The Pacu Fish

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 don't have similar teeth, although the main difference is 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 slight overbite.[1] 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. In the Amazon, the term pacu is reserved to smaller and medium sized fish in the Metynnis, Mylossoma and Myleus genera. The Colossoma macropomum fish are known as tambaqui, whereas Piaractus brachypomus is known as pirapitinga.
These fish are rumoured to bite human testicles, earning it the nickname "ball-cutter"
source: wikipedia