Ive got a lm about 10", and I keep it w/ an 8" smallmouth and a 4" bluegill. The lm tends to pick on the sm alittle (mostly just chasing, its never left a mark on it) and everything leaves the bluegill alone, and the bluegill leaves them alone. I also have about a 6" channel cat in there that also gets left alone. When my bass were about 6" they both ate 4" chubs that WERE tankmates for awhile lol
