A sailfish is a fish of the genus Istiophorus of billfish living in colder areas of all the seas of the earth. They are predominantly blue to gray in colour and have a characteristic erectile dorsal fin known as a sail, which often stretches the entire length of the back. Another notable characteristic is the elongated bill, resembling that of the swordfish and other marlins. They are, therefore, described as billfish in sport-fishing circles.
Two sailfish species have been recognized. No differences have been found in mtDNA, morphometrics or meristics between the two supposed species and most authorities now only recognized a single species, (Istiophorus platypterus), found in warmer oceans around the world.FishBase continues to recognize two species: