A wholesaler fillets a tuna at the Tsukiji fish market in Tokyo in a file photo. Japanese researchers are looking for ways to reduce stress levels in tuna caught in nearby waters, so they taste better when they hit the plate. REUTERS/Kiyoshi Ota

TOKYO (Reuters) - Japanese researchers are looking for ways to reduce stress levels in tuna caught in nearby waters, so they taste better when they hit the plate.

A vigorous fish, tuna tends to thrash wildly when caught, which researchers believe raises its body temperature and leads to whitening of its meat, sharply cutting its flavor and value.

“People want to eat tuna when it’s as fresh as possible, but once it struggles the freshness goes down,” said Kunihiko Konno, a professor at Hokkaido University who is leading the stress-reduction project.

Tuna tend to struggle especially hard if too many are trapped in a net at once or if they are kept in crowded conditions at fish farms, but the researchers are focusing mainly on how to reduce stress when the fish are caught, he added.

Although they have yet to reach firm conclusions, Konno said the best way to reduce stress levels was likely to be quite simple -- and final.

“Kill them very quickly,” he said.