A Danish fisherman made an unusual find in his nets recently when he discovered a pacu, a sharp-toothed cousin of the South American piranha with a reported penchant for testicles.
"If they bite, they can bite hard ... especially when they bite you where you really don't want to be bitten," joked fish expert Peter Resk Moeller of the Natural History Museum of Denmark.
However he said that the pacu is not a meat-eater and normally does not attack people.
The rare find has spread across international media, who have jumped on the fish's reputation as a "ball-cutter" for its reported attacks on men.
In a documentary for US channel Animal Planet in 2012, an expert on extreme fishing relayed anecdotally that some fishermen in Papua New Guinea had had their testicles bitten by pacus.
However Moeller defended the toothy vegetarian's eating habits.
"The fisherman was very surprised and a bit suspicious because this fish, the pacu, looks so much like a piranha but it is not a carnivore," said
It is not known where the fish came from, but Moeller suggested "it probably came from a local aquarium."
"It's interesting to see that it survived in the Oeresund (Strait that separates Sweden and Denmark). Even if the water is not very salty we didn't know it could survive the salt," he said.
Moeller said it was hard to predict whether the pacu would now become common in Danish waters.
"Every time we have a fish of a new species you think you won't find another one, but you never know."
The fish is however farmed in North America as food.
"I've heard it's very good, I would like to try it," Moeller said.
Explore further: No-take marine reserves a no-win for seahorses