Green sunfish are mean fish I ever owned, beat up every fish in my tank and ate two of x-large corydoras. IMO I wont get a oscar until I get my 75gal for SURE then add a oscar to that 75gal but even 75gal is too small for fullgrown oscar. I would go for 125gal for house both oscar and green sunfish. But after I read all in thread...catfish, sunnies, oscars...sounds like too many fish you have, gar man.