They live in the same environment and both Pacus and Silver Dollars try to blend in while younger eventually becoming food.Cyclop3000 said:Maybe if tank large enough, same size fish and very well fed...maybe for a while. The piranha will eat fins out of the pacu, especially at a younger age. Personally I would not risk a pacu with a bunch of piranhas, they would eventually try a bite and then you can watch the feeding frenzy.
In the wild these species mix together for mutual advantages, but in a tank everything is different...