In rivers and reservoirs in Fukushima, scientists have identified the presence of fish with high levels of radiactive cesium.
Among the specimens with the highest levels of the contaminant was a mountain trout with 11,400 becquerels of cesium per kg, more than 100 times the limit of 100 becquerels per kg established in Japan.
The trout was caught in the Niida river in the city of Minamisoma, 20 km north of the Fukushima Daiichi plant.
Last year's detection of radioactively contaminated rice and beef following the nuclear disaster set off by the 2011 earthquake and tsunami led the government to reduce in April the level allowed for fruit, vegetables, cereals, fish, seafood and meat from 500 to 100 becquerels.
Similarly, the limit for milk and baby food was reduced from 200 to 50 becquerels of cesium per kg, and from 200 to 10 for water.
The study was taken last June and July to analyze cesium levels in fish and insects in rivers, lakes and coastal waters of the province.
The accident at the Fukushima Daiichi plant, caused by the earthquake and tsunami that devastated the northeastern part of the country in 2011, was worse than the one at Chernobyl in 1986, and some 52,000 people from within a radius of 20 km were evacuated from their homes.