Sushi isn’t purely Japanese, even in its origins. Nothing could be more associated with Japanese fish consumption, at least by American gourmands, than the worship of fatty tuna belly, or otoro. But, says Issenberg, “Tuna was worthless to the Japanese — especially the fatty cuts that are now the most prized — until the postwar period.” It was the American occupation that inspired the rise of tuna, via our appetite for red meat, never a part of the Japanese diet.
Sushi chefs may well have no idea where the fish they are cutting came from. Issenberg: “Fish often passes through so many hands before it gets to you, even a well-meaning chef might not know where his fish came from — what country, which ocean, how long it's been out of water, if it's fresh, if it's been frozen at all.”
Sushi isn’t even necessarily made from fresh fish. Most of the sushi in America has been frozen in giant liquid-nitrogen coolers, and although “we’ve come to think that the freshest tuna is the ultimate sushi experience,” Corson says, “if you go back and order a piece of mackerel sushi that's pickled, that's the technique that originally defined sushi.” Eating it raw far from where it was caught, Issenberg notes, means that “sushi is now operating diametrically opposed to where it started.” Sushi was originally meant to be eaten as a preserved food.
Fish Tales [Slate]