How do fish swim in schools?

If you’ve watched Blue Planet – or even seen Finding Nemo – you’ll have seen fish swimming together as a group, with every single fish heading in the same direction at the same time.

Not to be confused with a shoal, which is where fish of the same species swim together but in different directions forming a social group, a school is where fish of the same species work and swim together as one group. Schools of fish vary in number, ranging from just four to hundreds and even thousands in the wild. 

Research suggests that many species of fish have evolved to swim in schools for several reasons: to protect themselves from predators (it’s much harder to attack a group of fish together than one on its own), to increase their chances of finding food, and to swim more efficiently. Researchers believe that the close proximities between the fish in the school mean that it’s much easier to swim, similar to the way that cyclists make use of slipstreams in a peloton to conserve energy. 

This efficiency has captured the imagination of engineers. Most commonly robots are programmed to operate together in a school-like formation to problem solve or complete a task more quickly.

The influence of schooling fish has also made it to surprising places. In 2010 engineers at the California Institute of Technology (Caltech) took inspiration from the flow behaviour of water left in schools’ wake to design the layout for a wind farm. The design proposed using vertical axis turbines, which look like giant, upright, spinning egg whisks, that turbulent winds bear down on from different directions. Engineers had studied the whirling masses of water, called vortices, left behind by fish swimming in a school. They noticed that some rotated clockwise, while others rotated counterclockwise. The design planned to arrange the wind turbines based upon the vortices shed by schooling fish to maximise energy generation. These principles continue to underpin work carried out by the Caltech Field Laboratory for Optimized Wind Energy (FLOWE), which demonstrates innovative approaches to wind energy that have the potential to concurrently reduce the cost, size, and environmental impacts of wind farms.

More recently, in April this year, engineers at Johns Hopkins University discovered that a school of fish make less sound than a solitary swimming fish. Their findings could inspire the design and operation of much quieter submarines and autonomous undersea vehicles. To simulate different numbers of fish swimming, the researchers created a 3D model showing variations of between one and nine fish being propelled forward by their tail fins. They changed formations, the closeness between the fish as they swam, and the synchronisation of their movements. 

They discovered the synchronisation of the group’s tail flapping – or lack of – was a vital component in reducing the sound of the school as it swam. If fish moved their tail fins at the same time, the sound added up and there was no reduction in overall sound. But alternating tail flaps cancelled out each other’s sound. The team also noted that these same sound-reducing tail fin movements are key to lessening friction between the fish, allowing them to swim faster while using less energy. 

From more efficient wind farms to quieter underwater vehicles, the influence of nature – in the case the behaviour of schools of fish – on technological advances is clear to see.