The Atlantic blue marlin (Makaira nigricans) is a species of marlin, endemic to the Atlantic Ocean. It is a "blue-water" species of fish that spends the majority of its life far away from land in the open sea. It is highly sought as a game fish through the means of hook and line, and the IGFA (International Game Fish Association) all-tackle world record is 1,402 pounds and 2 ounces (636 kg). Atlantic blue marlin also has some commercial value worldwide because its meat has a relatively high fat content. It is currently not considered a threatened species by the World Conservation Union. The Atlantic blue marlin is a predatory species that feeds opportunistically on a wide variety of organisms near the surface. The species is distributed in the tropical and temperate waters of the Atlantic and is more populous in the western Atlantic. Some other common English names Atlantic blue marlin are billfish, cuban black marlin, marlin, ocean gar, and ocean guard.The Atlantic blue marlin is one of three species in the genus Makaira, which is derived from the greek word machaira, meaning "a short sword or bent dagger," and the latin term machaera, which means "sword." The specific name nigricans is Latin for "becoming black." The Atlantic blue marlin is part of the billfish family Istiophoridae and is in the perch-like order Perciformes. In addition, it is in the suborder Xiphioidei and is a member of the subclass Neopterygii, which means "new wings." It is also in the class of Actinopterygii, which includes ray-finned fishes and spiny rayed fishes, and the superclass Osteichthyes, which includes bony fishes.
The Atlantic blue marlin was first described in 1802 by Bernard Germain de Lacépède. Some other names that have been used in the past include the following: Histiophorus herschelii Gray 1838, Tetrapturus herschelii Gray 1838, Makaira ampla ampla Poey 1860, Tetrapturus amplus Poey 1860, Orthocraeros bermudae Mowbray 1931, and Makaira perezi Buen 1950.The Atlantic blue marlin's body is blue-black above, with a silvery white underside. It has two dorsal fins and two anal fins. Its first dorsal fin (going from front to back) has 39 to 43 rays, which are bony spines that support fins, and its second dorsal fin has 6 to 7 rays. Its first anal fin, which is similar in shape and size to the second dorsal fin, has 13 to 16 rays, and the second anal fin has 6 to 7 rays. The pectoral fins, which have 19 to 22 rays, are long and narrow and can be drawn in to the sides of the fishes body. The pelvic fins are shorter than pectorals, have a poorly developed membrane, and are depressible into ventral grooves. Its first anal fin, along with its pectoral and caudal fins, can be folded down into grooves for better streamlining. It has a long, stout bill.Both the jaws and palatines, which is the roof of the mouth, are covered with small, file-like teeth. It has about fifteen rows of pale, cobalt-colored stripes, each of which has round dots and/or thin bars, that are located on both sides of the fish. Its body is covered with thick, drawn out, bony scales that have one, two, or three posterior points with one being the most common. The lateral line system, which is a group of neuromasts rooted in lateral line canals that are used to perceive weak water motions and large changes in pressure, is reticulated and has the appearance of a net. It is obvious in immature specimens but is unclear in adults, as it becomes increasingly embedded in the skin. The first dorsal fin membrane is dark blue or almost black. It does not have any dots or marks. Other fins are normally brownish-black, sometimes with a hint of dark blue. The bases of the first and second anal fins have a hint of silvery white. The anus is placed just in front of the origin of the first anal fin. It has twenty-four vertebrae, of which eleven are precaudal and thirteen are caudal. Males rarely exceed 160 kilograms (350 lb) in weight, and females will commonly weigh over 540 kilograms (1,200 lb).
Atlantic blue marlin are capable of rapidly changing color and usually show a bright blue coloration when hunting. The coloration is a result from exposed iridophores that are mediated by adrenergic stimulation.The distribution of Atlantic blue marlin expands in a northerly direction during the warmer months and contracts towards the equator during colder months.
Evidence shows that there are two-way movements between the Caribbean Islands and Venezuela and the Bahamas, and at least one-way travel from St. Thomas to West Africa. It is unknown whether or not the trans-Atlantic fish ever return to the western Atlantic, and scientists will not know until there is an extensive tagging project in the eastern Atlantic. Several of the fish in a study were recaptured in the same general area as where they were tagged. This implies that the fish were repeat travelers returning to the area after being free for multiple years. However, there is not enough data to accurately determine seasonality of movements.The Atlantic blue marlin lives in the tropical and temperate waters of the Atlantic Ocean. Of all the billfishes, the blue marlin is the most tropical. The latitudinal range of Atlantic blue marlin changes seasonally and extends from about latitude 45°N to about latitude 35°S. It is less abundant in the eastern Atlantic where it mostly occurs off Africa between the latitudes of 25°N and 25°S. The Atlantic blue marlin usually occurs in waters warmer than 24 °C (75 °F), but has been found at surface water temperatures as high as 30.5 °C (86.9 °F) and as low as 21.7 °C (71.1 °F). Water color is also important to the Atlantic blue marlin, as it shows a preference for blue water.The Atlantic blue marlin primarily feeds on a wide range of fish (such as tuna and mackerel) and cephalopods (such as squid).It feeds mostly in near-surface waters but sometimes makes trips to deeper water for feeding. It is believed that it does not feed on the surface at night. It will swim through schools of fish at high speeds, slashing at fish with its bill, and then return to eat the dead or stunned prey. However, marlins without bills or with malformed bills have been observed as normal, healthy fish.