Low levels of nuclear radiation from the tsunami-damaged Fukushima power plant have turned up in bluefin tuna off the California coast.

Researchers believe the young fishes left Japanese water about a month after the accident.

The Japanese government said it is looking into the international monitoring of radioactive fish products, but more information is needed.

(SOUNDBITE) (Japanese) JAPANESE CABINET SECRETARY OSAMU FUJIMURA SAYING:

"We haven't really got hold of the research paper on this migrant tuna fish off the southern coast of California yet. We expect that we will have to deal with the issue of monitoring international fish product supplies, but we need to gather more information before looking at how to deal with this issue."

Small amount of cesium-137 and cesium-134 were detected in 15 tuna caught near San Diego in August last year.

The amount is not thought to be damaging to people if consumed.

Most of the radiation was released over a few days in April 2011.

Unlike some other compounds, radioactive cesium does not quickly sink to the sea bottom but remains dispersed in the water.

Sophia Soo, Reuters.