Using biomimetic robots similar to fish, the researchers found that fish that move in
“Shoals of fish are very dynamic socialsystems, ”explains senior study author Ian Cousin. “Our results explain how fish can profit from vortices created by their nearest neighbors without having to maintain fixed distances from each other.”
To answer the question whether fish can saveenergy, swimming with other fish, it is necessary to measure its energy expenditure. Accurately doing this with free-swimming fish is not possible, and past research has tried to answer this question using theoretical models and predictions.
New research, however, has overcome thisbarrier to experimental testing. Researchers have developed a three-dimensional robotic fish with a soft tail fin that swims exactly like a real fish. But unlike their living cousins, robots allow you to directly measure the energy consumption associated with swimming together, rather than alone.
In over 10,000 tests, they tested the robot fish in every possible position relative to the leader, and then compared energy consumption to swimming alone.
"Vortex phase matching"
The results showed a clear difference inpower consumption of robots that swam alone and robots that swam in pairs. They found that the reason for this is how the fish in front affects the hydrodynamics of the fish in the back. The energy consumed by the stalking fish is determined by two factors. It matters whether the follower fish is close to the school leader or far behind, and how the follower adjusts his tail kicks to use the vortexes created by the leader.
Turns out the secret to saving energy isin sync. That is, the follower fish must match the rhythm of its tail with that of the leader with a certain time lag based on spatial position. The researchers called this strategy "vortex phase matching." When the followers are close to the leader fish, the most energetically effective way to do this is to synchronize the tail kicks with the leader. But as followers lag behind, they must get out of sync, lagging more and more behind the leader's tail beats.
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