Imagine having tiny sensors all along your body so you could feel the slightest changes in air pressure. That’s roughly how fish notice pressure changes in the water. How do fish stay together in schools?
From large tuna in the ocean to tiny minnows in a pond, many species of fish swim together in groups, This is what scientists call schooling. The school might contain just a few fish, or it might have millions of members. The fish swerve and turn together in a split second. They neither collide nor scatter apart.
Fish do that by using two senses to maintain the spacing in a school. Fish use their vision and another sense — that humans don’t have –called the “lateral line system”. The lateral line system — sometimes called the “sense of distant touch”– runs all along the sides of a fish’s body. It’s sensitive to vibrations in the water. That’s how fish can sense the direction of water movements made by tails of fish in front and next to them. It allows the fish to quickly detect changes in water pressure made by approaching rocks or seaweed — or even very low-frequency sounds. The fish then decides to speed up, slow down or change direction.
As in a flock of birds, there’s no leader. The movement of the school is the sum of individual decisions. When fish are hungry and safe, the school may disperse to feed. But at the approach of a predator, stragglers quickly rejoin the group — or risk getting eaten.
To better understand how schooling works, researchers tried to model schooling on a computer, using a set of rules based on forces of varying strength of attraction and repulsion. They were actually able to see some schooling in computer fish.
Fish are born with the ability to school. But very young fish, who are too small to swim against a current, often don’t school. Scientist think that’s because their muscle and nervous systems are not yet developed enough. As fish grow into what is roughly analogous to the teenage stage, they are more likely to school. As they get older and bigger still, and there is more competition for food, many species spend less time in a school.