Mark: I had two Red bellied Pacu's, in a 35 gallon tank, years ago. They are, in the Piranha's family, but are not vicious. They did have those scary teeth, though. Can you imagine the Fake News, reporting about Killer Fish, in the water I do like Dave's idea, of the Alligators.
You'd have to put them on leashes so they didn't stray over on the WetBack side, the Cartel would be having Gator Kabobs or worse like convincing the Gators into being drug mules, I could see the Border Patrol stopping a Gator and checking it for drugs!
Mark