If you want to hold onto your nuts, you may want to avoid swimming in waters infested by the Pacu, a relative of the piranha that's known to have a taste for human nuts. The Pacu is native to South America, but a specimen was recently found by fishermen in the strait of Oresund between Denmark and Sweden, prompting experts in Denmark to warn men to keep their swim clothes on when taking a dip in the sound.
The Pacu is generally a vegetarian. It eats nuts (from plants) and fruit and also small fish. It is not normally a threat to people, but after being introduced to Papua New Guinea two decades ago to increase fish stocks there, it became notorious for its taste for human testicles. There, it was nicknamed the "ball cutter," because as Henrik Carl, a fish expert at the Natural History Museum of Denmark explained to 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," he added.
It is believed the fish was released into Scandinavian waters by a fish collector. Pacus have also been found in several U.S. states, including Texas. It is almost identical to the piranha, except that it has humanlike teeth and lacks the latter's severe underbite.