There are three closely related types of Bluefin Tuna - the Pacific (Thunnus orientalis), Atlantic (Thunnus thynnus) and Southern (Thunnus maccoyii), each inhabiting waters designated by their name. As other Tuna fish, chilly seas pose no problem - their highly developed thermoregulatory system allows for keeping their body temperature up to 36°F warmer than the surrounding water, which not only means they can thrive in great geographical latitudes, but in great depths as well. Not losing heat through their gills also dramatically adds to their stamina, making them extremely fast (can swim up to 40mph) and endurant (Gordon Johnson speaks about a 62 hour long fight in his book, "It Happened in Canada") predators.
An interesting fact about red-flesh fish is that their meat was regarded as a low class food in Japan before refrigeration was invented, as it was basically impossible to conserve. The popularity of sushi, however, brought the Bluefin Tuna to a meat value pedestal, culminating in 2013 with a $1.76M purchase of a single 489lbs fish at the Tsukiji fish market in Tokyo