For a long time, I believed this advice: Don't refrigerate your fish sauce. Whatever can happen to this brew has already happened; it's not going to go bad. You can pass your half-empty bottle ...
The sauce was to expire in Nov 2013. I kept it in the fridge all the time. The thing that grew on it was white in color (just like cotton). There was a greenish center. The overall "ball" was about 1 ...