my 16" marbled motoro has lost interest in food and I have noticed he is loosing his fat tail. I don't want to say it, but i think I can start to see his pelvic bones. He has been in this tank for two years and i haven't introduced any new fish in 6 months and never feed live food. Water quality is perfect. I have had some recent problem with one of my fish killing others in the tank just not sure which fish is doing the killing. It could be stress but no one ever messes with the ray. Any suggestions would be appreciated on how to get him to accept food.