Pacu Fish Eat Testicles In Sweden: 4 Things To Know About The South American 'Ball-Cutter' [VIDEO]

Male skinny-dippers in Scandinavia need to be wary, as a fish notorious for biting testicles has been found in the waters. The Pacu, a fish native to South America, was discovered by Danish/Swedish fisherman in the strait of Oresund.

According to the Natural History Museum of Denmark, the fish has big menacing teeth but is not as dangerous as its cousin: the piranha. But that's not to say the teeth aren't capable of damage -- the teeth can sever fingers and fishing lines according to museum experts. Oddly enough, the Pacu is a vegetarian fish. So why is the fish biting male testicles? The fish has a penchant for crushing nuts with their teeth and mistake testicles for nuts.

In fact, according to Metro, two fisherman reportedly died of blood loss in Papua New Guinea after a Pacu munched off their testicles. The incident earned the Pacu the nickname of the "ball-cutter."

"The pacu is not normally dangerous to people but it has quite a serious bite, there have been incidents in other countries, such as Papua New Guinea where some men have had their testicles bitten off," said Henrik Carl, a fish expert at the museum, to The Local.

The museum notes that the real mystery is how the South American fish made its way to Scandinavian waters and to find an answer, the museum will be performing a genetic examination of the Pacu found in the fisherman's nets.

"Amateur aquarium owners and fish farmers are "the usual suspects" when we meet fish where they do not belong," said the museum's Peter Rask Moller.

Here are four things to know about the Pacu fish:

1. Pacu fish can grow up to 55 pounds.

2. The vegetarian Pacu eats nuts, aquatic vegetables and snails.

3. The Pacu have a strong jaw and teeth for cracking nuts, as the fish is native to the Amazon. Its presence in Papua New Guinea is a relatively new one, as the fish was introduced to the environment 15 years ago to increase stocks.

4. The Pacu looks just like the piranha.

"They are almost identical to the piranha, you couldn't even tell from the outside," said Carl. "It's just that they have different teeth. Flatter and stronger, perfect for crushing."