Vacuum packed fish is an excellent way to purchase fish in the grocery store. Vacuum packaging keeps the fish from drying out by preventing water loss. Vacuum packaging, also called Reduced Oxygen Packaging (ROP) is used because it allows for an extended shelf life in the freezer by reducing off odors and texture changes which may result in spoilage. When food is vacuum packed, air is sucked out of the packaging and then the packaging is hermetically sealed. Fish packaged this way are very popular in grocery stores, it’s important to handle the fish correctly.

What’s the concern? Clostridium botulinum and Listeria monocytogenes are the bacteria of primary concern when thawing vacuum packed fish.

Clostridium botulinum (C. botulinum) is an anaerobic bacteria (meaning they live and grow in low oxygen conditions) that forms spores which allow it to survive in unfavorable conditions. When the right conditions are present, the spore will develop into a vegetative cell which can produce a deadly toxin. The toxin causes a life threatening disease call botulism.

In order to prevent the production of the toxin, Michigan State University Extension advises it is important to keep food such as fish that is vacuum packaged (no oxygen) at the proper temperature. C. botulinum forms toxin more rapidly at higher temperatures than at lower temperatures. As storage increases above 38 degrees Fahrenheit, the time required for toxin formation is significantly shortened. Many home refrigerators have temperatures above 38 degrees Fahrenheit. Additionally, if thawing the fish in cold water, the temperature may also be above 38 degrees Fahrenheit.

 Labeling on frozen fish products in ROP 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.

Listeria monocytogenes is a bacterium that can contaminate food. If present, it can cause a serious illness primarily for high risk individuals such as older adults, pregnant women, newborns and adults with weakened immune systems. Unlike many bacteria, Listeria can grow and multiply in some foods in the refrigerator. Vacuum packed fish is not commercially stable or shelf-stable and must be refrigerated. Even while thawing, it is very important to following thawing guidelines provided by the processor.

Vacuum packaged fish results in a tasty and superior product when it is prepared. It is important to follow thawing recommendations when preparing the product at home.