I've kept big O's with big sevs and JD's with no problems. Right now my O is around 10" and he's in with an uaru who's pushing 8" and a bunch of little 2-3" cons. He doesn't bother the cons at all, he occasionally chases the uaru but doesn't bite her or anything...but he hates catfish. I've tried adding a few kinds and he tries to eat them, doesn't actually swallow them for the spines but he bites at them and I find them dead
If you do decide to go with something like a con or JD I'd make sure the O is a bit bigger than they are...
If you do decide to go with something like a con or JD I'd make sure the O is a bit bigger than they are...