I realize there are numerous related questions on freshness of mussels:
I couldn't find exactly what I'm looking for. So feel free to argue if you think this is a duplicate and I've just missed my answer.
I've bought this: http://canadiancove.com/products/high_oxygen_tray_packs here in Canada numerous times (Costco if anyone is curious, half the price of everywhere else, which is awesome for a landlocked province). The product is usually very good; no bad smell, very clean, responds well when rinsed/tapped lightly etc... I always check to make sure the vacuum seal is good and their "best before" date is as far out as possible. This time, I noticed a higher count of mussels that appear to be dead; at least a third were questionable. There was a noticeable smell that usually isn't there when I opened the pack. The ones that were clearly dead, smelled off, no movement when rinsed/tapped, no spring, etc... Assuming I've done a good job of sorting the dead from the alive, can the dead ones giving off smell, pollute the rest of the batch that I should probably avoid the whole thing?
I tried cooking the ones that were clearly alive and they tasted off anyway so I ended up discarding them. I decided it wasn't worth the risk. Just curious for next time.