A group of fish is called a "school" or "shoal," depending on their behavior. A school typically refers to a group of fish that swim together in a coordinated manner, often for protection from predators or to optimize their feeding strategies. Shoaling fish tend to swim loosely together, without synchronizing their movements as strictly. Both terms highlight the social behavior exhibited by fish in various environments, influencing their survival rates and energy efficiency during movement, as well as their ability to find food.