The pacu is feared by fishermen in its native South America for its powerful jaws, which can "rip off a man's testicles with a single bite", earning it the nickname "The Nut Cracker".
However, fish may have an unfairly bad rap.
According to Wikipedia, the testicle-biting claim is erroneous and originated in Denmark, where a fisherman caught a pacu in 2013.
The catch led to media reports mistakenly warning that the fish could attack male testicles but the reports were based on a joke.
The pacu is a popular pet when young but tend to get dumped in public waterways when they grow too big. The species has also turned up in rivers and ponds across the US, Europe and even Papua New Guinea after being dumped by thoughtless owners.
The fish are popular in pet stores as juveniles, but can reach up to 30cm in length, outgrowing most home fish tanks.
Fishermen are encouraged not to release pacus back into the water because they are considered invasive.