Featured Image: Brian J. Skerry, National Geographic Creative
By: Eva Gruber
Swordfish are known to be some of the fastest swimmers in the marine world.
For a long time, scientists studying the majestic fish were aware of a gland that sits at the base of the swordfish’s bill. To make room for it, the bone of the skull is thinner than surrounding areas. This makes its an area where the bill can break rather easily.
In fact, broken swordfish bills have been found stuck in the hulls of boats that the fish apparently attacked. But other than being a weak spot where the bill could break off, its purpose was completely unknown.
Now, this gland has been discovered to provide these high-octane predators a special advantage in gaining top speeds in pursuit of prey. The gland provides aa lubricating oil that lends the swordfish enough of an advantage in hunting that it has persisted through the millennia.
The swordfish is known to be one of the fastest fishes in the sea. Clocked at speeds of 62 mph, they might very well be the fastest swimmers on the planet. Powered by up to 1,000 pounds of dense muscle, their streamlined bodies cut through the water like a finely-tuned hydrodynamic machine as they hunt their prey.
Photo Credit:Pete Oxford via fineartamerica
Its bill, which can reach up to 45% of its body length, is used to slash through schools of fish, stunning individuals who are then swallowed whole.
MRI scans taken by the study’s lead author, John Videler, a biologist and professor at Groningen University, revealed the structure of the gland and its surrounding tissue.
At first, Videler and his colleagues believed the gland played a part in the fishes olfactory system, as it was located directly below nasal sacs. But they couldn’t establish a direct link between the gland and the olfactory system.
Then, study co-author Roelant Snoek discovered a network of capillaries that carried the oil the gland produced to the surface of the skin of the head.
Further experiments on dissected swordfish proved that the gland’s oil seeped out of pores on the fishes head, and that the oil flowed easily when surrounding tissue was heated. In a live fish, the gland would be heated by the muscles of the eye as the swordfish swam.
Photo Credit: John J. Videler via livescience.com
The purpose of the oil is rather clear – skin slicked with oil is more water-resistant and therefore more hydrodynamic as it reduces drag as the fish propels itself forward. The authors of the study estimated that this oil could reduce drag by as much as 20%. That’s a very significant amount! Looks like this lubricating ability is worth having.
Studies like these prove that even with some of our planet’s most familiar species, great discoveries still await those curious enough to investigate.
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