|Tuna's are also called
Tunny. They are related to mackerels and are commonly placed with them
in the family Scombridae (order Perciformes). Tunas vary considerably,
both within and among species. Their classification is also variable and
may differ from one authority to another. Another notable feature is a
well-developed network of blood vessels below the skin that acts as a
temperature-regulating device associated with long-term, slow swimming.
Owing to this vascular system, tunas are unique among fishes in their
ability to maintain the temperature of their bodies above that of the
surrounding water, sometimes by as much as 14° C (20° F). Tunas
migrate long distances over all the world's oceans and occupy tropical,
temperate, and even some cooler waters. Tunas feed on fishes, squid, shellfish,
and a variety of planktonic organisms. They spawn in the open sea over
very large areas. The canned meat of albacore and yellowfin tunas is one
of the world's most popular fish foods.