Sounds good and it will work, but you have no idea how big motoros actually get. I have a 240 ray tank that had fronts in it. The rays are now 12 inches plus in diameter and eating 1/2 pound of food per day. Get a male ray if you can, they stay smaller. A small leopoldi or leo hybrid would be best, because they stay the smallest and are very hardy. The price is high though usually for leo's of any kind.
Even if your alpha is 8 inches, the sub dominants are smaller. I had a few incidents with coming home and finding frontosa heads left from a night time raid of the caves. A big stingray can eat whatever it wants. I am not saying it can't be done, but if there is a fight and the ray is bigger than a juvenille, the fronts will lose.
Also, in the beginning it is hard to get most rays to eat. Out of the bag is a good deal for you, but also a good deal for the shop because if it dies on you then you eat the cost, if it dies on them then they eat the cost.
Rays don't ship well and come in stressed a lot. Read up on them before you consider it.
Last thing, if you go to a shop that presumes it is a male and can't tell you for sure with a ray, go somewhere else. The difference is obvious, claspers are only found on males and are present at birth. If they honestly can't tell then you need to find another shop for your business.
