The Blue Marlin (Istiophoridae) is a species of fish found in Atlantic waters. They are characterized by an elongated body, a long dorsal fin, and a rounded spear extending from the snout. They are wanderers, found worldwide near the surface of the sea, and are carnivorous, feeding largely on other fishes. They are consumed as food and are highly prized by sports fishermen.
The Atlantic blue marlin (hereafter, blue marlin) feeds on a wide variety of organisms near the surface. It uses its bill to stun, injure, or kill while knifing through a school of fish or other prey, then returns to eat the injured or stunned fish. Marlin is a popular game fish. The relatively high-fat content of its meat makes it commercially valuable in certain markets. It is the national fish of the Commonwealth of the Bahamas and is featured on its coat of arms.
The marlin has two dorsal fins and two back fins. The fins are supported by bony spines known as rays. Its first dorsal fin has 39 to 43 rays from front to back. Its second dorsal fin has six or seven rays. Its first back fin, which is similar in shape and size to the second dorsal fin, has 13 to 16 rays, and the second back fin has six or seven rays. The pectoral fins, which have 19 to 22 rays, are long and narrow and can be drawn into the sides of the body. The pelvic fins are shorter than the pectorals, have a poorly developed membrane, and are depressible into ventral grooves. Its first back fin, along with its pectoral and caudal fins, can be folded into grooves. This streamlines the fish and thereby reduces drag. Blue marlin, like other billfish, can rapidly change color, an effect created by pigment-containing iridophores and light-reflecting skin cells. Most often, however, the body is blue-black on top with a silvery white underside. It has about 15 rows of pale, cobalt-colored stripes, each of which has round dots and/or thin bars, located on both sides of the fish. The first dorsal fin membrane is dark blue or almost black and has no dots or marks. Other fins are normally brownish-black, sometimes with a hint of dark blue. The bases of the first and second back fins have a hint of silvery white.
Adult blue marlin have few predators apart from killer whales, sharks, and humans. They are sought after as a highly prized game fish by anglers and are taken by commercial fishermen, both as a directed catch and as bycatch in major industrial tuna fisheries. According to the IUCN, blue marlin is currently considered a threatened species due to overfishing.