The undercover operation, which took place Aug. 21 in West Palm Beach, was set up after an officer saw a notice to sell the piranhas on Craigslist, the South Florida Sun Sentinel reported.
Investigator Jon Garzaniti sent Kristina M. Dempsey, the seller, a text message asking whether they could meet to make the deal for a total of $60.
The two planned to meet in a Walmart parking lot. After the deal went down, Garzaniti identified himself as an officer and called for back up.
Dempsey was given citations for possession and sale of a prohibited non-native fish and sale of freshwater fish without a dealer's license.
"I'm not irresponsible enough to let them go in fresh water because I have respect for the environment and the ecosystem," Dempsey said Wednesday. "If you do have animals like this, instead of setting you up and treating you like a criminal, they should offer a way you could hand them over and surrender them if you don't want them anymore."
Evan D'Alessandro, visiting assistant professor of marine biology and fisheries at the University of Miami's Rosenstiel School of Marine and Atmospheric Science, said although piranhas do not pose a threat to humans, they could seriously damage the waterways of South Florida.
"It's not because of their danger to humans, it's because of their danger to the environment," D'Alessandro said. "They are apex predators. They're at the top of the food chain. Our network of canals and freshwater retention ponds and the Everglades is very similar to their native habitat, and they could easily get a foothold."