If you’ve watched the Tour de France or any other professional cycling events, you’ll have seen cyclists riding behind one another in a paceline or peloton to enjoy the benefits of drafting. These formations help to shield riders from headwinds and reduce drag that would otherwise slow them down.
It seems that schools of fish adopt a similar approach to swimming in rough waters by schooling together. That’s the theory proposed in a recent article in the journal PLOS Biology by zoologists from Harvard, Princeton, and Johns Hopkins Universities. The “turbulence sheltering hypothesis” suggests that by moving collectively, fish save a significant amount of energy compared to swimming on their own.
To test the hypothesis, researchers created a “water treadmill” in a tank containing giant danios (Devario aeqipinnatus), a freshwater minnow species known for their schooling behavior. They added a propeller, allowing them to control the flow of the water and create both calm and turbulent conditions. They also used high-speed cameras and a respirometer to monitor movement, respiration rate, and energy usage.
As one might expect, the researchers found that the fish expended significantly less energy (up to 79% less) when swimming in schools of eight individuals compared to swimming alone. The far more surprising discovery was just how energy-efficient it was to swim in a school. By grouping together more closely, the schooling fish were able to keep their energy usage constant regardless of the turbulence of the water. By contrast, solitary fish had to constantly and vigorously move their tails in rough waters to maintain their speed.
Schooling isn’t a drag for fish:
- Despite their name, giant danios can only reach a maximum size of six inches (15 cm) in length. However, this makes them one of the largest minnows. They are freshwater fish native to the Indian subcontinent and much of Southeast Asia.
- According to lead researcher Yangfan Zhang, while the comparison to humans running or cycling behind one another to reduce drag is valid, the acceleration enjoyed by schooling fish is much greater. “Previous research has shown that fish can even benefit from thrust wake (an increased fluid velocity),” said Zhang.
- The implications of this research could be valuable for further studies on fish ecology and hydrodynamics, and for improving our understanding of the habitats best suited for schooling fish.
- Traveling in schools is likely to confer other evolutionary benefits besides locomotion efficiency, including more effective hunting and foraging, increased likelihood of finding a mate, and protection from predators.
- Not all fish species shoal (the term for fish grouping together for social reasons) or school (moving in a coordinated manner). Around half of species shoal for part of their lives, while one-quarter spend their entire lives in shoals.
