Pictus, Raphael, Synos, all work... you could also look at hoplo and some corys depending on what size the firemouth is now, start them together small enough, and its usually ok when they are raised together... I had an Oscar raised with a GT and a cory, within a few months he could have eatten them both, and never touched them until i moved the oscar out about six months later, I still think they would have been fine had I left them all together.