Swordfish

The swordfish is a large, solitary pelagic predator and the sole member of the family Xiphiidae, distinguished by its long, flat, sword-like upper jaw extension. Found in tropical and temperate oceans worldwide, it is among the fastest and most powerful open-ocean fish, capable of diving to great depths in pursuit of prey thanks to specialized heat-retaining tissue around its eyes and brain that improves vision in cold, dark water. Unlike marlin and sailfish, adult swordfish lack pelvic fins and scales, and their bill is flattened rather than round in cross-section. The species is a highly prized sport fish and supports significant commercial fisheries worldwide.

• Long, cylindrical, streamlined body
• Extremely long, flat, sword-shaped bill (longer and flatter than the rounded bills of marlin)
• Dark bronze to purplish-brown back, fading to lighter, sometimes silvery, sides
• Tall, rigid, crescent-shaped dorsal fin (non-collapsible, unlike sailfish)
• Deeply forked, stiff tail fin
• No pelvic fins in adults, unlike marlin and sailfish
• Adults typically 2-4.5 m

The flattened, sword-like bill cross-section and absence of pelvic fins reliably separate swordfish from the rounder-billed marlin and sailfish. Adults also lack scales entirely, giving the skin a smooth, leathery texture distinct from the coarser, scaled skin retained by other large billfish.

Swordfish range throughout tropical, subtropical, and temperate oceans worldwide, tolerating a very broad temperature range from about 5-27 degrees C due to specialized cranial heater tissue that warms their eyes and brain. They undertake extensive vertical migrations, feeding near the surface at night and diving to depths of 500 m or more, sometimes beyond 800 m, during the day to follow prey such as squid in deep scattering layers. Adults are typically solitary and occupy open ocean far from shore, though they may approach continental shelf edges and seamounts where prey concentrates.

Swordfish are solitary, highly migratory predators that use their bill to slash and stun prey such as squid and schooling fish before consuming them. Their daily vertical migration between warm surface waters at night and cold deep water by day is supported by a unique brain- and eye-warming organ that improves visual acuity in the cold, dim depths. Spawning occurs in warm surface waters, where females release large numbers of small pelagic eggs fertilized externally, with no parental care afterward. As apex predators of the open ocean, swordfish help regulate populations of squid and mid-water fish, and they are also a globally significant recreational and commercial sport fish.