Former owners of these fish released them into the wild, changing the natural eco-system of the area. " The fish are red-bellied pacus (Piaractus brachypomus) and are piranha relatives, though their diet is mostly vegetarian. Pacus are popular with aquarium owners for their unusual square teeth that look remarkably human —rather disturbingly so, in fact. But recently, pacus have been sighted in places where they shouldn't be: Lake St. Clair and Port Huron in southeastern Mich