Swimmers warned of testicle-biting pacu fish

Swedish men are being cautioned against nude-swimming after the discovery of a fish known for biting human testicles.

The Natural History Museum of Denmark issued the warning after a local fisherman caught a pacu fish, a relative of the piranha, in an eel trap in the Oresund Sound off the country's south coast.

"Keep your swimwear on if you're bathing in the Sound these days - maybe there are more out there," the musuem's warning read.

According to Sweden's The Local, the pacu is usually found in warmer waters and has a global reputation for biting human 'bits'.

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

Although pacu generally feast on nuts, fruit and smaller fish, Carl called human testicles swimming in the water a 'natural target'.

"They bite because they're hungry, and testicles sit nicely in their mouth," Carl explained.

According to The Local, pacus have reportedly killed fisherman who bled to death after losing their testicles.

The pacu fish that was caught caused no harm to swimmers or fishermen.

Carl said the risk to other swimmers is minimal, too.

"No, there's nothing to worry about," he said.

"You're more likely to drown than get your nuts bitten off."

"It could become a problem some time in the future if it's not the only one. This one was the first, but who knows, it's probably not the last," he added.

The pacu fish is native to South America.