Cory Vs Piranha

Big piranhas can bite through wooden oars so it may have been a young one without the necessary power, or a big one just ‘moving it on’ or ‘sizing it up’ then deciding not to eat it. They don’t always eat every fish they encounter.
Even a large Oscar can crunch through a Cory, and they don’t have the razor sharp teeth of a piranha or the jaw power.