I used to have two pairs of Motoro in a 90 gallon in my old pet store until my brother took them home and they had a mishap. Motoro's I find are the easiest to keep of the two species I have had experience with. They are the easiest to wean off of live food. Most F/W rays are wild caught though I know a few people that have started breeding them. I have one Motoro in a 90 that I just setup today. rays have voracious appetites and will eat any small fish they can get in their mouths. I feed mine a combination of foods when they are small including krill, pieces of shrimp (tail on at first), blood worms , live ghost shrimp, feeder guppies, earthworms and later goldfish. Having said this water parameters need to be perfect Rays are intolerant of nitrates and ammonia. If you want ease of keeping go barebottom for two reasons
1) you are less likely to damage the rays disc
2) Its easy to keep clean after your messy eaters finish
heaters need to be covered or put in the sump as rays easyily burn their discs leaning against it. Keep your water temperature 78 degrees or warmer. Rays are very sensitive to medicines even those that say SAFE FOR SCALELESS FISH. Large water changes are a weekly constant and I run carbon continuously in my ray tank. They are fascinating creatures and can be taught to feed from your hand. Though I warn you I was cleaning my tank once in the store and got distracted it was a very painful andslightly debilitating experience. My left arm was throbbing and then nub for several hours so be cautious.