“We purposely deep-freeze at negative 83 degrees, and we use one of those medical cryogenic freezers,” said Yuta Suzuki, vice president of Sushi Zen, a popular Times Square restaurant. “This way, it’s kind of like cooking, but instead of using heat we use freezing to remove parasites or bacteria on the outer surface.”

Even the New York City chapter of the New York State Restaurant Association, which had complained about the regulations at a health department hearing in January, has reversed course. Now that the regulations have been stripped of certain record-keeping requirements that the association considered onerous, establishments serving raw fish should be able to handle the change, James W. Versocki, a legal counselor for the group, said.

“By all indications, everyone will be enjoying the same quality of sushi,” Mr. Versocki said, who noted that the vast majority of fish is already flash frozen at some point in the supply chain.

The websites and menus for some of the city’s most expensive restaurants are often masterpieces of obfuscation when it comes to the word “fresh.” Even at Masa, which touts ingredients “only in their freshest most delicious state” for its $450 meals, chef Masayoshi Takayama has been known to occasionally opt for frozen fish. Naomichi Yasuda, whose restaurant, Sushi Yasuda, consistently ranks among the city’s best, has been extolling the merits of freezing fish for years. Not only does frozen fish come free of parasites, it is also cheaper, available out of season, and, in some cases, tastier. Plus, most diners are none the wiser.

“I’m pretty sure our customers are not able to tell,” Mr. Suzuki said, who noted that Sushi Zen doesn’t keep any of its fish raw.