Billfish

The term billfish refers to a group of predatory fish characterised by prominent bills, or rostra, and by their large size; some are longer than 4 m (13 ft). Billfish include sailfish and marlin, which make up the family Istiophoridae, and swordfish, sole member of the family Xiphiidae. They are apex predators which feed on a wide variety of smaller fish, crustaceans, and cephalopods. These two families are sometimes classified as belonging to the order Istiophoriformes, a group with origins in the Late Cretaceous around 71 million years ago with the two families diverging from one and another in the Late Miocene around 15 million years ago. However, they are also classified as being closely related to the mackerels and tuna within the suborder Scombroidei of the order Perciformes. However, the 5th edition of the Fishes of the World does recognise the Istiophoriformes as a valid order, albeit including the Sphyraenidae, the barracudas. Billfish are pelagic and highly migratory. They are found in all oceans, although they usually inhabit tropical and subtropical waters; swordfish are found in temperate waters, as well. Billfish use their long spears or sword-like upper beaks to slash at and stun prey during feeding. Their bills can also be used to spear prey, and have been known to spear boats (probably accidentally), but they are not normally used in that way. They are highly valued as gamefish by sports fishermen. The term billfish refers to the fishes of the families Xiphiidae and Istiophoridae. These large fishes are 'characterized by the prolongation of the upper jaw, much beyond the lower jaw into a long rostrum which is flat and sword-like (swordfish) or rounded and spear-like (sailfishes, spearfishes, and marlins).' The 12 species of true billfish are divided into two families and five genera. One family, Xiphiidae, contains only one species, the swordfish Xiphias gladius, and the other family, Istiophoridae, contains 11 species in four genera, including marlin, spearfish, and sailfish. Controversy exists about whether the Indo-Pacific blue marlin, Makaira mazara, is the same species as the Atlantic blue marlin, M. nigricans. FishBase follows Nakamura (1985) in recognizing M. mazara as a distinct species, 'chiefly because of differences in the pattern of the lateral line system'. A number of other fishes have pronounced bills or beaks, and are sometimes referred to as billfish, despite not being true billfish. Halfbeaks look somewhat like miniature billfish, and the sawfish and sawshark, which are cartilaginous fishes with long, serrated rostrums. Needlefish are sometimes confused with billfish, but they are 'easily distinguished from the true billfish by having both jaws prolonged, the dorsal and anal fins both single and similar in size and shape, and the pelvic fins inserted far behind the pectorals.' Paddlefish have elongated rostrums containing electroreceptors that can detect weak electrical fields. Paddlefish are filter feeders and may use their rostrum to detect zooplankton. Billfish have a long, bony, spear-shaped bill, sometimes called a snout, beak or rostrum. The swordfish has the longest bill, about one-third its body length. Like a true sword, it is smooth, flat, pointed and sharp. The bills of other billfish are shorter and rounder, more like spears. Billfish normally use their bills to slash at schooling fish. They swim through the fish school at high speed, slashing left and right, and then circle back to eat the fish they stunned. Adult swordfish have no teeth, and other billfish have only small file-like teeth. They swallow their catch whole, head-first. Billfish don't normally spear with their bills, though occasionally a marlin will flip a fish into the air and bayonet it. Given the speed and power of these fish, when they do spear things the results can be dramatic. Predators of billfish, such as great white and mako sharks, have been found with billfish spears embedded in them. Pelagic fish generally are fascinated by floating objects, and congregate about them. Billfish can accidentally impale boats and other floating objects when they pursue the small fish that aggregate around them. Care is needed when attempting to land a hooked billfish. Many fisherman have been injured, some seriously, by a billfish thrashing its bill about. Billfish are large swift predators which spend most of their time in the epipelagic zone of the open ocean. They feed voraciously on smaller pelagic fish, crustaceans and small squid. Some billfish species also hunt demersal fish on the seafloor, while others descend periodically to mesopelagic depths. They may come closer to the coast when they spawn in the summer. Their eggs and larvae are pelagic, that is they float freely in the water column. Many grow over three metres (10 feet) long, and the blue marlin can grow to five metres (16 feet). Females are usually larger than males.