Perhaps the most iconic of endangered fish, the bluefin tuna occupies most of the northern Atlantic Ocean. One of the fastest fish in the sea, this species can grow to a length of 10 feet and weigh more than 1,400 pounds. This species' reputation as a fighter has made it a popular catch among recreational fisherman. And at a going rate of up to $100,000 per fish, it's highly prized by commercial fisherman as well. Bluefin tuna are heavily overfished, and most experts agree that without prompt intervention, the slow-growing, slow-maturing species will become extinct. International regulation is tricky, however, since the bluefin tuna is known to migrate thousands of miles across the ocean. And so far, efforts to control harvests have largely failed. Chosen by the WWF (formerly known as the World Wildlife Fund) as the sixth most threatened species in the world, sea or land, the bluefin tuna is by all measures critically endangered.