really well... i've had this mbu since he was really really small.... he has never hurt a fly.... now i'm really sad for the main tank where he is, is gonna have 5 asian aro's and 2 ray couples next week, so i'm tanking him out to another tank... i think it whould probably be best not to risc it.... i know he wont bother the aro's hes always lived with aro's, but i'm not so sure with the rays... it's sad because it's one of my favorite fish, but... probably best, don't you think?