My GT is the smallest cichlid (4" ) in my 180g, housed with various Vieja, and an Escondido. He's not overly aggressive but he willingly instigates fights with fish 2.5x his size and refuses to back down (just flaring and some minor lip locking). Doesn't do any damage, but fairly territorial. A long time ago I had a fairly large male GT that was a mean SOB. Definitely not going to see the type of aggression that an Amph or Parachromis will bring to the table, but they can hold their own with most CA and SA.