Tiny reef fish is surprise speedster

By Joanna Egan 28 November 2013
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A small reef fish swims faster than the quickest ocean-going species, and exerts far less energy doing so – with VIDEO.

A SMALL REEF FISH can swim faster and more efficiently than large, open-ocean species, new research has revealed.

The bluelined wrasse (Stethojulis bandanensis), found in the shallow reef waters of the Indian and Pacific oceans, reaches higher relative swimming speeds than fast, ocean-dwelling fish, while exerting 40 per cent less energy.

Tiny reef fish among ocean’s fastest

In a study published last week in the journal PLOS One, an Australian research team reveals how the wrasse, which grows to 15cm in length, can travel up to 10 times its body length per second. In contrast, tuna and billfish, which have long been considered two of the fastest fish in the ocean, advance through the water at only eight body lengths per second, while exerting far more energy than the wrasse.

“Our research debunks the idea that tail-swimming tunas and billfish represent the pinnacle of high-speed swimming in the sea,” says the study’s lead author Dr Chris Fulton, at the Australian National University in Canberra.

“We have known for a long time that fish cruising the open ocean are capable of some of the fastest known speeds for an animal swimming underwater, but we also knew that swimming at this high speed came at a very high energetic cost,” Chris says.

“Our research blows this idea out of the water by showing how these wrasses can swim in a smarter and more efficient way.”

Bluelined wrasse: energy efficient fish

Chris and his team collected wrasses from shallow reefs around Lizard Island, on the Great Barrier Reef. In tanks of fast-flowing water they studied the wrasses’ swimming technique, while measuring how quickly oxygen levels in the water depleted.

Because fish use oxygen from water to burn the energy they need to power their swimming, this process allowed the researchers to determine the wrasses’ energy consumption.

A streamlined, rigid body, wing-like fins and a flexible metabolic engine – which allows the wrasse to burn energy quickly when required – all enable the species to reach high speeds at low energetic cost.

Being able to efficiently swim at high speeds allows the wrasse to thrive in shallow reef environments, where the water movements produced by breaking waves make life difficult for poor swimmers.

How fish use fins to swim

To swim, the wrasse sweeps its fins in a figure-of-eight motion. The movement allows water flowing over the fins to create lift, in the same way that air flowing over a bird’s wing creates lift during flight. This ensures thrust is produced during every part of the stroke.

Many other fish species paddle their fins back and forth, in a similar style to the way we row a boat. This produces thrust only half the time.

“Fish can burn up to 50 per cent of their daily energy budget on swimming,” Chris says. “By using less energy on swimming these fish can use it for other things, like growing faster and bigger so they can impress potential mates, fight off rivals for territory, or escape from being eaten by a predator.”

Marine evolution and survival

Dr Nicholas Payne, at the University of New South Wales in Sydney, says the findings shed light on evolution: “This study represents a fascinating example of the adaptations marine animals develop in order to persist in highly variable environments.”

“By examining physiological adaptations in reef fishes, studies such as these improve our ability to predict the response of these animals to future environmental changes, such as those driven by climate change,” he says.

Chris says the findings could also revolutionise underwater locomotion. “Taking advantage of the efficient design that many millions of years of evolution has produced in the bluelined wrasse, we could build our next generation of underwater vehicles with the same fin shape and flapping fin motion to achieve high cruising speeds for much less power consumption.”

“This is a fascinating insight,” agrees Professor David Bellwood, from James Cook University in Queensland. “I can see applications from flying submarines and yachts, to new ways of pumping fluids.”

Credit: Cayne Layton

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