When I cook live clams, I usually purchase them from the local grocery store on the day I plan to prepare them. However, sometimes that is inconvenient for me to run to the store the same day.
So my question is how far in advance can I purchase them and keep them in refrigerator until I am ready to cook and have them still safe to eat?
The previously linked duplicate doesn't truly answer the question I asked, although I do see it is related. The question states that the clams in question were left out in cold water (not in the fridge). and the answer just mentions that they are "exceedingly perishable" and that they shouldn't be eaten if they died before cooking. It doesn't give an idea of what length of time that can be kept refrigerated.
Best Answer
Unlike almost any other food item, you can recognize exactly when a clam is no longer safe to cook: when it's dead. So, there are no storage time rules based on time periods. If it's alive, you cook it - if it's dead, it's unsafe.
As for an estimate of how long you can keep them until they die - it doesn't have a precise answer. You can buy them the day before, and with good storage, most of the time, most of the clams will still live on the next day.
The longer you try to keep them, the larger a proportion of the clams will die - but there is no strict number of "you can keep them for X days". I'm not aware of a precise function in the sense of "if you keep them for X days, you have to expect Y% loss" either. So, experience has shown that it's best practice to buy them the same day. If you prefer to buy them earlier, you can do this, you're simply taking a chance that you'll end up with less clams (or no clams) and nobody can tell you how much less.