This thread really shouldn't be encouraged, guys...piranhas are illiegal in Cali. I suggest you check with your local DNR to see if that applies to Wimples or not. Otherwise I don't feel that it is in the best interest to the keeping of piranhas as a hobby, or actually keeping an illegal animal. What happens if you get caught? You get fined, and who knows if they terminate the animal, or just send it to the nearest aquarium. How is that fair to the piranha?
Besides, piranhas aren't that agressive 99% of the time. I you want a guarenteed mean & bad @ss fish, you're on the wrong board.
I know cichlids are extremely aggressive, I've never had Oscars but I hear they're pretty aggro too! Consider them instead of breaking the law.