Today for the first time I noticed bite marks on one of my female motoro rays. One bite actually left a gap in her disk. In the tank (300 gal) are 4 rays, 3 female and 1 male. The male is not mature and I would guess will not be mature anytime soon (8" disk) while the female are all larger. They are fed about 3/4 lb. of a mix a fish, shrimp, and pellets each day. Who do you think is the aggressor and what can I do to stop it?