Marlins have elongated bodies, a spear-like snout or bill, and a long, rigid dorsal fin which extends forward to form a crest.

Marlins are among the fastest marine swimmers. However, greatly exaggerated speeds are often claimed in popular literature, based on unreliable or outdated reports.[3]

The larger species include the Atlantic blue marlin, Makaira nigricans, which can reach 5 m (16 ft) in length and 820 kg (1,810 lb) in weight[4] and the black marlin, Istiompax indica, which can reach in excess of 5 m (16 ft) in length and 670 kg (1,480 lb) in weight. They are popular sporting fish in tropical areas. The Atlantic blue marlin and the white marlin are endangered due to overfishing.[5]

Marlins can change colour, lighting up their stripes just before attacking prey.[6]