Michigan State University Extension (MSUE) scientists on May 31 published an article urging consumers and foodservice employees to "open your vacuum packed fish before thawing." The reason? Both Clostridium botulinum and Listeria monocytogenes can survive in reduced oxygen packaging at refrigerator temperatures, and thawing the fish before opening the package may promote the growth of those pathogens, according to the article.
The article provides additional information on both types of bacteria and the illnesses they can cause. It especially focuses on Clostridium botulinum, explaining that the anaerobic bacteria form spores which, under favorable conditions, develop into vegetative cells that can produce the toxin that causes botulism.
"In order to prevent the production of the toxin, Michigan State University Extension advises it is important to keep fish that is vacuum packaged at the proper temperature," the article states. It explains that as storage increases above 38º F, the time required for Clostridium botulinum to form toxins decreases significantly. Thawing fish in the refrigerator or in cold water may allow the fish's temperature to rise above 38º F.
Further, the article points out, "Labeling on frozen fish products in reduced-oxygen packaging will state: 'The fish should be kept frozen until time of use and prior to the fish being thawed under refrigeration or prior to or immediately upon completion of thawing, the fish should be removed from the packaging.' By opening the packaging when thawing the vacuum packaged fish, oxygen is present and the spores will not produce the vegetative cells that produce the toxin."