The swordfish, Xiphias gladius, is a large, specialized marine predator. As the sole member of the family Xiphiidae, it is unique among billfish. This highly migratory fish is found in tropical, subtropical, and temperate waters across the Atlantic, Pacific, and Indian Oceans. Its common name is derived from the most prominent feature of its anatomy.
The Distinctive Sword
The defining characteristic of the swordfish is the elongated, flattened bill that extends from its upper jaw, which is correctly termed a rostrum. This protrusion is a hard, bony structure that is an extension of the fish’s cranium, giving it remarkable rigidity and strength. The bill can account for approximately one-third of the fish’s total body length, making it proportionally longer than the bills of other billfish like marlin.
Unlike the rounded bill of a marlin, the swordfish rostrum has a noticeably flattened-oval cross-section, which contributes to its broad, blade-like shape. This morphology is critical to the way the swordfish hunts in the open ocean.
The rostrum is not used for spearing prey, as is often mistakenly believed, but rather as a weapon to stun and incapacitate. The swordfish uses powerful, swift, lateral slashing movements to strike at schools of fish and squid. This method of stunning prey is highly effective for a predator built for speed and efficiency.
Adult Body Shape and Coloration
Beyond its famous bill, the adult swordfish exhibits a fusiform, or torpedo-shaped, body that is stout and rounded, a shape optimized for moving quickly through water. Their streamlined design allows them to reach speeds estimated to be around 50 miles per hour. This adaptation is supported by a large, crescent-shaped caudal (tail) fin, which provides immense propulsion.
The adult swordfish skin is notable for being smooth, as mature individuals lose the scales and teeth they possessed in their juvenile stage. This lack of scales reduces drag, further enhancing the fish’s speed and hydrodynamic efficiency.
The coloration of the swordfish provides effective camouflage through a pattern known as countershading. The upper (dorsal) surface is a dark, blackish-brown or metallic blue, helping the fish blend with the dark depths when viewed from above. This dark coloring transitions sharply to a lighter, silvery-white or light brown on the lower (ventral) side.
This lighter underside makes the fish difficult to spot from below against the brighter surface waters. The fin structure also contributes to the adult’s appearance. It features a tall, rigid, and curved first dorsal fin that is completely separate from the much smaller, rearward second dorsal fin. Adult swordfish also lack pelvic fins entirely, a feature that distinguishes them from other billfish.
Size and Growth Stages
Swordfish are one of the largest predatory fish, commonly reaching lengths of about 3 meters (10 feet) and weights of up to 650 kilograms (1,430 pounds) for the largest individuals. Females typically grow larger and live longer than males, with most fish exceeding a certain weight threshold being female.
The appearance of the swordfish changes significantly throughout its life, a process called ontogenetic shift. Larvae, which hatch at only about four millimeters long, are born with a short snout and a covering of prickly scales. As they grow, the bill begins to develop, and the small teeth they possess are gradually lost.
Juveniles initially have a single, continuous dorsal fin that runs the length of their body, unlike the two separate fins of the adult. These juvenile scales and the lateral line disappear once the fish reaches a length of approximately one meter.