Sushi is more popular than ever before but eating it "has become the new Russian roulette" in terms of safety, a group campaigning against mercury in fish said.

Eli Saddler of gotmercury.org, a campaign of California-based Sea Turtle Restoration Project, went to six top sushi restaurants in Los Angeles to test mercury levels in the fish they serve.

"The level of mercury in tuna these restaurants serve is so high they should be keeping this food off their lists," Saddler said. "Eating sushi has become the new Russian roulette."

Gotmercury.org proposes to take the study to various cities across the United States and educate sushi consumers on the risks of mercury intake, which can permanently damage the nervous system in fetuses and may cause temporary memory loss in adults.

Tuna samples from six popular sushi restaurants in Los Angeles were taken to a Southern California lab for testing.

They returned an average mercury level of 0.721 parts per million, about 88 percent higher than the reported Food and Drug Administration level of 0.383 ppm for all fresh and frozen tuna.

A couple of samples had mercury levels the FDA has declared "unsafe for anyone to eat," Saddler said.

Big-eyed tuna and blue and yellow-finned tuna are the most popular varieties used in sushi restaurants. Older and bigger fish are considered best suited for sushi but Saddler said it was not widely known that fish with longer lives carry more mercury than others.

Studies show seafood like shrimp and salmon with short life spans pose almost no risk of carrying mercury.

Nobi Kusuhara, owner of Sushi Sasabune in Los Angeles said even though the mercury level in the samples was higher than he expected, sushi is still healthy to eat.

"Even in Japan we have warnings out like FDA has issued here," Kusuhara said. "As long as restaurants warn pregnant women and people to eat smaller fish, it is definitely safer and healthier than beef or chicken."

Businesses with more than 10 employees are bound under California law to post a mercury-in-seafood warning if they serve or sell any seafood.

But Saddler said that, of the six restaurants checked, only one had an explicit sign posted on the door.

"There are cheap and easy ways to test fish, so it should be done in the United States to protect sushi consumers," Saddler said.