Pacific Bluefin tuna caught off the coast of California have been found to have radioactive contamination from last year's Fukushima nuclear accident.
The fish would have picked up the pollution while swimming in Japanese waters, before then moving to the far side of the ocean.
Scientists stress that the fish are still perfectly safe to eat.
However, the case does illustrate how migratory species can carry pollution over vast distances, they say.
"It's a lesson to us in how interconnected eco-regions can be, even when they may be separated by thousands of miles," Nicholas Fisher, a professor of marine sciences at Stony Brook University, New York, told BBC News.
Fisher and colleagues report their study in the journal Proceedings of the National Academy of Sciences.
They examined the muscle tissues of 15 Bluefin tuna (Thunnus orientalis) taken from waters off San Diego in August 2011, just a few months after the accident at the Fukushima Daiichi nuclear plant. Read More