Fish travel in schools because they are programmed by evolution to know that safety lies in numbers. Should a hungry predator approach the group, the first line of defense begins with the many confusing silvery flashes or mesmerizing stripes that make it difficult to focus on a single fish. Schools also seem to make finding food an easier task. And some fish schools are more like street gangs, patrolling their territory and running out any trespassing intruder.
For more information, please read Why Fish Swim in Schools.