The swordfish (Xiphias gladius), also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, sword-like, pointed bill. They are the sole member of the family Xiphiidae. They are a popular sport fish of the billfish category. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood. These fish are found widely in tropical and temperate parts of the Atlantic, Pacific, and Indian Oceans, and can typically be found from near the surface to a depth of 550 m (1,800 ft), and exceptionally up to depths of 2,878 m (9,442 ft). 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.
Taxonomy and etymology The swordfish is named after its long, pointed, flat bill, which resembles a sword. The species name, Xiphias gladius, derives from Greek ξιφίας (xiphias, "swordfish"), itself from ξίφος (xiphos, "sword") and from Latin gladius ("sword"). 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. The swordfish appears to have a deep evolutionary divergence from all other billfish, dating to at least the middle Paleocene. In the past, several fossil billfish genera, such as the giant Xiphiorhynchus, were attributed to the family Xiphiidae. However, Rust et al (2025) found many of these genera to form their own clade, Xiphiorhynchidae, that likely forms the sister group to the marlins and sailfish in the family Istiophoridae. In contrast, the small-sized Blochiidae from the Early Eocene were found to be the sister group to the swordfish. The earliest known fossil remains of true swordfish date to the Middle Miocene, where the articulated partial posterior skeleton of a juvenile Xiphias has been recorded from Paratethyan deposits in Poland. However, even this record is uncertain. Outside of this one record, all other fossil records of swordfish are known only from the Pliocene of Italy (where a nearly complete fossil skeleton is known) and North Carolina, US.
Description They commonly reach 3 m (10 ft) in length, and the maximum reported is 4.55 m (14 ft 11 in) in length and 682 kg (1,500 lb) in weight. 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. Females are larger than males, and Pacific swordfish reach a greater size than northwest Atlantic and Mediterranean swordfish. They reach maturity at 4–5 years of age, and the maximum age is believed to be at least 9 years. 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.
Temperature regulation Swordfish are ectothermic animals. Along with some species of sharks, they have special organs next to their eyes called heater cells which function to heat their eyes and brains. Their eyes are heated to temperatures measured between 10 and 15 °C above the surrounding water temperature; this heating greatly improves their vision and, consequently, their predatory efficacy. The swordfish is one of 22 species of fish – including the marlin, tuna, and some sharks – known to have a heat-conservation mechanism.
Behavior and ecology
Movements and feeding The popular image of the swordfish skewering its prey with its nose is based on little evidence. In a typical environment, swordfish most likely use their noses to slash at prey and inflict weakening injuries. The hypothesis that they may use their noses as spears in a defensive capacity against sharks and other predators is still under review. Mainly, the swordfish relies on its great speed and agility in the water to catch its prey. It is no doubt among the fastest fish, but the basis for the frequently-quoted speed of 100 km/h (60 mph) is unreliable. Research on related marlin (Istiophorus platypterus) suggest a maximum value of 36 km/h (22 mph) is more likely. Swordfish are not schooling fish. They swim alone or in very loose aggregations, separated by as much as 10 m (35 ft) from a neighboring swordfish. They are frequently found basking at the surface, airing their first dorsal fin. Boaters report this to be a beautiful sight, as well as the powerful jumping for which the species is known. This jumping, also called breaching, may be an effort to dislodge pests, such as remoras or lampreys.
Swordfish prefer water temperatures between 18 and 22 °C (64 and 72 °F), but have the widest tolerance among billfish, and can be found from 5 to 27 °C (41 to 81 °F). This highly migratory species typically moves towards colder regions to feed during the summer. Swordfish feed daily, most often at night, when they rise to surface and near-surface waters in search of smaller fish. During the day, they commonly occur to depths of 550 m (1,800 ft; 300 fathoms) and have exceptionally been recorded as deep as 2,878 m (9,442 ft; 1,574 fathoms). Adults feed on a wide range of pelagic fish, such as mackerel, barracudinas, silver hake, rockfish, herring, and lanternfishes. They also take demersal fish, squid, and crustaceans. In the northwestern Atlantic, a survey based on the stomach content of 168 individuals found 82% had eaten squid and 53% had eaten fish, including gadids, scombrids, butterfish, bluefish, and sand lance. Large prey are typically slashed with the sword, while small ones are swallowed whole.
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