In the fridge, prik nam pla will not spoil for a long time, however, the flavours will not be as good as fresh. Any leftovers will be fine for 2-3 days, but after that, even though you can still eat it, it won't taste as good. However, if you're making prik nam pla with very little or no lime juice, it will last much longer because it's the fresh lime juice flavour that deteriorates.