Sushi aficionados: when you were tucking into morsels of sushi draped over with marbled slabs of sliced otoro or chu-toro, has it ever occurred to you if the prized fish in question were wild-caught or farmed tuna?
Perhaps you were unable to discern the difference between farmed and wild tuna. But according to Tomoo Kimura, Chef-Owner of the 12-seat Sushi Kimura in Singapore, the difference between the two is like “glass and diamond”.
“Wild tuna can range in size from 70 kg for a five-year-old to over 300 kg for a fish older than 20 years old,” says Kimura, who generally uses wild blue fin tuna with a weight range of 200 kg to 300 kg. “But farmed tuna tends to be about three years.”
He adds that farms have the practice of fattening tuna with feed until the age of about three, an age perceived by farms to be most profitable for tuna farming, when the fish reaches a maximum weight of 70 kg. “Wild blue-fin tuna reaches a weight of 50 kg in about three years but farmed tuna reaches 70 kg within the same period."
While there is no seasonality for farmed tuna, Kimura says that the best season for wild Pacific tuna is from December to January at the Aomori prefecture and around the Hokkaido area where the fish is at its fattest. “The current in the Aomori and Hokkaido area is very cold during this time, therefore the Pacific blue-fin tuna sourced from here has more fat,” says Kimura. “Aomori also has one of the best squids during winter and these wild blue-fin tuna feeds on them.”
The chef also says that before the tuna-mating season starts from February to May period, the Pacific blue-fin tuna’s body changes energy to yield better-tasting flesh, further explaining why wild Pacific blue-fin tuna is best in winter, before February. “During the off-season of February to May, usually we use frozen Irish or Boston tuna as well as farmed tuna.”
The best season for Atlantic tuna is from September to October.
Kimura says that visually, farmed tuna is pinkish (“slightly whiter than wild tuna”) while wild tuna bears a bold vivid red especially when exposed to air.
On the palate, the difference between the two is even more distinct. “Farmed tuna is fed a fat and protein-rich diet that includes non-seafood, which yields flesh that tastes fishy with little flavour or umami,” says Kimura, who likens the mouth feel of eating farmed tuna to adding mayonnaise to one’s food. “Its fat texture is watery and even the leaner cut of tuna feels fatty.”
Wild tuna, on the other hand, feeds in the wild on sea creatures like squid and sardines, he says, hence it has a distinct “fish blood” flavour that Kimura associates with “rich wine flavour” that is “not fishy” with “refined fat”.
Kimura also highlights the difference in the landed price of farmed and wild blue-fin tuna.
“Wild blue-fin is more expensive, about two to three times more than farmed tuna of the same size, because its supply is reduced and there isn’t sufficient supply to meet demand.”
The Japanese chef who hails from Tokyo concedes that in future, perhaps in 20 to 30 years, farmed tuna will taste better than the wild ones as tuna farmers gain more experience. Until then, wild tuna will still fetch a massive premium over farmed ones with overfishing and a dwindling stock globally.