They are the sole member of their family, Xiphiidae.^[6]

Taxonomy and etymology[edit]

The swordfish is named after its long pointed, flat bill, which resembles a sword. The species name, Xiphias gladius, derives from Greek ??f?a? (xiphias, "swordfish"), itself from ??f?? (xiphos, "sword") and from Latin gladius ("sword").^[5] This makes it superficially similar to other billfish such as marlin, but upon examination, their physiology is quite different and they are members of different families.^[7]

Several extinct genera are known, such as a large sized Xiphiorhynchus and Aglyptorhynchus.^[8] Unlike modern taxa these have equally long lower jaws.^{[citation needed]}

Description[edit]

They commonly reach 3 m (10 ft) in length, and the maximum reported is 4.55 m (14 ft 11 in) in length and 650 kg (1,430 lb) in weight.^[3][5] The International Game Fish Association's all-tackle angling record for a swordfish was a 536 kg (1,182 lb) specimen taken off Chile in 1953.^[2] Females are larger than males, and Pacific swordfish reach a greater size than northwest Atlantic and Mediterranean swordfish.^[5] They reach maturity at 4–5 years of age and the maximum age is believed to be at least 9 years.^[5] The oldest swordfish found in a recent study were a 16-year-old female and 12-year-old male. Swordfish ages are derived, with difficulty, from annual rings on fin rays rather than otoliths, since their otoliths are small in size.^[9]

Swordfish are ectothermic animals; however, along with some species of sharks, they have special organs next to their eyes to heat their eyes and brains. Temperatures of 10 to 15 °C (18 to 27 °F) above the surrounding water temperature have been measured. The heating of the eyes greatly improves their vision, and consequently improves their ability to catch prey.^[10][11] Of over 25,000 fish species, only 22 are known to have a mechanism to conserve heat. These include the swordfish, marlin, tuna, and some sharks.^[10][11]

Fisheries[edit]

Swordfish were harvested by a variety of methods at small scale (notably harpoon fishing) until the global expansion of long-line fishing. They have been fished widely since ancient times in places such as the Strait of Messina, where they are still fished with traditional wooden boats called feluccas and are part of the cuisine in that area.^[22][23][24]

Swordfish are vigorous, powerful fighters. Although no unprovoked attacks on humans have been reported, swordfish can be very dangerous when harpooned. They have run their swords through the planking of small boats when hurt. In 2015, a Hawaiian fisherman was killed by a swordfish after attempting to spear the animal.^[25]

Recreational fishing[edit]

Recreational fishing has developed a subspecialty called swordfishing. Because of a ban on long-lining along many parts of seashore, swordfish populations are showing signs of recovery from the overfishing caused by long-lining along the coast.

Various ways are used to fish for swordfish, but the most common method is deep-drop fishing, since swordfish spend most daylight hours very deep, in the deep scattering layer. The boat is allowed to drift to present a more natural bait. Swordfishing requires strong fishing rods and reels, as swordfish can become quite large, and it is not uncommon to use 2.5 kg (5 lb) or more of weight to get the baits deep enough during the day, up to 460 m (1,500 ft) is common.^[26] Night fishing baits are usually fished much shallower, often less than 90 m (300 ft; 50 fathoms). Standard baits are whole mackerel, herring, mullet, bonito, or squid; one can also use live bait. Imitation squids and other imitation fish lures can also be used, and specialized lures made specifically for swordfishing often have battery-powered or glow lights. Even baits are typically presented using glow sticks or specialized deepwater-proof battery operated lights.