Nothing can be kept with piranhas long term, anything will eventually get eaten. It may last for an hour, it may last for a few months, but eventually you can kiss it goodbye.
well i have heard that large rbp's tend to leave smaller fish alone like neon tetras. so maybe if its very small and they are very large.
sry not much help. i dont keep my piranhas with anything. except the occasinoal rosy and he goes byebye in five seconds sooo....
and some advice dont try banjo cats i believes the are toxic if i m not mistaken. sooo...maybe a small raphael or something armored with lots of hiding spot but u might not see it at all.
I've kept a pleco with mine for months, they were generally scared of it. But I've read that eventually they figure out to flip them over and eat the belly. I moved mine. I'd say don't bother wasting a catfish. P's are pretty unpredictable and it would probably become dinner.
i have kept a pleco with my p's for several months (6ish i think) and they don't even notice him or care less when he swims around, but it is always a experiment when mixing with piranhas but i found the trick is to just keep them well fed and u won't (shoudn't) have any issues...knock on wood