okay, never feed live blood worms as they BITE, literally. They will bite and trust me, it hurts alot, i use them for fishing and have been bitten quite a few times already. As said before, chop earthworms into peices and feed that. If you've only gotten them a week ago, chances are, they 're still getting used to their surroundings. As long as they're eating, then it SHOULD be fine. Did you quarentined them? Are you sure they dont have parasites and such? When i got my first retic it was kinda like how yours is right now, kills ghost shrimp but doesn't eat them, and only eats a little. But after about 2 weeks, they wouldn't stop eating, and the third week, they were already on pellets and market prawns. Chances are, your rays are still adapting to their new tank. O and BTW 55 gallons wont last them very long.