You're showing responsibility here unlike most people who would buy fish on impulse. Unfortunately, there is not a single piranha except ones often unavailable with size no more than six inches that will fit in your tank permanently otherwise it could serve as a good quarantine or rearing purpose if you do plan to upgrade your tank to as big as 180g.alrighty thanks ill take a look at your link but i was thinking permanent but i make shur to do research be4 buying anything