You have just broken the first rule of buying a ray, always check to see if they eat in the store before buying, alway choose a variety of food not just one type of food. You are just using black worms, you can start them off with other food then u can try to get them to eat the food u wnt them to eat but get them to eat first try shrimp, night crawlers (earthworms) , ghost shrimp, tilipia, and trout. There is a website that he tries to get his new motoro to eat shrimp but it turns out he like trout. fillete the trout, cut it, and freeze it. Tillipia is best. There is also a time wen u have to make a mixture for the ray, add, earthworms, blackworms, shrimp, these little small fish i forgot the name starts with a m small feeding ones, and maybe trout fillete, beat it and mush it together using a blender or something and put it in a turkey baster and feed the ray with it try that. Make a little because they dnt always go for it, and also scared of it.