Belonging to the Xiphiidae family, the swordfish derives its name from its long, flat bill that resembles a sword. Its scientific name, Xiphias gladius, combines the Greek word "xiphias" meaning "swordfish" and the Latin word "gladius" meaning "sword." Although the swordfish may appear similar to other billfish such as marlin, it possesses unique physiological characteristics that distinguish it as the sole member of its family.
Swordfish possess an elongated, round body and can reach impressive dimensions. They commonly grow up to 3 meters (10 feet) in length, while the largest recorded swordfish measured a remarkable 4.55 meters (14 feet 11 inches) and weighed around 650 kilograms (1,430 pounds). Females tend to be larger than males, and Pacific swordfish often achieve a greater size compared to their counterparts in the northwest Atlantic and Mediterranean. These magnificent creatures reach maturity between 4 and 5 years of age, with a maximum estimated lifespan of at least 9 years.
One of the swordfish's fascinating adaptations is its unique eye physiology. Alongside certain shark species, swordfish possess specialized organs adjacent to their eyes known as heater cells. These modified muscle cells enable the heating of the eyes and brains, resulting in an elevated temperature of 10 to 15 °C (18 to 27 °F) above the surrounding water. This extraordinary ability enhances their visual acuity, ultimately improving their hunting prowess. Among the vast array of fish species, a mere 22 possess this mechanism for heat conservation, including swordfish, marlin, tuna, and select shark species.
Movements and Feeding Habits: Swordfish are solitary creatures, preferring to swim alone or in loosely formed aggregations, maintaining a distance of up to 10 meters (35 feet) from neighboring individuals. Basking at the water's surface, they occasionally expose their first dorsal fin, captivating observers with their majestic presence. These remarkable fish are renowned for their powerful leaps and jumps, possibly serving to dislodge unwanted parasites or remoras.
When it comes to feeding, swordfish rely on their exceptional speed and agility to capture prey. Contrary to popular belief, their sword-like bill is predominantly used to slash at their targets, inflicting injuries that facilitate an easier catch. While the exact maximum speed of swordfish remains disputed, research suggests a more conservative estimate of around 36 km/h (22 mph), based on related marlin species. Swordfish are known to feed on a diverse range of pelagic fish, including mackerel, barracudinas, silver hake, rockfish, herring, and lanternfishes. They also consume demersal fish, squid, and crustaceans. When hunting, larger prey are often slashed with the sword, while smaller prey are consumed whole.
Preferred Habitats and Temperature Tolerance: Swordfish thrive in temperate and tropical regions across the Atlantic, Pacific, and Indian Oceans. They exhibit a remarkable capacity to adapt to various water temperatures. While their preference lies between 18 and 22 °C (64 and 72 °F), swordfish demonstrate the broadest temperature tolerance among billfish species, capable of withstanding temperatures ranging from 5 to 27 °C (41 to 81 °F). This adaptability facilitates their highly migratory nature, as they move towards colder regions during the summer months in search of ample food sources.
During daylight hours, swordfish can be found at depths of up to 550 meters (1,800 feet), with recorded dives reaching an exceptional 2,878 meters (9,442 feet). However, they commonly feed near the surface and in near-surface waters, especially during the night. Their nocturnal foraging behavior allows them to exploit smaller fish more effectively, often ascending to the upper layers of the water column.
Natural Predators and Parasites: Fully mature swordfish face few natural predators in the ocean. However, killer whales pose a potential threat to adult swordfish. The shortfin mako shark, known for its extraordinary speed, occasionally engages in combat with swordfish, sometimes resulting in swords breaking off within the shark's head.
The swordfish, like many marine creatures, faces a wide range of parasites. More than 50 parasite species have been documented in swordfish, including remoras, lampreys, tapeworms, roundworms, Myxozoans, and copepods. Anisakis spp. larvae, identified through genetic markers, serve as potential biological tags, supporting the existence of distinct Mediterranean swordfish populations.
Human Fisheries and Conservation Efforts: Swordfish have been a target of human fisheries for centuries. Initially, traditional methods such as harpoon fishing were employed on a smaller scale. However, with the expansion of long-line fishing techniques, the global demand for swordfish surged, leading to significant overfishing concerns.
In recent years, conservation efforts and fishing regulations have been implemented to protect swordfish populations. Bans on long-lining along many coastlines have resulted in signs of recovery for these magnificent creatures. Recreational fishing has also gained popularity, with enthusiasts practicing various techniques such as deep-drop fishing. This method involves drifting to present natural baits at depth, capitalizing on swordfish behavior during daylight and nighttime hours.