The Indo-Pacific sailfish (Istiophorus platypterus) is a sailfish native to the Indian and Pacific Oceans. It is dark blue on top, brown-blue laterally, silvery white underbelly; upper jaw elongated in the form of a spear; first dorsal fin greatly enlarged in the form of a sail, with many black cones, its front squared off, highest at its midpoint; pelvic fins very narrow, reaching almost to the anus; body covered with embedded scales, blunt at end; lateral line curved above pectoral fin, then straight to base of tail. They have a large and sharp bill, which they use for hunting. They feed on tuna and mackerel, some of the fastest fish in the Ocean. They are able to prey on the faster fish in the sea because their top speed has been clocked at 109 km/h (68 mph), making them one of the fastest fish in the ocean. The Indo-pacific sailfish is related to the marlin.
It is theorized by marine biologists that the 'sail' (dorsal fin array) of the sailfish may serve the purpose of a cooling and heating system for this fish; this due to a network of a large number of blood vessels found in the sail and because of "sail-raising" behaviour exhibited by the sailfish at or near the surface waters after or before high-speed bursts.