A marlin is a fish from the family Istiophoridae, which includes about 10 species. It has an elongated body, a spear-like snout or bill, and a long, rigid dorsal fin which extends forward to form a crest. Its common name is thought to derive from its resemblance to a sailor's marlinspike. Marlins are among the fastest marine swimmers, reaching ~110 km/h (68 mph) in short bursts. However, greatly exaggerated speeds are often claimed in popular literature, based on unreliable or outdated reports. Swordfish (Xiphias gladius), also known as broadbills in some countries, are large, highly migratory, predatory fish characterized by a long, flat, pointed bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood.