Swordfish, Xiphias gladius
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Description & Behavior
Swordfish, Xiphias gladius (Linnaeus, 1758), aka broadbills, are named for their long "bill" and, although they resemble members of the billfish Family Istiophoridae, they are actually the sole member of the Xiphiidae family. The bill of the swordfish is longer than other billfishes and unlike other billfishes, swordfishes do not have teeth in their jaws, nor do mature swordfish have scales. Juveniles hatch with scales that remain until the swordfish reaches a length of about 1 m. Juveniles also have a lateral line until they reach about the same length.
Swordfish reach a maximum length of about 4.5 m and a maximum weight of 650 kg. Females are typically larger than males. On average, swordfish caught by commercial fisheries in the Pacific, where the largest swordfish are found, measure an average of 1.2-1.9 m. Atlantic swordfish reach about 320 kg in weight and adult swordfish in the Mediterranean typically weight less than 230 kg.
Swordfish have 2 dorsal fins, one quite large followed by a smaller one. They also have 2 anal fins, again with the second much smaller than the first. Swordfish have no pelvic fins. The fins are brown to dark brown in color and the rest of the body is blackish-brown on the dorsal (upper) side fading to a lighter shade on the ventral (under) side.
World Range & Habitat
Swordfish, Xiphias gladius, are found worldwide in the Atlantic, Pacific, and Indian Oceans in tropical, temperate, and sometimes cold waters at depths between 200-600 m between 5-27°C. Swordfish found in the Mediterranean are thought to consist of a separate stock from that of the Atlantic, however they are not totally isolated.
» Video of a swordfish captured from submersible video camera at 536.45 m [NOAA Ocean Explorer: Operation Deep Scope]
Swordfish have the widest temperature range of any billfish and migrate seasonally to warmer waters in winter and cooler waters in summer. This highly migratory species can often be found where ocean currents meet and productivity is high. Although the swordfish is typically found in shallow waters, they are thought to swim as deep as 650 m. They are uniquely adapted to cold, deep waters by the presence of specialized tissue near the eyes that heats the brain through the tissue's blood supply, which is a vascular system similar to that used to heat and cool the bodies of other large pelagic fish species such as tuna. These adaptations help the fish move quickly through rapid temperature changes in the water column.
Feeding Behavior (Ecology)
Xiphias gladius are apex predators that feed throughout their depth range on other pelagic fishes, squids and other cephalopods. They use their "sword" to slash larger prey while smaller prey are consumed whole.
Predators of adult swordfish, besides humans, include marine mammals such as orcas (killer whales) and juveniles are eaten by sharks, marlins, sailfishes, yellowfin tunas, and dolphinfishes (mahi mahi).
Swordfish reach sexual maturity between 5-6 years of age and live up to 9 years. Little is known about the reproductive behavior of swordfish except that spawning tends to occur in warmer waters year round and during the spring and summer months in cooler regions. Swordfish have been observed spawning in the Atlantic ocean at 75 m deep. Another well-known spawning site is the Mediterranean where males have been observed chasing females between July-August off the coast of Italy.
Females carry between 1-29 million eggs, which are fertilized externally. The eggs measure 1.6-1.8 mm in diameter and begin developing into embryos about 2.5 days after they are fertilized.
As mentioned above, swordfish morphology changes dramatically as they mature. The pelagic larvae measure about 4 mm long when they are hatched and are born with a short snout and prickly scales. The bill begins to develop when the larvae reach 12 mm in length and the body begins to narrow. At this stage, the dorsal fin runs the length of the body until the swordfish reaches about 23 cm in length. As the swordfish grows, the dorsal fin develops into a single lobe and is followed by development of the smaller dorsal fin at 52 cm.
Conservation Status & Comments
Swordfish, Xiphias gladius, are a popular species for commercial fisheries worldwide and are primarily caught by longliners. Before this method of fishing became popular, swordfish were caught using harpoons.
The majority of the world's swordfish catch is taken from the Pacific each year, followed by takes from the Atlantic, then the Indian Ocean. The Pacific swordfish fishery is active in the northwestern Pacific, off southeastern Australia, northern New Zealand, the southeastern tropical Pacific, and Baja California, Mexico. Demand for swordfish in North America and Europe remains high, which has put tremendous pressure on swordfish stocks (wild populations); however, warnings of toxic methylmercury levels may help counter this pressure if publicly known.
In the north Atlantic, protective measures have been introduced protecting juvenile swordfish, which has helped swordfish populations replenish.
References & Further Research
Research Xiphias gladius » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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