I was wondering if you can get small piranhas? Ovbiously kept in a tank on there own. As I wouldnt mind a couple in a tank - and the other a community tank of tropical fish.
piranahs need to be in groups otherwise they are scared easily and they arent as exciting as they sound if you have hiding places you will rarely see them untill feeding time and if you dont have enough of them they are shy and scared easily and live food is dirty you will be disease prone
For most smaller piranha species, you will need a minimum group of 4, and a 4X2X2 foot, 6X2X2 being better, tank. That's 300l, or 450l depending on which you get... They are messy, so you need two big externals (Fluval FX5 or Eheim 2080) and a larger heater or two (Hydor EHT300, preferably X2)