Defrosting Fish in Vacuum Packaging? Here’s Why That’s a Bad Idea

Frozen fish might be one of the most underrated staples in your kitchen. It’s accessible, often more affordable than fresh options, and thanks to modern freezing methods can be incredibly fresh. In fact, many so-called “fresh” filets at the grocery store were actually frozen during transit. But before you toss that salmon or cod into your fridge to thaw, there's one important food safety detail you need to know: you should never defrost fish while it’s still in its vacuum-sealed packaging.

Why is vacuum-sealed packaging risky for defrosting?

Vacuum-sealed packaging is commonly used for frozen fish because it removes oxygen, which helps maintain texture and taste while preventing freezer burn. But when it comes to defrosting, that oxygen-free environment can become a hazard.

The reason? A dangerous bacteria known as Clostridium botulinum. This bacteria produces a toxin that causes botulism, a rare but life-threatening illness that affects the nervous system. According to Alyssa Pilot, a food safety specialist at the Washington State Department of Health, this toxin can grow in low-oxygen, low-temperature environments exactly like the conditions inside a sealed vacuum pack sitting in your fridge.

“Clostridium botulinum spores can grow and produce a toxin which attacks the nervous system,” says Pilot. “A tiny amount of this toxin can cause severe symptoms and is often fatal if not treated immediately.”

Even more alarming? You can’t smell, see, or taste botulism. According to the CDC, early symptoms may include:

• Muscle weakness

• Blurred or double vision

• Difficulty breathing or swallowing

Why fish is especially vulnerable

There are several types of botulism, but frozen fish is specifically at risk due to Type E, a strain often found in aquatic environments. What makes Type E especially tricky is that it can survive and thrive at low temperatures as low as 38°F, according to seafood safety expert Michael Ciaramella from New York Sea Grant at Cornell University.

That’s well within the range of most home refrigerators, which the FDA recommends keeping at 40°F or below. So even if you think your fridge is doing its job, it might not be cold enough to prevent the bacteria from multiplying in vacuum-packed fish that’s left to thaw.

How to safely defrost frozen fish

Here’s the good news avoiding the risk is surprisingly simple. Before placing frozen fish in the fridge to thaw, cut open the vacuum packaging to expose the fish to oxygen.

“The safest way to thaw frozen fish is to remove it from any vacuum packaging and place it in the refrigerator,” says Pilot. This helps ensure the bacteria doesn’t have the conditions it needs to grow and produce toxins.

Other best practices:

• Keep your refrigerator at 41°F or colder

• Place thawing fish in a container or on a plate to catch any juices

• Cook thawed fish within 1 to 2 days for best safety and quality

Can you defrost fish in water?

Yes cold water thawing is also a safe method as long as you remove the fish from its vacuum-sealed pouch first. Place the fish in a resealable bag, submerge it in cold water, and change the water every 30 minutes until thawed.

Does this apply to other vacuum-sealed foods?

Not necessarily. According to food safety guidelines, the botulism risk is unique to fish, particularly due to the presence of Type E spores. Other vacuum-sealed proteins, like chicken or beef, aren’t considered high risk in this regard when stored and cooked properly.

That said, always check the packaging instructions for guidance. If it says “keep frozen until use,” there’s likely a reason.

Final takeaway

Frozen fish is a healthy, practical addition to your weekly meal plan but food safety matters. Never defrost fish in vacuum-sealed packaging, and always take a moment to review thawing instructions. A small step can make a big difference for your health.

Looking for more tips like this? Subscribe to our newsletter for expert-backed advice delivered weekly.