Fish
Black Marlin
Istiompax indica · also called black marlins
A black marlin is built for pure speed, considered one of the fastest fish in the entire ocean, and part of what sets it apart physically is something it cannot do: fold its pectoral fins flat the way nearly every other marlin species can. Those fins stay rigidly fixed in place, a genuinely unusual trait for a billfish this fast.
Overview
The black marlin, Istiompax indica, is a large, powerful billfish of the tropical and subtropical Indian and Pacific Oceans. A long, spear-like bill slashes at schooling prey to stun it before the marlin circles back to feed, and rigid pectoral fins mark it apart from related marlin species.
Speed, size, and a prized catch
Among the fastest fish known, with females growing considerably larger than males, the black marlin’s power and acrobatic fight once hooked have made it a top target in big-game sport fishing across the Pacific and Indian Oceans.
Status
Data Deficient — its wide-ranging, highly migratory open-ocean lifestyle makes comprehensive population surveys difficult, leaving real uncertainty about its total numbers despite ongoing fishing pressure.
Black Marlin: common questions
Why can't a black marlin fold its pectoral fins flat like other marlin?
The black marlin's pectoral fins are structurally rigid and fixed in position, unlike the more flexible pectoral fins of most other billfish species, which can be folded down against the body to reduce drag while swimming, and this distinctive anatomical difference is one of the clearest and most reliable physical features used to identify a black marlin and distinguish it from closely related marlin species.
How fast can a black marlin actually swim?
The black marlin is considered one of the fastest fish species in the ocean, capable of very high burst swimming speeds supported by its streamlined body and powerful swimming muscles, allowing it to pursue and capture fast-moving prey effectively and also making it an especially challenging and exciting species for recreational anglers once hooked.
Why don't researchers know more about black marlin population numbers?
Black marlin are wide-ranging, highly migratory open-ocean fish that are difficult and expensive to survey comprehensively across their full range in the Indian and Pacific Oceans, and much of the available data on the species comes from fisheries bycatch records and recreational catch reports rather than dedicated, comprehensive population surveys, which together contribute to the significant uncertainty reflected in its current Data Deficient conservation status.
Does a black marlin actually use its bill to stab prey?
The bill is generally used to slash at and stun schooling prey fish through rapid sideways or slashing movements rather than a direct stabbing motion, and after successfully stunning or injuring prey in this way, the marlin will typically circle back to consume the disabled fish, making the bill an effective hunting tool rather than simply a passive physical feature.