Fish get along well. Some fish do avoid other fish (e.g., all big fish avoid the Trimac, but all little fish don't pay him any mind; most little fish avoid the Jag, but big fish swim right next to Jag without even noticing him). Occasionally but rarely see a gill flare. Never any lip locking. There is so much drift wood to dart in and out of that it's impossible for there even to be any chasing.
Of course, all of the fish are of equal nastiness and aggressiveness, so it works. Throw a slow moving 12" Oscar in there and he would probably be toast. GBG