Assuming all of the fish reach their projected max length, would a BGK eat corie catfish or firemouth cichlids? They would be living in a 125 gallon, well planted, amazon biotope tank.
should be fine, but the bgk once large could kill those fish...i have mixed them all...my 13" bgk has killed a 4" aro and killed a few other fish aswell in simmilar size ranges...
Your firemouths will definitely be fine (assuming they are decent size) but I can't say the same for your cories. As long as they aren't one of the smaller varieties you should be ok.