It's happened before on Priest too.
https://www.youtube.com/watch?v=XT50j_wr1ro
I can't tell if that's a Pacu or Pirahna, can't see the teeth. Either way, it's definitely not supposed to be in there. This happens when people release their pets in the lake. I seem to recall confirmed cases of Pirahna caught in our lakes but forget which lakes.