Live raw Mussels will keep in the fridge for up to 2 days before they go bad.
Be sure to cook the live raw Mussels within 2 days or discard them after that.
When storing live raw Mussels in the refrigerator make sure you store the Mussels in an open container and cover the Mussels with damp cloths or paper towels.
Do not put the live raw mussels in sealed containers as that will kill them and make them unsafe to eat.
Raw Mussels must be kept alive until you cook them otherwise they are no longer safe to eat even when you cook them.
So you must make sure the Mussels are alive when you're getting ready to cook them.
Use the live Raw Mussels within 2 days because after 2 days the mussels will usually die even in the refrigerator.