Authorities warn skinnydippers as the Pacu, the testicle-gnawing fish were recently spotted in the Danish/Swedish strait of Oresund.

Known as the cousin of piranhas, these South-American vegetarian creatures can grow as heavy as 55 pounds and have very dangerous teeth. While they do look angry, they're actually kinder than their piranha relatives but not until they see testicles. Apart from being vegetarians, they are a big fan of snacking on real, edible nuts, which is why it isn't much of a surprise that they will also go for men's sacs.

While they are cousins, the Pacu fish have a number of differences compared to the piranhas. The South-American natives are known to have a more square, straight teeth while the piranhas have razor sharp sets. The Pacu can grow bigger than its cousin, reaching over 3 feet in size.

There have been reports that Pacu bit off skinnydippers' nuts from Papua New Guinea. Now, the warning comes after local fishermen caught a Pacu in the waters between Sweden and Denmark. While it's still unknown as to how exactly these gnawers got to the Nordic region, authorities from the Natural Museum of History are warning men to "keep your swimsuit on in the sound these days, maybe there are a few more out there."

"They bite because they're hungry, and testicles sit nicely in their mouth," fish experts inform. Pacu are known to chew on skinnydippers' testicles around the world. In fact, they have been dubbed as "ball cutters".

Experts are speculating that an amateur aquarium owner may have let out the Pacu out into the open sea. Until now, authorities have yet to find out how many there really are out there.

So hear us out, boys, when we tell you to keep your pants (or swimsuit) on.