Mbu is in a tank on its own due to it eating half of a p.congicus and biting the head of my arowana. Your all talking like my tank has changed massivly I havent had rays in this tank for quiet some time the only fish to of gone is the Arowana. Thats it and I have added a school of 10 clown loach which ina big group in a big tank are not as you call the bellybutton fish. I still have all my tigers, my royal knife my pearsei, I have just added a few more not as aggressive fish and will be finishing it off with a group of 6 Hoplarchus psittacus which I will let CFC fill you in on how these are not "bellybutton fish".