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Remarkable way swordfish swim revealed

Swordfish (Xiphias gladius) are large, migratory, predatory fish. The fish have a long, flat bill which gives the sword-like feature. The fish are found widely in tropical and temperate parts of the Atlantic, Pacific, and Indian Oceans. A typical swordfish is three meters (10 feet) in length; although some can reach 4.5 meters (15 feet) in length, weighing up to 650 kilograms (1,430 pounds).

Swordfish also swim very quickly. Quite how fast is uncertain, although some fishermen have reported speeds of up to 60 miles per hour (close to 100 kilometers per hour), although this has yet to be verified.

How such speeds are achieved has never been clear. It now seems that the swordfish produces oil from a gland which serves to grease its head, helping to overcome the friction from water. This, together with the streamlined body, makes it the fastest fish in the ocean.

The oil gland has been discovered from magnetic resonance imaging scans together with electron microscopy scanning. These revealed a small organ that connects to tiny pores on the head of the swordfish. The pores allow oil to ooze out and to coat the head of the fish with a thin coating of lubricant.

Later analysis showed that the oil inside the gland is identical to that found on the skin. The oil is made up of a mixture of methyl esters.

According to Science News, the tiny structures have denticles that surround the pores. These are formed from dentine and enamel, much like teeth. Here it is thought that the oil lubrication and the textured denticles combine to create a water-repelling surface. This allows the swordfish to glide through the water, experiencing only minimal drag.

On hearing the news, Popular Science (@PopSci) tweeted: “Swordfish May Grease Their Heads To Swim Faster!” Of the science paper, science writer Aatish Bhatia (@aatishb) messaged: “Love how this @edyong209 piece doesn’t just explain the cool result, but also reveals the slow process of discovery.”

The research findings are published in the Journal of Experimental Biology. The research paper is titled “Lubricating the swordfish head.”

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Written By

Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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