Young ray, 3 times a day, 1-2 year old ray, twice a day, 2+ year day you can probably get away with once a day. Rays will be hungry being fed once a day, but they can still live off it if the feedings are big enough, their growth rate just wont be very fast. You have to ask yourself how much you are willing to spend on food and if you feel you have the time in your life to feed them twice vs. once. Cant say my rays get fed twice every day (I work 2 jobs and am in school) but I feel guilty when they don't. I wouldn't miss a feeding for my black lab, rays get just as hungry and understand schedule just as well I THINK. You also have to ask yourself if you want them to breed, because if you do I hear that twice a day is a must. Pregnant female = at least twice a day no question, or else baby may get absorbed. Can your filter keep up with twice a day large feedings? Don't necessarily want to sacrifice water quality do you?
In sum: can do once a day for your average ray keeper, but if you want prime tip top shape rays for breeding, feed twice a day.
In sum: can do once a day for your average ray keeper, but if you want prime tip top shape rays for breeding, feed twice a day.