I'm guessing that seafood displayed in refrigerators aren't exposed to room temperature
would be fresher than seafood exposed on ice?
Based on your other post, I am assuming you are in Canada. And in Canada, fish have to be labeled previously frozen or fresh based on its storage history. So assuming we are only talking about the ones labeled fresh. Here is what I have experienced.
Between choices above the "fresher" option doesn't really exist both options the fish have been sitting for some time. As a result that "shore-side" freshness is lost. However, a more optimal tasting fish would be from the covered ones because it is chilled and has not exposed to room temperature air for as long. This helps preserve the moisture and texture of the fish.
The other thing to consider is, were the fish (or other seafood) farmed or naturally caught. Because, and this is especially true for fish, the taste will differ greatly, as will even the colour of the meat.
So in short - the covered one is more "fresh" and neither is truly fresh.
Hope this helps.