Wednesday, 20 July 2016

Secret to Swordfish's Speedy Swimming Found

By Mindy Weisberger, Senior Writer | July 7, 2016 07:02am ET

A swordfish's impressive saber-like bill might inspire visions of swashbuckling fencers wielding flashing blades. But in reality, this protruding proboscis is more vulnerable than you might expect.

There is a weak spot at the base of the bill where it joins the skull. The bone thins at this spot to make room for an oversized gland. Scientists have just discovered what this mysterious gland might be used for — faster swimming.

Researchers have found that the gland produces oil that covers the swordfish's head with a slippery coating. By generating this greasy film, the gland could reduce drag and help the fish cut through the water more efficiently, contributing to its swim speed.

Built for speed
Swordfish have powerful yet streamlined bodies that are literally built for speed. They are thought to be the fastest swimmers on Earth and have been clocked at an estimated 62 mph (100 km/h), according to the study authors.

A swordfish uses its signature bill — which can reach up to 40 to 45 percent of its body length — in sweeping motions to slash and stun its prey. But it also plays a part in swimming. The bill's surface is porous and rough, the authors noted — a feature that previous studies had linked to drag reduction.

However, recent studies had also revealed a noticeable weakness at the bill's base that puzzled the scientists, prompting them to take a closer look. 

Luckily, the study's lead author, John Videler, a biologist and professor at Groningen University in the Netherlands, had scanned a pair of adult swordfish in 1996 and 1997 using magnetic resonance imaging (MRI). He captured 657 images showing the insides of the fish, from the tips of their bills to the ends of their tails.

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