Fish perform this phenomenon for a number of reasons. The first is to support social and genetic functions, aggregating together to increase the ease of communication and reduce stress – experiments have shown that heart rate reduces significantly in shoaled fish compared to those alone. The second advantage of schooling is to boost the group’s foraging success, which has been proven in trials to grow considerably in comparison to a solitary specimen. This is simply because the number of eyes looking for food increases dramatically and, partnered with the ability for each fish to monitor the behaviour of those around it, means that when one fish demonstrates feeding behaviour, the others follow.
Finally, the third – and primary – reason why fish school is for protection. By grouping into a tight, regimented pattern, the fish minimise their chance of being picked off by generating a sensory overload to a predator’s visual channel. The swirling mass of twisting silvery fish creates a blending effect where the predator struggles to track a single target and becomes confused.