Tuna is a type of fish that belongs to the family Scombridae, which includes other species such as mackerel and bonito. There are many different varieties of tuna found in warm waters around the world, including the Atlantic bluefin tuna, yellowfin tuna, albacore tuna, bigeye tuna, and skipjack tuna. Tunas are fast swimming fish that can reach speeds of up to 40 miles per hour, making them one of the fastest species in the ocean. They have a streamlined body shape with a dorsal fin on their backs and a forked tail. Tuna is also used as a common name for several other species of fish that are not technically tunas but share similar characteristics such as salmon, mackerel or sardines.