Tiny reef fish challenges tuna for speed


A tiny coral reef wrasse can swim as quickly as some of the fastest fish in the ocean – and only uses half as much energy in doing so!

By flapping their fins in a figure-eight pattern, Bluelined wrasse (also known as Red-shoulder wrasse), Stethojulis bandanensis, can travel at high speeds while using 40% less energy than tuna of the same size, Australian scientists working on the Great Barrier Reef have found.

"For a long time, people thought the best high-speed swimmers were the fishes cruising in open waters, like mackerel and tunas," says Dr Chris Fulton from the ARC Centre of Excellence for Coral Reef Studies and The Australian National University.

"The study shows that these coral reef wrasses, by virtue of their unique wing-like fins, can maintain very similar speeds at a dramatically lower energetic cost," he says.

Dr Fulton explains that fish like tunas and mackerels move their bodies and tails to propel themselves through the water. While this method enables them to swim fast, it can come at a high energetic cost.

"Another way fish swim is to use their pectoral fins, those at the front of their body, to produce thrust. Fishes that do this with rounded fins tend to paddle their fins back and forth, almost like how we row a boat: they hold their fins out and pull back in a power stroke, then collapse their fins and bring them forward for a recovery stroke. This means they are producing thrust only half the time."

Bluelined wrasses, however, flap their tapered fins in a figure eight pattern that produces thrust on every stroke, making it far more energy efficient.

"This figure-eight fin sweep allows the Bluelined wrasse to create a lift force as the water flows over their fins, in a very similar way to how birds fly through the air. This means the fish are literally flying underwater.

"They also hold their body rigid while swimming to make it as streamlined as possible. They only flap their fins, slightly adjusting the angle so as to cruise along without burning up a lot of energy."

The study shows that Bluelined wrasses stand out as the highest performing swimmers for their size with respect to optimum swimming speed and energy consumption, Dr Fulton says.

Such extreme performance appears to be linked with the fish’s habitat, he says. Unlike many tail-swimmers that dwell in the open ocean, these wrasses live on shallow coral reefs where they experience some rough treatment from waves breaking over the reef.

Having a smart swimming technique has ensured these small reef fish have an evolutionary advantage in the marine environment, Dr Fulton says.

"We know fish with these wing-like fins dominate shallow reefs around the world, where in some cases they can be about 10 times more abundant than fishes with paddle-shaped fins."

The study, Energetic extremes in aquatic locomotion by coral reef fishes by Christopher J. Fulton, Jacob L. Johansen and John F. Steffensen is published in PLoS ONE.

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