That tank isn't really a recomended size for any ray. Your dimentinos should read a large surface area and depth isn't necissarily an issue. However when you add more water like any fish the amount of waste produced is spread through a larger volume of water in a bigger tank. And rays kidneys produce a lot of waste so be prepaired. As for stunting their growth... Would anyone get mad if I started selling cats that only got the size of a litter box?