Yes, it is the fact of life that piranhas eat animals. I see noting wrong with feeding them what they would consume in the wild but there is one problem. The mouse (it seems) was one of the frozen ones you buy at the big box pet shops and while they are alright once in awhile, there is no way to tell what went into the mouse before it was given to the fish. In the wild a mouse would be eating all sorts of nutrients that could in turn be passed on to the fish. Good right? In this case the mouse was bred to be food. The company that breeds them (depending on which one) is trying to push out as many as they can for as cheep as they can so those nutrients that wild fish would get are not there for your fish. With this in mind it would be better to either raise your own food (please no videos) or buy prepared food that contains the needed vitamins and minerals. An alternative to mice that is not bloodworms are eathworms. Many people feed them to large fish and bait shops have them for very little cost, plus it would keep some of that same interesting bahavior that you clearly like to see.
