Just when you thought it was safe to go back into the water, as the saying goes, male skinny-dippers in Scandinavia are being warned about a fish infamous for munching on testicles.

Yes, you read that right.

The Pacu, native to South America, was found by a fisherman in the Danish/Swedish strait of Oresund, according to experts at the Natural History Museum of Denmark.

Though the fish has big teeth and looks menacing, it is generally known as a friendly cousin of the piranha. The Pacu's large teeth aren't as sharp as the piranha's but are "fully capable" of severing fishing lines and fingers, the museum's experts said. Oh yeah, and the Pacu is vegetarian, unlike it's meat-eating cousin.

So why should swimmers beware? Pacu fish love crushing nuts with their powerful jaws and sometimes can mistake the male reproductive organs for their favorite snack.

Just how the exotic fish ended up in Scandinavian waters is a bit of a mystery, the museum said.

"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.

Museum experts said they are going to perform a genetic examination on the Pacu found in the fisherman's nets to learn more about the fish.

Meantime, the advice of the museum's experts is this: "Anyone choosing to bathe in the Oresund these days had best keep their swimsuits well tied."

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