i dont have a ray but i went swimming with them one time and when we gave them food they wouldnt bite u they would just suck it up realy fast and hard. sometimes they wuldnt let go for awhile though hope this helps
Use a feeder stick. There could be bacteria, etc on your hands, even if you have washed them. Also this will lead to your ray always associating your hand with food, which could cause some problems while cleaning the tank. Bo