Toro is the fatty underbelly of he northern bluefin tuna.  The northern bluefin tuna is an important source of seafood, providing most of the tuna used in sushi. It is a particular delicacy in Japan where at one auction, a single giant tuna sold for more than $100,000 on the Tsukiji fish market in Tokyo. It is also popular in Taiwan, particularly in the town of Tungkang. As a result, some fisheries of bluefin are considered overfished, and this problem is compounded by the bluefin's slow growth rate and late maturity. The Atlantic population of the species has declined by nearly 90 percent since the 1970s. The bluefin species are consequently listed as ones to "Avoid" on the Monterey Bay Aquarium Seafood Watch program.

To supply sushi markets, the bluefin tuna is reported to be fished at 4 times the sustainable rate. Numerous ranches across Mediterranean harvest juvenile Bluefin indiscriminately fattening them offshore to improve the quality of meat. The industry is worth 220 million dollars a year. Each female produces 40 million eggs and these bluefin ranches pose a serious risk to the population of bluefin in the seas, by wiping them out at all stages of their life cycle.