If you're male and planning a swim off the coast of Sweden any time soon you might want to reconsider.
For a fearsome fish with a penchant for feasting on human testicles has been spotted in Öresund Sound, The Telegraph reports.
The pacu fish is a relative of the piranha and until now had never seen in European waters.
The pacu is a relative of the piranha (pictured)
In this case, a 21 cm specimen was reeled in and confirmed, prompting the National History Museum in neighbouring Denmark to issue the following warning:
"Keep your swimwear on if you're bathing in the Sound these days - maybe there are more out there!"
The freshwater fish, which hails from the Amazon, can grow up to 90 cm in length and weigh up to 25 kg. It primarily feeds on nuts, aquatic vegetation and snails, but its habit of attacking male genitalia has seen it dubbed 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," Henrik Carl, a fish expert at the Danish museum, told The Local.
"They bite because they're hungry, and testicles sit nicely in their mouth. And its mouth is not so big, so of course it normally eats nuts, fruit, and small fish, but human testicles are just a natural target. It's not normal to get your testicles bitten off, of course, but it can happen, especially now in Sweden."
In further incidents of pacus turning up unexpectedly, last year one was discovered in Lake Lou Yaeger in Illinois, KSDK reported.
In 2011 British fisherman Jeremy Wade travelled to Papa New Guinea to catch his own "ball-cutter" after learning one had castrated two fishermen who had subsequently bled to death.
He told The Metro: "When I reeled it in, it had this mouth which was surprisingly human-like, it is almost like they have teeth specially made for crushing."