Who would know from looking at a cheap can of tuna that it was made from one of the most remarkable fish on earth? The tunas are large predators of the open ocean, reaching 1,500 lb/680 kg and swimming constantly at speeds up to 40 miles/70 km per hour. Even their fast-twitch muscle fibers, which are normally white and bland, contribute to the nonstop cruising, and have a high capacity for using oxygen, a high content of oxygen-storing myoglobin pigment, and active enzymes for generating energy from both fat and protein. This is why tuna flesh can look as dark red as beef, and has a similarly rich, savory flavor. The meaty aroma of cooked and canned tuna comes in part from a reaction between the sugar ribose and the sulfur-containing amino acid cysteine, probably from the myoglobin pigment, which produces an aroma compound that’s also typical of cooked beef.