Originally Posted by JohnL
As the others have said, don't try to re-freeze. But if you buy them on day one and shell them for stock, I don't think that you would have a problem if you cooked them the following day. I usually put them in bowl, cover with plastic wrap, put that bowl into a larger bowl filled with ice and then put that bowl into the refridgerator. Your best bet though is to ask your butcher when the shrimp was thawed. The fresher, the better!
That's what I would do.
I also recently started buying frozen American shrimp rather than what the supermarket carries in the case. The taste and texture are great, plus I just leave the bag in the freezer and use what I need. They defrost in no time at all in a bowl full of cold water.