A school of fish is a vivid demonstration of synchronicity. However, centuries of research have left the main question unanswered: why do fish move like this? Do they save energy by swimming in schools? An international team of scientists gave the answer by conducting an experiment involving biomimetic robots. The research results are published by the journal Nature Communications.
Using biomimetic robots similar to fish, the researchers found that fish that move in schools can use the eddies created by those in front. It turned out that robots get hydrodynamic benefits from the closest neighbor in the jamb no matter where they are located. This is due to the “vortex phase matching” strategy. Such a rule for the behavior of fish in a school was previously unknown.
“Shoals of fish are highly dynamic social systems,” 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 of whether a fish can save energy by 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 with theoretical models and predictions.
The new study, however, has overcome this barrier 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 trials, 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 in power consumption between 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.
It turns out the secret to saving energy is syncing. That is, the follower fish must match the rhythm of its tail with the rhythm 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.