it doesnt work like thatkeepinfish;4302946; said:they are EVOLVING to live on glass bottom....duh
take a man and throw him in the sea he wont grow fins and swim off but he will try to swim as best he can
with a ray on a glass bottom its just making do with what it has to live put that ray even a captive bred ray in a tank with substrate and it will dig and cover its self in substrate even if it has never seen it before
its like a caged bird that has been born in a cage and never had the chance to fly open the cage and it will fly away because thats what comes natural to it FACT