KOSAKA Sushi Otoro (Fatty Tuna) (2)-2
O-toro (fatty tuna) at NYC’s Kosaka. Farm-raised tuna can have excess fattiness to it due to the fish’s diet.

More than any other type of cuisine, sushi can be an especially subjective meal. A wide range of fish — much of which is prepared raw and some of which is largely foreign to the American palate — ensures that dinner at a sushi restaurant is often a novel experience no matter how adventurous the diner. But even the simplest offerings can have quite the story behind them.

Take tuna (maguro), for example. Viewed as the basic cornerstone of any sushi or sashimi platter and as the most common ingredient in maki rolls, you might think high-end establishments would have a set routine when it comes to ordering the red-hued fish from their suppliers. But it turns out that this is not the case. On the contrary, three NYC chefs we spoke to from upscale Japanese restaurants expressed a preference for experimenting with their tuna deliveries, based primarily on seasonality. And we’re not even getting into the whole global fish-mislabeling epidemic here.

Sushi Ginza Onodera Bluefin Tuna
Sushi Ginza Onodera uses only wild-caught tuna from all regions of Japan as part of its sushi offerings.

Chef Masaki Saito of the city’s branch of omakase­-only mecca Sushi Ginza Onodera imports all his cuts of bluefin tuna from Japan. “Because tuna migrate, their flavor changes over seasons,” he explains. He most frequently imports maguro from both the north and south of Japan — every 10 to 14 days, on average — and always chooses wild-caught over farm-raised (as with the majority of its fish). His reasoning is simple: “Wild-caught fish taste better,” he says. But that’s certainly not the consensus among sushi chefs.

Chef Yoshi Kousaka of West Village omakase restaurant Kosaka agrees that it all depends on the season, though he has shown more of a willingness to expand his horizons beyond Japan. He says he uses wild-caught bluefin tuna from Boston from August until around December. In the winter season, he uses farm-raised tuna from Spain, Italy, Turkey and Mexico. Chef Masashi Ito of pristine omakase ­spot Sushi Zo in Greenwich Village has previously mentioned his affinity for farm-raised tuna to us, though it is all imported from Japan on a weekly or biweekly basis.

Sushi Zo uses Japanese farm-raised tuna, which can change color quickly.

So what exactly is the deal with farm-raised tuna? Though Kousaka mentions that the color of farm-raised tuna changes very quickly and can make it difficult to handle as a chef, he describes the Spanish variety as top quality. “There was a Japanese person who went [to Spain] to train the people there,” he explains. Besides the color, there is another difference between the two. “Farm-raised tuna can be too fatty, and even lean tuna can have an excess fattiness,” elaborates Kousaka. “The fat is sometimes unpleasant.” This extra weight is most likely attributed to the diet that the fish are fed (or, more often than not, overfed).

And there you have it. The next time you dine out at a sushi restaurant, don’t be afraid to ask about the source of your tuna. The answer just might surprise you — and have slightly more of a backstory than you may expect.