Tuna are several species of ocean-dwelling carnivorous fish in the family Scombridae, mostly in the genus Thunnus. Tunas are very fast swimmers—they have been clocked at 70 km/h (45 mph)—and include several species that are warm-blooded.
Unlike most fish species, which have white flesh, tuna have flesh that is pink to dark red. The red coloring comes from tuna muscle tissue's greater quantities of myoglobin, an oxygen-binding molecule. Some of the larger tuna species, such as the bluefin tuna, can raise their blood temperature above that of the water through muscular activity. This ability enables them to live in cooler waters and to survive in a wide range of ocean environments.
Nutrition and health
Canned tuna is a prominent component in many weight trainers' diets, as it is very high in protein and is easily prepared.
Tuna is an oily fish, and therefore contains a high amount of Vitamin D. A can of tuna in oil contains about the Adequate Intake (AI) of the US Dietary Reference Intake of vitamin D for infants, children, men, and women aged 19–50 - 200 UI.
Canned tuna can also be a good source of omega-3 fatty acids, of which it sometimes contains over 300 mg per serving.