Fish swimming together is a phenomenon known as shoaling. Shoaling is a behavior in which fish gather together in a group for protection and social interaction. This behavior is seen in many species of fish, including freshwater and saltwater varieties. Shoaling can also be seen in other aquatic animals such as jellyfish and squid. Shoaling is an important part of the life cycle of many fish species, as it provides protection from predators and helps them find food more easily.