It's tough to determine why your motoro isn't eating with the information that you've provided. Here are some questions that need to be answered:
1) How long have you had this ray? If it's a recent acquisition, the acclimation period could last 2 weeks. I had newly imported flower rays not eat for months before something clicked and they started eating everything in sight.
2) What are your water parameters (Temperature, pH, ammonia/nitrates/nitrite levels, etc.) and are the levels pretty constant? This can be a big factor in the ray's comfort level. Drastic fluctuations in water parameters is a killer. Also, raising the temperature to 85 or more may stress the ray more, as well as, raise its metabolic rate and causing it to waste away faster, so be careful.
3) What are you keeping in the tank with it? This is another factor in the comfort level.
4) Is it breathing heavily? If so, there is a product called binox by Jungle Labs that consists of salt and nitrofurazone that helps the ray breathe and to settle down/acclimate better. It turns the water yellow during use, but carbon will clean that up when use is discontinued.
5) Is there a substrate in the tank. If so, there may be a good amount of decaying matter in the substrate that could be affecting your water parameters.
The most successful situation that I've used to induce a ray to feed is feeding live blackworms on a bare-bottomed tank. This way you can watch the ray from underneath and monitor how much food is left in the tank. With a substrate, the worms will bury themselves and become inaccessable. Keep the lights out for the most part. You can always use a flashlight underneath to see if it's eating. The biggest thing is to exercise patience. Constantly throwing different foods, lighting, and messing with it is not going to speed up the process. One thing that many people are guilty of is killing fish with too much care. Everyone means well, but sometimes being too kind is too much.
