How Fast Can a Swordfish Swim? Speed Claims Checked

Where do the swordfish speed figures come from?

The swordfish has a reputation as one of the fastest fish in the sea. Books, websites and even scientific papers describe it as reputedly the fastest swimmer on Earth, and figures of about 97–100 km/h (60 mph) are widely repeated. NOAA Fisheries gives a lower figure, saying that Atlantic swordfish can swim at up to 80 km/h (50 mph).

None of these numbers comes from a measurement of a freely swimming swordfish. Their origin is unclear, much like the famous 110 km/h (68 mph) claimed for the sailfish, which goes back to hand-timed fishing tests in which a hooked fish pulled line off a reel. A hooked fish that is leaping and thrashing does not give a reliable reading of swimming speed.

Why is a swordfish’s speed so hard to measure?

Swordfish live in the open ocean, travel alone and spend the day hundreds of meters below the surface. They are too large and too wide-ranging to keep in tanks, so the methods used to time small fish in laboratory flumes, which are channels of flowing water, cannot be used.

Electronic tags have taught scientists a great deal about where swordfish travel and how deep they dive, but sprints last only seconds and are easy to miss. Tags attached to other billfish show that these fish spend most of their time cruising slowly. Blue marlin, for example, rarely swim faster than about 2 m per second, or 7 km/h (4.5 mph). High speed is saved for brief attacks on prey and escapes from predators.

What do studies of billfish suggest?

Because swordfish have never been clocked, the best evidence comes from their relatives. In 2015, researchers filmed wild sailfish hunting sardines with high-speed cameras and fitted them with accelerometers, motion sensors that record each tail beat. The sailfish burst at about 7 m per second, or 25 km/h (16 mph), and never exceeded 10 m per second, or 36 km/h (22 mph).

A second study, published in 2016, measured how quickly the fast-twitch swimming muscle of sailfish and three other ocean predators can contract. The speed of each contraction limits how fast a fish can beat its tail, and so sets a ceiling on speed. The highest estimate was for sailfish, at about 8.3 m per second, or 30 km/h (19 mph).

A 2020 study offered another clue. By calculating take-off speeds from videos of 14 species of fish and cetaceans (whales and dolphins) leaping out of the water, the researchers found that the fastest breaches, made by animals about 2 m (6.5 ft) long, reached nearly 11 m per second, or about 40 km/h (25 mph). Such leaps may represent some of the hardest bursts of effort these animals ever make.

Is there a physical speed limit for fish?

There appears to be. When water flows very fast over a fin, the pressure on its surface can drop so low that bubbles of water vapor form and then collapse, a process called cavitation. The tiny shock waves from collapsing bubbles damage tissue, just as they pit and wear down ship propellers.

A 2008 analysis of fish and cetaceans that swim with crescent-shaped tails, the design used by billfish, tunas and dolphins, concluded that large swimmers a few meters below the surface cannot exceed about 10–15 m per second, or 36–54 km/h (22–34 mph), without cavitation. The limit rises with depth, because higher water pressure helps prevent bubbles from forming, but deep water is also cold, and cold muscle contracts more slowly. A swordfish sprinting at 100 km/h near the surface would almost certainly damage its own fins.

How is a swordfish built for speed?

Even without a confirmed record, the swordfish is clearly a fast and powerful swimmer. Its long, rounded body tapers at both ends, and adults have smooth skin with no scales. Most of the thrust comes from a stiff, crescent-shaped tail on a narrow tail base with a keel on each side, the same high-speed design seen in tunas and mako sharks.

Swordfish also keep their red swimming muscles warmer than the surrounding water, using a heat-exchange system in the blood vessels. Laboratory tests in 2020 showed that swordfish red muscle produces more power at fast tail-beat rates when it is warm. A separate heater organ warms the eyes and brain, as explained in How do swordfish heat their eyes?

The most surprising discovery came in 2016, when scientists scanning swordfish heads found an oil-producing gland near the base of the sword. Tiny vessels carry the oil to pores in the skin of the head, each surrounded by small tooth-like scales called denticles. The researchers suggested that this oily, water-repellent layer may reduce friction drag over the front of the head. The idea is promising but untested in living fish, and whether the sword itself helps the swordfish cut through the water is still unknown. What the sword does do is covered in What is a swordfish’s sword for?

Is the swordfish the fastest fish?

It may be one of the fastest, but there is no reliable way to crown a winner. Swordfish, sailfish, marlins, tunas, wahoo and the shortfin mako shark are all fast predators, and none has an accepted, measured top speed. The modern evidence suggests that the fastest of them reach a few tens of kilometers per hour in short bursts, far below the record-book figures, and rely as much on sudden acceleration, sharp turns and well-aimed strikes of the bill as on raw speed. Other contenders on land, in the air and in the sea are compared in fastest animals.