Self-Lubricating Swordfish Secrete Oil to Swim Faster

Greased lightning, go greased lightning

Biodiversity Heritage Library, via Flickr

Swordfish may look like formidable beasts, what with their namesake prong jutting out from their noses. That pointy-looking nose, however, isn't as strong as it may look, thanks to a thin section of bone at its base that shares the space with a particularly large gland. Now, after years of puzzling over its purpose, scientists believe they finally have the answer: the gland helps swordfish swim faster by coating their heads in oil.

In a recent study published this week in the Journal of Experimental Biology, scientists from University of Groningen in the Netherlands say that the mysterious gland is linked to pores on the fish’s head through a system of capillaries. These pores then secrete an oily film that could potentially reduce the drag that swordfish experience when swimming—with top speeds reaching over 62 miles per hour, Mary Beth Griggs reports for Popular Science.

Over the last 20 years, study authors John Videler and Roelant Snoek meticulously studied the swordfish, using magnetic resonance imaging scans (MRIs) to figure out how the nosy fish could swim so fast. They discovered the gland at the time, but weren’t sure of it’s purpose, Ashley Taylor reports for The Scientist. Then, last year another group identified the weak spot at the base of the swordfish’s sword, and Videler and Snoek took another look at the gland. At first, they didn’t find anything new—but then, Snoek accidentally dropped a light right on the fish’s head.

“All of a sudden [Snoek] saw this network of vessels that were connected to the oil gland,” Videler says in a statement. “And then we found that by heating up the gland you could see oil come out of these tiny little holes.”

According to Snoek and Videler it’s possible that this oil, combined with the swordfish’s sandpaper-like skin, helps to reduce drag on the fish by allowing the oil to coat as much surface area on its head as possible. By repelling water molecules from its head as it swims, the oil could be one reason swordfish are so speedy, Sarah Laskow writes for Atlas Obscura.

“I find this quite fascinating,” ecologist Jens Krause of Berlin’s Humboldt University, who was not involved in the study, tells Taylor. “Much is really left as speculation. Nevertheless, I think it’s an interesting idea that deserves publication and will undoubtedly require testing.”

While the next step in investigating this theory would generally be to test it on a living fish, in this case that’s easier said than done. Because swordfish are large and fast swimmers, it is very hard to keep them in captivity, Griggs reports. To get around this, Videler and his colleagues may have to resort to using models to try and determine whether this oil does in fact reduce drag as the fish zooms through the sea. In the meantime, other researchers are curious to see whether this gland is unique to swordfish, or if there are other similar fish that use the same technique to speed up their swimming.

“I’ve got lots of billfish heads in my freezer,” Krause tells Taylor. Perhaps they too grease up for speed.

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