While it has long been theorized that fishes swim in schools to conserve energy through neighbor-induced flows, as with flocks of birds, the use of robot fishes provides the first conclusive evidence.
A team led by researchers from the University of Konstanz in Germany used biomimetic fish-like robots to observe fish behavior and schools - even directly measuring the energy consumption as an effect of the swirls created by their neighbors. The results of the study demonstrated a phenomenon they called "vortex phase matching." It occurs when a fish adjusts the rhythm of the tail beat to match those in front of them, allowing them to enjoy hydrodynamic benefits.
Details of the study are published in the journal Nature Communications.
Vortex Phase Matching, Measured By Robot Fishes
Researchers simulated the same strategy to the robot fishes, discovering that the force from the water churned by their neighbor in the school was beneficial to them, regardless of their position in the group.
"Fish schools are highly dynamic, social systems," explains Iain Couzin, senior study author from the Centre for the Advance Study of Collective Behaviour at Konstanz, in a university release. Cousin explains that their results explain how swimming in schools is beneficial for fishes, mainly because of these vortices generated by the fishes without the need for maintaining fixed distances.
Despite the energy efficiency benefit in this swimming configuration being proposed before, conclusively determining this hypothesis remained a challenge because of the difficulty associated with measuring the energy expenditure for free swimming fishes. Now, researchers solved the issue thanks to robots. These biomimetic fishes can measure its energy expenditure - comparing solitary swimming to those as a part of a school.
"We developed a biomimetic robot to solve the fundamental problem of finding out how much energy is used in swimming," explains Liang Li, first author also from Konstanz. With multiple of these robot fishes, they can efficiently observe the effect of different swimming configuration to each one's locomotion and energy requirements.
A Robot In the School
Conducting more than 10,000 trials, researchers tested their follower fishes in every possible position in relation to the school's leaders, comparing their energy consumption with swimming alone. Results showed that the leading fishes determine the hydrodynamic behavior experienced by those behind them, allowing them to save energy. Researchers explained that the secret to this increased efficiency lies in how the followers match the beat of the leader's tail flapping.
"It's not just about saving energy. By changing the way they synchronize, followers can also use the vortices shed by other fish to generate thrust and help them accelerate," said Mate Nagy, a co-author in the study.
To further confirm the vortex phase matching among fishes, researchers used an analysis technique with the support of artificial intelligence (AI) to map out the posture of goldfishes as they swam in a group. The AI model was able to predict the behavior of actual fishes using vortex phase matching.
"We discovered a simple rule for synchronizing with neighbors that allow followers to continuously exploit socially-generated vortices," Cousin added.
