Radioactive cesium measuring 258 times the amount that Japan's government deems safe for consumption has been found in fish near the damaged Fukushima Daiichi nuclear power plant, Japan's Kyodo news agency reported Tuesday.

The Tokyo Electric Power Co. found 25,800 becquerels per kilogram of radioactive cesium in two greenlings in the sea within 20 kilometers of the plant on August 1 - a record for the thousands of Fukushima-area fish caught and tested since the March 2011 earthquake and tsunami that led to a nuclear disaster at the plant, Kyodo reported.

Japan's government considers fish with more than 100 becquerels per kilogram unsafe for consumption. A becquerel is a measurement of radioactive intensity.

TEPCO said it also found limit-exceeding radioactive cesium levels in several other kinds of fish and shellfish during the testing, which happened in the Fukushima area from mid-July to early August, according to Japanese broadcaster NHK.

The finding comes 17 months after the disaster at the plant, which spewed radiation and displaced tens of thousands of residents from the surrounding area. It was the worst nuclear accident since the 1986 Chernobyl disaster in Ukraine.

News of the finding also comes after scientists reported finding mutant butterflies - with abnormalities in their legs, antennae and abdomens, and dents in their eyes - in and around Fukushima prefecture in the months after the nuclear disaster.

The previous post-disaster radiation record in fish - 18,700 becquerels per kilogram, or 187 times the government's limit - was found in landlocked salmon in Iidate village, Fukushima prefecture, on March 18, according to Japan's fisheries agency, which has conducted its own tests in conjunction with local governments.

Japan's government has restricted fishing in the Fukushima area since the disaster. However, fishing for two kinds of octopus and one kind of shellfish has happened on a trial basis more than 50 kilometers outside the plant since June, NHK reported.

The vast majority of the thousands of fish tested since the disaster are within the government's radioactive cesium limit, according to the fisheries agency.

TEPCO plans to do more testing - of rock trout, their prey and mud from the seabed - in August and September, NHK reported.

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