The swordfish (Xiphias gladius) is a large, migratory, predatory fish recognized for its distinctive, elongated, and flattened bill. This prominent feature, resembling a sword, gives the fish its common name. The swordfish is the sole member of the family Xiphiidae.
Defining Characteristics
Its most defining characteristic is its long, flat bill, which can make up about one-third of its body length. Unlike the rounded, spear-like bills of other billfish such as marlin, the swordfish’s bill is smooth and pointed. Composed of bone, not cartilage, this bill is primarily used for stunning or injuring prey rather than impaling it.
Swordfish have a streamlined body, enabling fast swimming. Adults reach lengths of 6.5 to 9.8 feet (2-3 meters) and weigh between 120-660 pounds (55-300 kg). Larger individuals can exceed 14 feet (4.3 meters) in length and weigh over 1,400 pounds (635 kg), making them one of the largest bony fish.
Their coloration provides camouflage in the open ocean, with a dark blackish-brown or purplish-blue dorsal side that fades to a lighter, silvery underside. Adult swordfish are scaleless and toothless. They have two dorsal fins: a tall, crescent-shaped first fin and a much smaller second fin located further back. Their broad, crescent-shaped tail fin aids in powerful swimming.
Habitat and Distribution
Swordfish are found globally across tropical, subtropical, and temperate waters in the Atlantic, Pacific, and Indian Oceans. Their wide distribution spans a latitudinal range of approximately 60°N to 45°S. These fish are primarily oceanic, often found near the surface.
They dive to considerable depths, typically from the surface down to 1,800 feet (550 meters), and have been recorded even deeper, to 2,234 meters. Swordfish undertake long seasonal migrations, moving to warmer waters in winter for spawning and cooler waters in summer for feeding. These migrations can cover thousands of miles.
Swordfish have a unique adaptation: the ability to warm their eyes and brain. Specialized organs near their eyes can elevate the temperature of these areas by 10 to 15 degrees Celsius above ambient water temperatures. This internal heating system sharpens their vision and enhances cognitive function, allowing them to hunt effectively in cold, deep, and dimly lit waters. This adaptation gives them the widest temperature tolerance among billfish, enabling them to thrive in waters ranging from 41 to 81°F (5 to 27°C).
Diet and Behavior
Swordfish are apex predators, feeding on a wide variety of prey throughout the water column, from the surface to the seafloor. Their diet includes various fish like mackerel, hake, herring, barracuda, and anchovies. They also consume cephalopods such as squid and octopus, and crustaceans.
Their hunting strategy involves using their flattened bill to slash and stun prey before consuming it. Smaller prey items are swallowed whole, while larger ones are incapacitated by the bill. Swordfish are known for their speed and agility, used to capture prey. Despite their speed, they are solitary creatures, though they may gather in areas with abundant food.
Swordfish exhibit a daily vertical migration pattern, often feeding at night in shallower, near-surface waters. During the day, they move into deeper, cooler waters, where they may rest or continue hunting. This pattern allows them to access diverse food sources across different depths and temperatures.