The black marlin (Istiompax indica) is a species of marlin found in tropical and subtropical areas of the Indian and Pacific Oceans. With a maximum published length of 4.65 m (15.3 ft) and weight of 750 kg (1,650 lb), it is one of the largest marlins and also one of the largest bony fish. It is one of the fastest fish species as well, having been recorded unwinding fishing line at 129 km/h (80 mph). Black marlin are fished commercially and are also a highly prized game fish.
Compared to striped or white marlins and sailfish, black marlins are more solid than their blue counterparts. They have a shorter bill and a rounder and lower dorsal fin. Black marlin may be distinguished from all other marlin species by their rigid pectoral fins, which, especially from a weight of around 150 lb (75 kg) or so, are unable to be pressed flat against their sides.
According to wikipedia