A sharp-toothed, testicle-biting cousin to the piranha has been pulled up by a woman fishing in Lake St. Clair, located near Detroit, Mich. The fish measured around two feet in length and weighed 15 pounds, according to Tech Times.
The fish is the pacu, a vegetarian who, although it prefers fruits and nuts that drop into the Amazon River and its tributaries, has been known to confuse nuts for human flesh. The pacu caught in Michigan was caught on a hook that was baited with a nightcrawler and catfish.
In Papua New Guinea, where the pacu has also escaped, it is believed to have mistaken male reproductive organs for nuts. Two fishermen were reportedly were bitten and bled to death in 2011, according to Jeremy Wade, host of Animal Planet's "River Monsters."
The same Amazonian nut-cracking fish was caught in Oresund Strait between Denmark and Sweden last year and, in 2012, found in a lake in Illinois.
Despite past reported incidents, one Amazon fishing guide says the pacu is not aggressive, but is good to eat.
"I like to pan fry it, or bake it," said Anthony Giardenelli, owner of Otorongo Expeditions, a tour company that takes trips throughout in the Peruvian Amazon. "It's very tasty," he said by phone from his office in Iquitos.
Giardenelli has caught dozens of pacu fish each season as the floodwaters of the Amazon drive fish into the forest in search of food.
"They have evolved migrating in and out of flooded waters to eat fruit and nuts," Giardenelli said. "They are attracted to anything splashing. Rubber tree seeds are one of their favorites. They are very hard-wired to follow a plopping noise in the water."
Giardenelli says he has heard the sound of pacu cracking nuts under water from a boat on the surface. "It sounds like two pool balls clacking together," he added.
Experts believe the pacu could be spreading to these other waterways around the world by hobbyists who dump the fish overboard when they get too big for the home aquarium.
"It's a plant eater," said Stefan Tanner, an editor and translator at Amazonas Magazine. "If you release it in Denmark, it won't survive the winter. If you release it in Florida, it may swim for a long time. Will it reproduce? That's another question."
Giardenelli says that he has never heard of the pacu biting a human in its Amazon homeland. Perhaps it was hungry when transplanted somewhere else.
Giardenelli says he worries about the bite of a much more dangerous fish in the Amazon. That's not the piranha, but the candiru, or parasitic toothpick fish. Although not confirmed by scientists, there are reports that the candiru is attracted to urine and has attacked unsuspecting bathers through the urethra.
Editor's Note: An earlier version of this article appeared on Aug. 13, 2013.