Im not gonna do a direct quote but i saw someone say that piranha are "safe" in this thread. Thats extremely poor advice. They may not be aggressive if cared for properly, but they are by no means safe and they demand a healthy respect of their potential to cause injury. Anyone who would choose to disregard that does so at their own peril. As far as the ethics of feeding live goes I look at it like this: the pet industry is responsible for the death of millions of animals annually, it is a tragedy but it is also the cost of removing animals from their natural habitats so that we can keep them as pets. Having said that I dont believe that there is any ethical issue involved with feeding piranha any animal sold as a "feeder", the more important question in a keepers mind should be "is it healthy for my piranha?" if the answer to that all important question is yes, then knock yourself out. Trying to gauge what an acceptable level of pain for a feeder animal to endure is an excersize in futility...whether its a monitor lizard chewing up a mouse or a snake crushing the mouse till it dies or a piranha biting it to pieces or a person putting it in a freezer to "humanely" (killing something humanely has to be the most oxymoronical statement ever) kill it who cares? either way it sucks to be the mouse.