Schools of fish are composed of individuals of a similar size that swim in the same direction in order to confuse their predators.

For this strategy to be effective, the fish must constantly be aware of the position and speed of the other members and they achieve this thanks to their evolved vision that detects the silvery flashes of the scales. 
They also have a system of lateral lines located on the side of the body composed of cells capable of capturing vibrations generated by water, thus detecting the speed and direction of their companions around them.