I currently have 12 discus from 3 and a half to 6 inches in with my pair of motoros, the boy is 6in. and the girl 7in. and I have never seen any aggression what so ever. The discus eat black worms off there backs, and I had to pull one for pecking at my females eyes. I guess every ray is different, but I have never had any problems. The discus and rays together look stunning as well.