Fish often travel in schools. Their mesmerizing action can appear choreographed and rehearsed as these schools bend and break in perfect timing. But there actually is no choreographer. Each fish navigates on its own. How and why each fish does what it does is what makes their schooling so puzzling to scientists. Now scientists think they have a clue as to why schooling is so common. It saves the fish energy — lots of energy.
Hundreds to thousands of fish can school together. Sometimes they move slowly and gracefully. Other times, they will dart quickly in one direction, then another.
A new study has compared the energy a fish uses as it swims. And moving in a school reduced the energy a fish used by more than half compared to when it swam alone, it found.
“The whole idea of measuring what it costs animals to move is an important one,” says George Lauder. He’s a fish biologist at Harvard University in Cambridge, Mass., and an author of the new study. Many physiologists have been looking into this for years, he notes. “This is the first paper, I think, that’s really measured that comprehensively.”
He and Yangfan Zhang, also at Harvard, shared their new findings January 19, in eLife.
Underwater sprints
Lauder and Zhang worked with giant danio (Devario aequipinnatus), small fish that love to swim.
Sometimes the team put eight at a time into a water tank shaped a bit like a racetrack. Other times, they just put in a single fish. The danio didn’t loop around the tank like race cars. Instead, they swam in one spot, like a runner on a treadmill, as a motor pushed the tank’s water around, creating a current.
As the fish swam, a special device called a respirometer (Res-pur-AH-meh-tur) measured how much oxygen they used. Oxygen helps to fuel muscles. For example, people who sprint use a lot of oxygen. Afterward, they often need a few minutes to recover and catch their breath. Here, the researchers used oxygen…
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