Einstein Science Reporting for Kids
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28-Nov-2003

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Fish go with the flow



Trout swimming through turbulent flow in a tank. [Image courtesy of James C. Liao]

Full size image available here

Fish seem to have a special energy-saving method for maneuvering through turbulent waters, according to a new study. These findings may help researchers design improved underwater vehicles that don't need humans to drive them or to make better "fish ladders" alongside dams. These passageways (which don't really look like ladders) allow fish to swim past the dams and continue their river journeys.



Top view of rainbow trout swimming over a gravel bed in turbulent flow. [Image courtesy of James C. Liao]

Full size image available here

The environment beneath a river's surface can be extremely chaotic. When the water flows past sticks, rocks or other objects, a string of small whirlpools, called "vortices," develops.

James Liao of Harvard University and his colleagues mimicked this environment in a large fish tank. They made the water flow past a stick and set up a high-speed camera to see how fish would react to the vortices that developed in the tank.



Surfing underwater: rainbow trout ride eddies in turbulent flow. [Image courtesy of James C. Liao]

Full size image available here

As they report in the 28 November issue of the journal Science, Liao and his team found that fish zig-zagged in between the vortices.

This motion allowed them to use the energy of each vortex to help propel them forward. In fact, the fish seem to use their bodies in the same way that a boater uses a sail to tack back and forth in the wind, according to Liao.

By attaching electrodes to their swimming subjects, the researchers also figured out that the fish were using relatively few muscles to swim in this manner.

So, even though the water around them is swirling in different directions, the fish just take it easy and go with the flow.

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