Sailfish

The sailfish is one of two species of marine fish in the genus Istiophorus, which belong to the family Istiophoridae . They are predominantly blue to gray in colour and have a characteristically large dorsal fin known as the sail, which often stretches the entire length of the back. Another notable characteristic is the elongated rostrum (bill) consistent with that of other marlins and the swordfish, which together constitute what are known as billfish in sport fishing circles. Sailfish live in colder pelagic waters of all Earth's oceans, and hold the record for the highest speed of any marine animal. There is a dispute based on the taxonomy of the sailfish, and either one or two species have been recognized. No differences have been found in mtDNA, morphometrics or meristics between the two supposed species and most authorities now only recognize a single species, Istiophorus platypterus, found in warmer oceans around the world. FishBase continues to recognize two species:

Source: Wikipedia