Have you tried bloodworms or blackworms? I find that a ray that will reject most everything else will accept one of those options. Another factor could be that it's stressed from its tank mates, especially if it is a wild caught ray. It could also be likely that it hasn't been treated for parasites if it's wild caught.
Hey forgot to update, ray was just stressed from shipping, he ate like a champ tonight, would probably even eat more if I wanted to put more food in. (Earth worms, shrimp, cut Tilapia) he wasn't picky.