If your refrigerator is below 38 degrees F. and you only thaw it you should be ok.  The reason they want you to open the package is to let in some oxygen.  The strain of  Clostridium botulinum that can be present in seafood can produce botulism toxin at refrigerator temperatures above 38 degrees if in an anaerobic condition.   The reason they recommend opening the vaccum seal is to allow oxygen into the package so botulism toxin won't form.  

Hope that helps

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Nellie Oehler