A study published in Nature Communications highlights a new explanation of how fish swim in schools, a technique they use in order to save energy. The research comes from scientists led by Professor Xie Guangming in the College of Engineering at Peking University.
It has been assumed that fish swim in schools in order to save energy, in the same way, that it has been proved that birds fly in flocks in order to reduce drag and be more efficient. But while there was one theory proposed by engineer Daniel Weihs in 1973 regarding the energy-saving strategies used by fish, there is still debate over the actual physics behind the question.
In order to test the theory of whether fish save energy by swimming in schools, Professor Xie's group designed a bio-inspired robotic fish that would mimic the natural motion of fish in the wild. Then, using groups of these robotic fish in an ocean-mimicking tank, they ran more than 10,000 trials on collective swimming.
From these experiments, the team determined that a “follower” fish can save energy by adjusting its body movement relative to the leader. They tested this rule on real fish at the Max-Planck-Institute of Animal Behaviour, Germany, collaborating with Professor Iain D. Couzin’s lab to analyze the relationship between the formation and relative undulations of fish bodies. Interestingly, they found that real fish did not even depend on their vision or lateral line perception in order to make these adjustments.
“We find that followers, in any relative position to a near-neighbor, could obtain hydrodynamic benefits if they exhibit a tailbeat phase difference that varies linearly with front-back distance, a strategy we term ‘vortex phase matching’. Experiments with pairs of freely-swimming fish reveal that followers exhibit this strategy and that doing so requires neither a functioning visual nor lateral line system,” write the authors.
The implications of this discovery are two-fold, for both biologists and engineers. Firstly, biologists who want to explain the reasons behind the phenomenon will be excited by the potential that this mechanism has to show up in other biological systems, especially because the team proved that fish don’t need to complex perception and brain processing to adhere to the rule. Secondly, engineers may be able to use this knowledge to design control algorithms for bioengineering industries, such as in underwater robots, for instance.