The rumor spread rapidly via Facebook and Twitter postings, e.g.:
News Flash: Piranha's on the loose in Opry Mills Mall! All the salt water fish at the Aquarium Restaurant died during the flood except the Piranha's who are able to live in fresh water and are now swimming around somewhere in Opry Mills Mall.
Thursday's papers confirmed that Opry Mills Mall was under two feet of water and that some of the fish in the Aquarium Restaurant's 200,000-gallon tank had perished, but said reports of escaped piranhas were untrue.
It's all too reminiscent of a rumor outbreak during Hurricane Katrina in 2005, when sharks and alligators were said to be prowling the flooded streets of New Orleans, feeding on stranded people and lost pets. No actual sightings were ever confirmed.