish should be reviewed due to the significant impact of Cs on the species.

Key Takeaways:

• The Fukushima Dai-ichi Nuclear Power Plant accident in 2011 released large amounts of Cs into the atmosphere, which deposited on land, especially in Fukushima Prefecture, Japan.
• Freshwater fish in Fukushima Prefecture contain high levels of Cs, leading to fishing restrictions in some rivers and lakes.
• The ayu fish species is affected by Cs contamination, with 18.0% of specimens exhibiting whole-body Cs concentrations exceeding the Japanese regulatory limit in May 2022.
• In October 2022, 50.0% of ayu fish specimens showed whole-body Cs concentrations exceeding the limit, whereas none of the specimens exceeded the limit when refractory portions were removed.
• The study suggests that the current procedure for monitoring Cs in ayu fish is inadequate and should be reviewed to ensure accurate assessments of Cs contamination.
• The research has significant implications for freshwater fish management and conservation in Japan, particularly in areas affected by the Fukushima Dai-ichi Nuclear Power Plant accident.

Statistics:

• 18.0% of ayu fish specimens in May 2022 had whole-body Cs concentrations exceeding the Japanese regulatory limit (May 2022).
• 50.0% of ayu fish specimens in October 2022 had whole-body Cs concentrations exceeding the Japanese regulatory limit (October 2022).
• Cs contamination has been a persistent issue in Fukushima Prefecture for over a decade since the Fukushima Dai-ichi Nuclear Power Plant accident in 2011 (2011).
• The study highlights the importance of accurate monitoring and assessment of Cs contamination in freshwater fish populations in Japan (2025).

Sources:

• Assessment of the cesium-137 concentration in algae-grazing ayu Plecoglossus altivelis collected from Tomioka River in Fukushima, Japan (2025)
• Journal of Environmental Radioactivity, Elsevier Sci Ltd (www.elsevier.com; www.journals.elsevier.com/journal-of-environmental-radioactivity/)
• Japan Fisheries Research and Education Agency, Yokohama, Kanagawa, 236-8648, Japan (Takami Morita, contact information)