Nothing, nothing at all. I learned the hard way. Going out tmrw to get my pretty girl a bigger tank, all to herself. If you look up my old threads, my 6 to 8" FH beat up, literally took chunks out of my then 25" plus catfish. took chunks out of the fins of my 13-15" algea eater...so on....this is all in a 265g, so there was plenty of swimming room for them. I even tried darter fish for her to play with, to distract her aggression from my beloved catfish. Those "distractors" have become a permenant fixture now, with the exception when I forget to feed the catfish...
I also had her housed with my old oscar, who the oscar was almost double the FH size. Needles to say, my oscar was in ICU for several weeks, with the insides hanging out, literally. She did survive
Had her with many bottom feeders...clown loaches, pictus catfish, three beacon pleco, big whiptails, etc etc
I remember exactly how long the FH and big catfish lived together, probably for a year. I brought them home together. Until one night something just clicked in her. She wanted the tank by herself. Would not except anything more
SHe's very tame and personable with me though, and hand feeds. No problem there. THat's why I can't let her go, and her beauty...
Good luck. Maybe try a niger catfish or ripsaw catfish, maybe an adonis pleco....something more aggressive, but won't threaten the FH
