In my opinion, the best tank mates for rays are more rays...but I know guys who keep severums with rays w/o much trouble. You can post singray threads in the bottom dwellers forum...there's a sub-forum just for rays, that's where you'll usually find me! Also, you'll need to start planning for a much larger tank, motoro stingrays get huge. 20+ inches for males, 30+ for females. 8 feet by 4 feet minimum tank size