Tokyo Electric Power Company Holdings Inc (Tepco) said on Monday that  black rockfish living near drainage outlets at the nuclear plant which was caught on May 18 had 18,000 becquerels per kilogram of cesium-137, compared with the legal maximum level of 100 becquerels per kilogram.

The company also confirmed that a total of 44 fish with cesium levels above 100 becquerels per kg have been found in the Fukushima plant port between May 2022 and May 2023, with 90 percent of those caught in or near the inner breakwater.  

It said rainwater from the areas around reactors one, two and three, which melted down during the 2011 disaster, flows into the inner breakwater where the rockfish was caught in May.

According to Tepco, cesium concentration in the sediment from the seabed in the inner breakwater measures more than 100,000 becquerels per kg.

"Since contaminated water flowed into the Fukushima Daiichi nuclear power station port immediately after the accident, Tepco has periodically removed fish from inside the port since 2012 using fishnets that have been installed to prevent the fish from escaping the port," the company said.

Regular monitoring of fish from the inner breakwater had been suspended after nets were installed in January 2016 to keep potentially contaminated fish inside the area.

However, Tepco said, "when a black rockfish with radioactive concentrations that exceed regulatory standards was caught off the coast of Soma [about 50km north of the plant] in January 2022, we began sampling again within this area in conjunction with the installation of more nets to prevent fish from leaving the port."