Look closely at this photograph of a moorish idol (Zanclus cornutus) and you will see the lateral line running along the moorish idol’s body in the the center, white-yellow vertical stripe.
They provide a sense to fish which humans do not have. They are composed of tiny sensory hairs that pick up small variations in water movement, providing fish with better spacial awareness which helps track prey and detect the approach of predators. Lateral lines also provide fish with orientation when shoaling and schooling.
In scientific experiments conducted in a 1976 study by Partridge Pitcher, fish were removed from a school and deliberately blinded. They were then released back into the school and were able to resume their schooling behavior due to having lateral lines.