Piranha

A piranha is a member of a family of omnivorous freshwater fish which live in South American rivers. In Venezuelan rivers, they are called caribes. They are known for their sharp teeth and a voracious appetite for meat.
Piranha have a reputation as a fearless fish who hunt their prey in ferocious packs. However, recent research, which "started off with the premise that they school as a means of cooperative hunting", discovered that they were in fact rather fearful fish, like other fish, who schooled for protection from their predators, such as cormorants, caimans and dolphins. Piranhas are "basically like regular fish with large teeth".