Why do fish swim in schools?

Answer 1

fish swim in a school to save themselves from predators. because, predators like shark will not be able to locate a single fish seperately,if the fish are in schools.

Answer 2

Not only to confuse and deter their less vicious predators but, if you've ever heard of the term "safety in numbers" you'll understand that the more targets there are to hit, the less chance there is for one target to actually get caught.

Pretend for a moment that you are a kid with a plan and a water balloon, on top of a building, searching for one specific teacher that you don't like. If that teacher was walking along by themselves it would be rather easy to hit just them. However, if that teacher is walking in a group of other teachers and faculty he/she would be much harder to hit.

Swimming in a school also increases the likelihood that a fish can find enough food to survive and increases the ease of travel one fish has, through whatever body of water it lives in, by use of currents coming off the fins of the fish before it (kind of like the way birds use each other's currents to glide in that "V" formation you can often see when they fly south for the winter).