Kazuhiro Ukiuchi loves his tuna sushi, and he tries to have it once a week — despite the common knowledge in Japan the popular fish can contain toxic mercury.

"I wouldn't worry about it," Ukiuchi said, strolling through Tokyo's main fish market on Friday. "We're not talking about eating 10 tuna sushi every day — in which case I might be a little bit worried."

Recent reports in the United States about high levels of mercury in tuna served at ubiquitous sushi restaurants in New York have been met with a collective yawn in Japan, the world's undisputed sushi capital.