The pacu fish, known to bite off male swimmers' testicles, has also been found in Sweden.
A testicle-eating fish nicknamed the "ball-cutter" could be swimming towards the UK after being found in French waters.
The razor-toothed pacu fish, which has been known to bite off male swimmers' testicles, was spotted in the River Seine in Paris.
French police took a photo of the beast normally found in the Amazon, and said it measured 1ft.
The South American species was also seen in Sweden last month when a fisherman hooked an eight-inch specimen in the Oresund Sound, and prompted a warning to men to keep their trunks on when heading for a dip.
The pacu can grow up in 35 inches and weigh up to 55lb in their natural habitat in the Amazon basin and Papau New Guinea.
They are very similar to a piranha fish, but have flatter, stronger teeth designed for crushing, and fisherman have reportedly bled to death after having their testicles bitten off.
Fish expert Henrik Carl said the pacu was not normally dangerous to people but it has got "quite a serious bite".
He said: "There have been incidents in other countries such as Papau New Guinea, where some men have had their testicles bitten off."
"They bite because they're hungry, and testicles sit nicely in their mouth."
"It normally eats nuts, fruit and small fish, but human testicles are just a natural target."