'Ball cutter' fish nothing to fear, expert says

A fish with a toothy bite does not have a taste for male genitalia, a Danish fish expert is assuring nervous Scandinavian swimmers.

Pacus with nutcracking jaws can grow to almost a metre long

A pacu, front left, swims with other fish in its tank at the Cleveland Metroparks Zoo in January 2012. (Amy Sancetta/Associated Press)

A fish with a toothy bite does not have a taste for male genitalia, a Danish fish expert is assuring nervous Scandinavian swimmers.

Earlier this week, following the first discovery of a pacu in waters between Denmark and Sweden, Peter Rask Moeller of the National History Museum of Denmark jokingly suggested that Scandinavian men should be wary when going for a dip because of the fish's strong bite, which has earned it the nicknames of "ball cutter" and "nutcracker fish."

Part of the Pacu's diet includes nuts. Couple that with an unverified story of the fish with the powerful bite castrating some men in Papua New Guinea, and it was enough to cause a media buzz that could drive some men out of the water faster than the theme music from Jaws.

But Moeller has since clarified that the fish, which is a South American native related to the piranha and can grow to measure about a metre long and weigh 20 kilograms, is unlikely to even be encountered in Scandinavia.

"All we said last week (with a smile) was that male swimmers should keep their pants on in case there are more pacus out there in our cold Baltic waters," Moeller told National Geographic in an email.

"Its teeth and powerful bite can for sure be dangerous, but to meet one here and [have it bite you] is highly unlikely, of course."

"They fear humans and will try to escape."

Lars Skou Olsen, the curator of Copenhagen's Blue Planet Aquarium, said swimmers need not be worried.

"They will be lucky if they see [a pacu]," he told National Geographic.

Reports of a taste for testicles aside, the discovery of the fish near Denmark does have experts pondering. Moeller says no one thought a pacu could live in cold salt water.

"That this fish thrived in the seas is a mystery," he told National Geographic.

The fish is sold legally in Denmark, leading Moeller to theorize it may have been released from a home aquarium.

There have been many reports of red-bellied pacus showing up in U.S. lakes and rivers.