It might not might very big, but apparently, it has a big bite. Scandinavian residents were recently warned of a potentially sometimes-dangerous fish lurking in their waters. According to a report from CNN, a species of pacu was dumped into a strait -- a mysterious find indeed that experts are blaming on inexperienced fish owners.

The native South American fish, also known as “ball cutter,” earned the moniker for its frequent attacks on men, particularly in their testicular region. According to experts at the Natural History Museum of Denmark, the fish, a “friendly” relative of the piranha, was first found in the Danish/Swedish strait of Oresund by a fisherman.

While it is unknown how the fish landed in Scandinavian territory, experts claim it is most likely the work of fish farmers or aquarium owners, citing inexperience as a common reason for pacu abandonment. Due to the fish’s dangerous nature, including its powerful jaw, ability to sever fingers and predisposition to chomp down on male organs due to its similar appearance to nuts, male skinny-dippers are being warned of possible attacks. “Anyone choosing to bathe in the Oresund these days had best keep their swimsuits well tied,” said a museum spokesperson, Peter Rask Moller.

The pacu fish last made headlines in June 2012 after one was captured by a fisherman in Lake Lou Yaeger in Illinois. According to the Huffington Post, the fish, which was originally thought to be a piranha, was brought into the Illinois Department of Natural Resources for examination. Despite its removal, locals reported spotting similar fish in nearby waters in weeks to follow.