Swordfish, Xiphias gladius Linnaeus 1758
An illustration of a Swordfish, Xiphias gladius, from Cuvier & Valenciennes, 1828, Histoire naturelle des poissons.. Source: Biodiversity Heritage Library. License: Public Domain
A large, powerful oceanic predator with a long cyclindrical, tapering body, and an extremely long, flattened, sword-like bill, used to slash prey. Swordfish are blackish-brown above, fading to a lighter brown on the underside. As adults, they lack pelvic fins, scales and teeth, and have a high dorsal fin and a relatively large anal fin.
Like some shark and tuna species, Swordfish are endothermic, with the ability to maintain body temperatures above that of the surrounding water. A highly specialized heating system located in an extraocular muscle specifically warms the eyes and brain up to 10°C–15°C above ambient water temperatures.
This important adaptation allows these highly visual oceanic predators to hunt their agile, cold-blooded prey in deep, cold waters (Fritsches et al. 2005).
Swordfish are highly valued as a commercial species and recreational species.
Swordfish, Xiphias gladius Linnaeus 1758
More Info
Distribution |
A cosmopolitan species, distributed throughout tropical and sub-tropical waters, migrating to temperate waters during summer. Swordfish are widespread in Australian waters, usually beyond the continental shelf, in depths of 0-800 m. The species generally occurs above the thermocline, preferring water temperatures of 18-22 deg C. |
Features |
Dorsal fin (1) 0, 34-49; Dorsal fin (2) 4-6; Anal fin (1) 0, 13-14; Anal fin (2) 3-4; Pectoral fin 16-18. Pelvic fins absent. Pectoral fins falcate, positioned low on body. Bill is long and flat in cross section. The lateral line is absent in adults, but visible in smaller specimens up to 1 m long. Teeth and scales absent in adults. Body is roughly cylindrical and elongate. First and second dorsal fins are well separated, but continuous in juveniles, first dorsal shrinking to adult proportions as the fish grows. Juveniles initially develop elongated upper and lower jaws, but lower jaw gradually reduces to adult shape. Juveniles also posses scales and have teeth in both upper and lower jaws. |
Size |
To a length of 450 cm (although usually smaller) and a weight of 600 kg. Females are generally larger than males, with most fish over 140 kg in weight being female. |
Colour |
Blackish-brown fading to light-brown below; first dorsal fin with blackish-brown membrane, other fins brown or blackish-brown. |
Feeding |
Slashes prey with its bill to stun or kill it before swallowing whole. Typical food items include pelagic fishes such as tuna, flying fish and barracudas, demersal prey includes hakes, gempylids and myctophids. Squid and cuttlefish species also form part of its prey. Large adults are known to hunt demersal species in temperatures as low as 5-10 degrees. |
Biology |
Australian east coast females mature at around 150 cm fork-length; males are mature at smaller sizes (around 1 m fork-length). Spawning occurs from September to March, but predominantly during the December to February period, apparently triggered by water temperatures above 24 degrees. Swordfish spawn near the surface and females produce pelagic eggs and the larvae are pelagic. Fecundity is related linearly to size. Each female spawns on multiple occasions (batch spawning), however the frequency of spawning and the number of times an individual female spawns has not been determined. During the spawning period to the sex ratio is skewed towards females, particularly in nearshore spawning areas. Worldwide the spawning season varies and may include the full year near the equator. |
Fisheries |
In Australian waters the species is fished both by Australian long-liners and Japanese ships. Catches in the eastern Australian portion of the fishery were around 2500 tonnes in 2001, and have fallen to 1600 tonnes in 2003. The species is also fished as part of the Western Australian Tuna and Billfish fishery. Catches peaked at 2100 tonnes in 2001 but have since fallen to 1100 tonnes (2003). Swordfish are targeted via the use of deep longlines or taken as bycatch on tuna longlines fished at night. Concerns have been raised that a large portion of the fish captured are immature, and that the fishery may be unsustainable. Considered a good food fish, marketed as fillets. Recreational catches appear to be restricted to incidental catches while trolling surface lures for other billfish. The Australian linefishing record is 9.5 kg. |
Conservation |
IUCN Red List: Least Concern Swordfish are highly migratory, and the species is listed in Annex I of the 1982 Convention on the Law of the Sea (FAO Fisheries Department 1994). |
Remarks |
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Similar Species |
Unlike the closely related marlins (Istiophoridae), adult Swordfish lack pelvic fins. |
Etymology |
From the Greek Xiphias meaning sword, and the Latin gladius meaning a flat sword, in reference to the flattened sword-like bill. |
Species Citation |
Xiphias gladius Linnaeus 1758, Systema Naturae Ed. X. 1: 248. Type locality: European ocean. |
Author |
Dianne J. Bray & Sascha Schultz |
Resources |
Swordfish, Xiphias gladius Linnaeus 1758
References
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