Do these make good aquarium fish overall? More or less needs compared to oscars? As I said in another thread, I was thinking of getting oscars, but I've done some looking and it seems piranhas need less space per fish. If so, I could add more than 2 like with the oscars. Anyone ever had a group of these? Do they thrive on fish food of some kind? If they need live food all the time that's a deal breaker.