I am only asking this question for the simple fact i have heard quite a bit of you say a red bellied pacu will out grow the tank there in now i dont want to disagree for i have never had them but i am lost considering my son's babysitter has a 55 gallon with a bunch of fish in it and one of the fish is a red bellied pacu she has had the majority of these fish anywhere between 15 and 20 yrs the silver dollar being the oldest anyway her pacu is smaller then the silver dollar and does not appear to be getting any bigger so is there different species of red bellied pacu's or no because hers is still alive and it does not look like it is gonna out grow the tank. oh yeah here are my pronunciation marks forgot em lol . . . . ,, ??????