i started off with small datnoids with small bichirs. ive kept almost every bichir. and the least aggressive bichirs were senegals and delhezi's ive had most trouble with the endlicheri;s. swallowing most of my fishes. and also i dont know where he gets "NEVER GET 2 DATNOIDS. Get at least 3, ideally 5+. Or 1." ive kept bichirs for more the 6 yrs never had a problem with pairs or odds. as long as you put in work to care for these fishes you wont have a problem. unless it gets eaten. as for the rays. i would suggest you to get big datnoids if your gonna keep it with rays. 4-5" datnoid should be fine depend on how big of a ray your going to get make sure it is big enough so the ray cant swallow (yikes that didnt sound right -.-) sorry admin. well Good Luck and Have Fun.