People get these pets like fish and reptiles and they get tired of taking care of them. So instead of finding someone to take them or disposing of the properly they release them into the wild, where they dont belong. You hear about pacu and piranah being caught in Ohio about this time every year. Most wont survive because of the winter temps here but some may. Its just like that idiot who released his alligator out in California, they named it "Reggie". It was on the loose for 2 years before they finally captured it.