I dont keep rays at the moment but have been doing lots of research and most places say its not a good idea to keep birchers with rays. As the bircher cant see too well it sometimes just lunges at things it sees moving and to see what it is uses its mouth which if its a rays disc that its investigating could have really bad consequences as the wound could get infected. Also if the ray is afraid that the bircher will attack it etc this can cause 'acute stress' then means that you most likely wont notice anything but the ray will have to be always alert so have no resting time. This has a number of problems; it could slow down growth rate, reduce chance of breeding, reduce the apparite of the ray and generally the ray wont feel safe in its enviroment.