Fish recently caught off the shores of Fukushima have shown the highest level of radioactive caesium detected in fish and shellfish caught in Japan since the Fukushima nuclear power plant disaster last year.

The fish were caught 12.5 miles off the plant on August 1 and registered 25,800 becquerels of caesium per kilo, Tokyo Electric Power Co. (TEPCO) said.

The amount is 258 times the level that the government has set for safe consumption.

The greenling fish may have fed in "radioactive hotspots", according to Agence France-Presse, but more samples of fish and seabed soil will be taken to measure patterns of radiation in the next few weeks.