The Pacu (Portuguese pronunciation: (paˈku) is a common name used to refer to several common species of omnivorous South American freshwater fish that are related to the piranha. Pacu and piranha do not have similar teeth, the main difference being jaw alignment; piranha have pointed, razor-sharp teeth in a pronounced underbite, whereas pacu have squarer, straighter teeth, like a human, and a less severe underbite, or a slightoverbite. Additionally, full-grown pacu are much larger than piranha, reaching up to 0.9 m (3 feet) and 25 kg (55 pounds) in the wild.Pacu is a term of Brazilian Indian origin. When the large fish of the Colossoma genus entered the aquarium trade in the U.S. and other countries, they were erroneously labeled pacu. 

 

Pacus inhabit most rivers and streams in the Amazon and Orinoco river basins of lowland Amazonia, where they form part of the highly diverse Neotropical fish fauna. They have also recently been found in the riverine systems of Papua New Guinea, where it is believed the fish has been introduced to aid the local fishing industry. In August 2013 a Pacu was discovered in Scandinavian waters, a fisherman pulled a 21 cm (8.27 inch) specimen from Øresund Sound off Sweden's south coast.[5] An angler fishing on the river Seine in Paris, France caught a Pacu on 30 August 2013.