What should be my staple?

So I live in the east coast and fall is coming. Meaning seafood tends to become more expensive and i need to stock up. What is a good staple i should be feeding my motoro Rays? I have pellets but they dont touch them so i tend to put them in silversides and w.e i can stuff them in. But As a novice stingray owner, what is a good cheap staple? I am currently more worried about their weight management rather than their overall nutrional health right now... do anyone have any suggestions on what i can use as a staple? My rays seem to have trouble with Frozen Market shrimp. they chew it but they spit it out afterwards, i believe it is too tough for them.

I go fishing alot so i have alot of bluefish fillets that i probably wont eat. is it alright i feed them the bluefish fillets as well?

shes doing good, she is still the only truely pellet trained. but she still prefers the frozen food. I was wondering what is your filtration like?

I bought some krill from shark aquarium. never buying from them again... Not shark's fault but the brand they carry is just horrible... it is messy, clouds the water, and falls apart. As for the Shrimp or silversides, do you have a specific place you go to buy that? i have still a ton of frozen shrimp from god knows when my parents bought it.. says exp date was '08 lol... but its never been taken out of the freezer so im going to assume Its still ok for the rays... especially since they are still alive after all this time. it could explain the toughness though. But what about the silversides? is there somewhere i can buy in bulk?