Yes, purveyors often freeze the fish before it is sold. In doing this, any chance of harmful bacteria or microorganisms is destroyed in the freezing process. However, freezing does slightly weaken the flavor and texture of the fish. If you want to be extra- careful when preparing this dish at home, freezing the fish beforehand can be done. However, I have never done this. I always buy my fish from a reputable source and want to preserve the full flavor of the fish.