The swordfish is hailed as one of the fastest swimming fish in the sea. Though it has not been accurately measured as to how fast it can swim underwater, a study done in 2009 said it can achieve unimaginably high momentum at an approximate maximum speed of 130 kilometers per hour.
But have you ever wondered what makes swordfish the speed champion in the sea? Scientists tried to unravel the century-long mystery in a two-decade study.
A recent study published in the Journal of Experimental Biology said the answer is not on its famous bill that can slice its way through water, but actually in its complex organ consisting of an oil-producing gland.
John Videler, a biologist at the Netherlands' Groningen University, along with biologist Roelant Snoek, came across a swordfish in 1995. Using magnetic resonance imaging, the scan revealed an oil gland.
At that time, it was unclear yet how the oil gland functions and its purpose. But Videler told The Scientist that he was puzzled when he discovered a weak spot at the swordfish's bill.
Recalling the incident that sparked his curiosiy, he told the site that he was surprised when the bill broke off when he accidentally banged it on the door.
Twenty years later, they decided to look at it once more, and again, by accident, they found the most feasible answer to the swordfish's biggest mystery.
As per EurekAlert, when Snoeka accidentally dropped a light bulb onto the fish's skin, the function of the gland was revealed.
"All of a sudden he saw this network of vessels that were connected to the oil gland," says Videler. "And then we found that by heating up the gland you could see oil come out of these tiny little holes."
Using electron microscopy, tiny holes connected to the gland by the capillaries were revealed. So as water brushes rushes by the head of the swordfish, the glands secrete oil.
The researchers think that the oil lubricates the swordfish's body, making it faster by an additional 20 percent and helping them hunt agile squid and fish.
"We hypothesize that the oil layer, in combination with the denticles, creates a super-hydrophobic layer that reduces streamwise friction drag and increases swimming efficiency," the study read.
To fully prove the analysis of the researchers, further studies are needed. However, because the swordfish cannot be kept in captivity, the research faces challenges.
Nicole Sharp, an aerospace engineer who was not involved in the study, told National Geographic that she supports the claim of the biologists about how the oil gland acts as lubrication. However, she doubts the "super-hydrophobic" term, as she thinks there is insufficient denticles to produce the kind of turbulence that is need for a superhydrophobic surface.
"I'm willing to accept the hypothesis that this oil gland and capillary system provides lubrication for the swordfish that may help reduce its drag," she says. "But I'm not convinced that the fish's head qualifies as superhydrophobic."
The International Union for Conservation of Nature lists the swordfish (Xiphias gladius) as pandemic. It is found in the Atlantic, Indian, and Pacific oceans, including the Mediterranean Sea, the Sea of Marmara, the Black Sea, and the Sea of Azov.
Its depth distribution ranges normally from the surface to a depth of about 550 meters, but there are depth records down 2,878 m. It can grow up to 14 feet in length and weighs 1,200 pounds.
A full migrant species, they have no scales and teeth. The swordfish uses its sword-like bill to prey on fish as well as crustaceans and squids. Their lifespan reaches up to nine years and are currently listed as least concern, which is the lowest level in terms of conservation status.
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