I am thinking about trading in my little cichlids and buying a Black Ghost Knife. it would be with my two 4" bluegill, one 2" bullhead catfish and maybe a pleco. will the BGK be ok in there?
I am way late on this thread but I will still give you my opinion. Black ghosts and very peaceful and secretive fishes that need their own hiding places to call home. The native fishes you described appear to me to be aggressive and rather territorial like a cichlid as they grow. I could be wrong of course, but my advise would be to not add the knife as he could get beaten up with time and killed.
I agree with with the above statement, but I differe in the fact that I feel it will also depend on how large a tank they are in, and also how many caves and hiding places you give them all to chose from
Nothing is an absolute truth in fishkeeping. The combination you want to have could work but, on paper, it doesn't sound like it will. Black Ghost knives are very peaceful and your fishes are rather aggressive so it could spell trouble for the Black Ghost to compete for food, being harrassed, etc.