The appearance of a Brazilian fish has sent a chill through summertime swimmers in Sweden and Denmark. The alarming fish isn't the much-feared piranha but its cousin, the pacu, which has large teeth and a reputation for attacking men's testicles.
A wild pacu was caught this month by amateur fisherman Einar Lindgreen in the Øresund Sound, a body of water that separates Sweden and Denmark, according to the Natural History Museum of Denmark in Copenhagen, which sits along the sound's coastline.
Museum expert Henrik Carl explained the potential danger posed by the fish to Sweden's The Local, saying the pacu's "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."
Danish experts recommend that "anyone choosing to bathe in the Øresund these days had best keep their swimsuits well tied." But Carl is also quick to say that a swimmer is more likely to drown than to be bitten by a pacu. Researchers aren't sure how many of the fish are in their waters.
"Discovering whether this fish is a lone wanderer or a new invasive species will be very exciting. And a bit scary. It's the first time this species has been caught in the wild in Scandinavia," says Carl's colleague Peter Rask Møller, another expert from the museum.
Last summer, a pacu was found in an Illinois lake; in 2011, a pacu was blamed for the death of two men in Papua New Guinea, where it is reportedly nicknamed "the ball cutter."
British fisherman Jeremy Wade managed to catch one of the fish in Papua New Guinea, a feat he says was made difficult by the pacu's shyness and elusiveness. Here's how he described it to The Daily Mail:
"When I reeled it in, it had this mouth which was surprisingly human-like, it is almost like they have teeth specially made for crushing.
"They are like human molars and the fish have powerful jaw muscles. They are very deep bodied and solid like a carp, with strong muscles."
The fish Wade caught weighed 40 pounds; pacu can reach more than 55 pounds, according to the University of Copenhagen.
In the past, the fish's appearance outside its native habitat has been blamed on aquarium owners and fish farmers — in addition to its frightful reputation, the pacu is known for having a mild, slightly sweet flavor. A 1997 U.S. academic study found the taste to be "comparable to that of hybrid striped bass, tilapia, and rainbow trout, but superior to catfish."