very common question but alittle different...

[Otherone]

It's hard enuff to get a compatible new world cichlid mix, throw in a 6" Piranha and your peaceful tank is now a stressed out all you can eat buffet.

Altough I do own a single RBP, I wouldn't recommend it. For a single Piranha I'd go with S.Elongatus or S. Maculatus, odds are they'll be more personable.

 

[ballinouttacntrol]

Here's a thread where the original poster attempted to do the same thing.

http://www.monsterfishkeepers.com/forums/showthread.php?t=288177

Personally, I fear for the worse and think he stopped the experiment but I don't know that for a fact. I based that on the fact that he's still an active member but hasn't returned to the piranha section in 2-3 months. It's always nice to hear from personal experience so maybe you can contact him and ask how it went.