Warning to Swedish Men: Don’t Swim in the Nude, Testicle-Eating Fish Caught in Oresund Sound (VIDEOS & PHOTOS)

Skinny dipping has its risk, several South American fishermen have discovered after their testicles were attacked by the pacu fish, a relative of the piranha.

News.com.au reported that Swedish men have similarly been warned recently not to go swimming without their trunks on or risk having their balls as the pacu fish's dinner, following a 21-centimetre pacu being caught by fishermen in the Oresund Sound last week. The fish, caught off the Swedish coast, is undergoing DNA tests to confirm its identity.

"Keep your swimwear on if you're bathing in the Sound these days - maybe there are more out there," Swedish news site The Local quoted Henrik Carl, fish expert at the Danish museum.

"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," he explained.

The newspaper cited previous reports of fishermen bleeding to death following the fish testicle attack. The fish could grow up to 90 centimetres and weigh up to 25 kilogrammes.

The pacu fish is native to the Amazon and Orinoco basis, but had been spotted also in Papua New Guinea, Lake Lou Yeager in Illinois and Texas. Officials in Texas are said to have placed a $100 reward money for anyone who could catch the testicle-eating pacu.