A Pacu, a cousin to the meat eating piranha, was caught in a Danish river for the first time ever, baffling experts. Although the species of fish is not to be feared like its infamous relative, scientists are cautioning male swimmers to “protect their privates.”

Pacu
A Pacu was found in the waters of Denmark. Henrik Carl

The Pacu have a similar appearance to piranhas, with sharp teeth jutting out of its mouth, but are mostly harmless to humans. Native to South America, the fish is found elsewhere, including in parts of the United States, mostly introduced into the wild by hobbyists or the fishing industry. The species of fish is an omnivore, eating almost anything, but mostly sticks to a vegetarian diet.

The first Pacu found in Denmark was caught by Einar Lindgreen, a local fisherman, in the strait Oresund, reports the University of Copenhagen. Lindgreen found only one Pacu in his nets and experts are not sure if it was an isolated incident or could be part of a larger problem. Peter Rask Møller, from the National History Museum of Denmark at the University of Copenhagen, said in a statement, “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.”

Experts believe the fish may have come from an aquarium owner or from fish farming. Denmark’s Aquarium, The Blue Planet, gets its water from the Oresund but the aquarium’s curator, Lars Skou Olsen, denies it could have come from their location. The aquarium says their Pacu are much larger and there are several filter systems in place to avoid any fish from escaping into the Oresund.

Møller believes an aquarium owner dumping the fish into the Oresund is the likely culprit. “It is not unlikely that someone has emptied their fish tank into a nearby stream just before a vacation and that the Pacu then swam out into the brackish waters of Oresund,” said Møller.

Pacu, in the wild can grow to weigh as much as 25 kilograms, 55 pounds, and are considered an invasive species in the United States and Asia, notes the university. The fish will eat almost anything, including small fish, but their diet consists primarily of fruit and nuts. There have been reports of Pacu biting a finger off, and their human-like teeth are capable of snapping fishing lines.

While swimming in the strait should be safe, experts warn men to make sure their bathing suits are securely fashioned. According to the university, there have been reports from Papa New Guinea of Pacu mistaking a man’s genitalia for their preferred nuts, making swimming a precarious situation.