I have an empty 55 (I think it's 55 anyway) gallon tank its 4 foot long, 21 inches tall, but only 12 inches wide . I'm assuming 12 inches wide is probably too tight for any piranhas, but I don't really know. If I can't do piranha I'll be looking into mabye some type of african cichlids, my only issue with them tho is that all the ones I've seen always hang near the bottom of the tank and that seems like a bit of a waste of space in such a tall tank if they're all gonna hang out near the bottom all the time. If I can't have piranhas I want a more filled out tank with lots of colorful and decent sized, active fish. Any suggestions?