Snoek's so-called "light-bulb moment" involved an actual light bulb - he accidentally dropped a light onto the fish that he and Videler were dissecting, illuminating those capillaries that were connected to the gland, Videler explained in a statement.
The researchers injected the capillaries with ink to confirm their connection to pores on the skin's surface, and found that clusters of pores of varying sizes covered a significant portion of the head. During another test, they warmed the gland with a hair dryer to stimulate oil flow though the pores - and it began to flow "as soon as the oil gland was heated." In a living swordfish, the oil gland would be heated by muscles near the eyes, according to the scientists.
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Oil-slick skin would be more water-resistant. In combination with the bill's texture, a greasy head could reduce drag in the water by about 20 percent, the authors estimated in the study. They suggested that future investigations could test the hypothesis by creating mathematical models of the swimming performance of swordfish, which is virtually impossible to monitor in the wild.
But perhaps the most important lesson to be learned is that there are still many mysteries about animal biology that remain to be solved - even in familiar animals, Videler told Live Science.
"Entirely new organs can still be discovered in big, popular animals using modern techniques," he said. "Even swordfish will have more to offer - we only need to study its anatomy better."
And though Videler - now age 75 - is retired, he has no plans to stop investigating the natural world anytime soon.
"There is so much to learn from nature," he added. "I hope to remain curious until I die."
The findings were published online today (July 6) in the Journal of Experimental Biology.
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Original article on Live Science.