But prices of sushi are also soaring, no thanks to oil prices that have pinched supply by making fishing unprofitable for a third of the global long-line tuna fleet.

The fuel costs for so-called long- range tuna ships have doubled in a year, the Financial Times quoted Japan Tuna, an industry group, as saying. A fifth of Japans 360 ships may suspend fishing for four months from July. A further 140 ships in Taiwan, the mainland and South Korea have already decided not to fish, according to the Organization for the Promotion of Responsible Tuna Fisheries.

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The best tuna cuts are 25 percent more expensive. Prices have also been bolstered by a 20 percent drop in catches because of over-fishing, as well as by international quotas on the most valuable varieties such as the southern bluefin.