A group from the College of Engineering at Peking University explains how schooling fish conserve energy in a collective motion.
The collective behaviour of certain animals has piqued the interest of many biologists for many decades. One example is how geese are known to fly in a “V” formation or a “dash” formation during long-distance migrations to reduce drag and save energy. This phenomenon is also observed in fish that swim in schools, begging the question as to whether this is also to conserve energy within the school.
Since Daniel Weihs (1973) proposed a possible energy-saving mechanism for schooling fish, the investigation of energy-saving mechanisms in collective underwater swimming has attracted a long and widespread interest among biologists and roboticists. What interested biologists were the mechanisms behind this natural phenomenon, and roboticists hope to leverage on this understanding of the mechanism to learn and apply to the field of engineering. However, it is still not known whether, and if so, how, schooling fish can save energy by interacting with the vortices shed by neighbours.
In a research published in Nature Communications, by a group from the College of engineering at Peking University, led by Professor Xie Guangming, they used the high-fidelity bio-inspired robotic fish developed by themselves as a physical experimental model to explore the mechanism.
Over ten thousand trials on collective swimming was conducted on robotic fish in the low-turbulence flow tank platform at the State Key Laboratory of Turbulence and Complex Systems in Peking University. It was found that a simple rule could explain how the follower can save energy by adjusting its body undulation relative to the leader.
In order to verify whether this rule is also adopted by real fish, Professor Xie’s group, together with Professor Iain D. Couzin’s group at the Max-Planck-Institute of Animal Behaviour, Germany, analysed the relationship between the formation and relative undulations of fish bodies at different swim speeds, and verified that this simple rule is also used by real fish for saving energy.
In particular, after impairing the vision and lateral line perception in real fish, they found that real fish do not require complex perception and brain processing to adopt this rule, indicating this rule might be universal in biological systems.
These results not only suggest a potential energy-saving mechanism for fish school, but also can inspire roboticists to design control algorithms for underwater robot swarm. [APBN]