I'm not sure if it's always the case, but I'd definitely consider my firemouth a more aggressive fish
I have 4 firemouths with 1 severum in a 55G. The Severum is not fully grown but he is a monster. He really defines his territory which is just about anywhere he is. I tried to keep 3 Severums together about 2 1/2 inch in size but they just killed each other (really tore their fins up). Had to revert to 1. And the one I have was the one being beaten up by the other 2 severums. Hmmm bullied and now he's a bully. I bet there's probably a fish shrink out there somewhere.
The Firemouths are very aggressive but 99% of the time its just with themselves and not the tank mates. Never kept a single firemouth so they could be aggressive on there own.
I had never seen a fully grown Severum before but I just seen 1 and I think I will have to bring mine back to the LFS
because the wife has'nt come around to a 180g tank
So I'm not gonna let him get so big I can't bring him back. Wow the Severum was huge no way is a 55g big enough for him to swim IMO
. This Severum was only 2 years old. Bet he would give ya a good nip!