How To Tell If Frozen Fish Is Bad? (5 Signs of Spoilage)

Perhaps you bought frozen fish at your local supermarket, or maybe you caught some deliciously fresh fish and decided to freeze it for later. Whatever it is your case, odds are you have some seafood frozen in a remote corner of your freezer, waiting to be thawed and cooked.

But you may grow wary if it has been more than a few days. How can you even tell if frozen fish has gone bad? Can frozen fish spoil, even if safely stored at below zero?

Although frozen fish can go bad under certain circumstances, there are some nuances you need to know first. Factors such as the freshness of the fish, temperature, thawing process, and even the type of fish can affect the quality of your meal. 

Curious? Worry not. Let’s take a look at how to tell if frozen fish is bad, signs of clear spoilage, and the secret for long-lasting storage.

5 Signs That Your Frozen Fish Has Gone Bad

frozen fish smells fishy

Ideally, frozen fish has been sealed and stored in the freezer while still fresh, which means that it should retain the same quality signs. If stored properly, upon thawing, the fish should be almost as good as if fresh.

So, it’s most important to trust your senses beyond checking for Use-by dates around your frozen fish package. Your eyes, nose, and hands will tell you all you need to know about your fish, so make sure to look for the signs of spoilage carefully. 

1. Slimy Texture

With time, fish ages and slowly start to decompose, which can cause the outer surface to degrade and turn slimy and slightly gooey. This can happen even to frozen fish, particularly if it wasn’t stored fresh or if it has been in the freezer for far too long.

However, remember that sometimes, thawing fish can cause the moisture on the fish’s surface to come across as slightly slimy. Make sure to check for other signs before assuming it is spoiled.

2. Pungent Smell

Fish smells like fish but the scent should always be mild and fresh—reminiscent of the sea. You should immediately suspect spoilage if the scent turns sour, acidic, pungent, and ammonia-like [1].

A strong fishy smell reminiscent of rotten eggs is a clear sign that decomposition has begun to take place. Fish that has been frozen solid may not immediately emit any scent, so you should be careful during the thawing process.

3. Discoloration

If you have frozen fish fillets, inspect the color carefully. Whether it is white or pink, it should be a uniform shade—remain suspicious of any discoloration, darkening, or off-color patches. 

This inconsistent coloration may be a sign that the fish had begun to rot by the time it froze or developed freeze burn due to exposure or extended unsafe refrigeration.

4. Presence of Ice Crystals

If your fish has developed crystals inside the packaging, they can mean that at one point, the product’s cold chain has been broken—the temperature thawed and then refroze. 

This is particularly dangerous, as the fish potentially reached high enough temperatures to allow bacterial growth, which means that you risk food poisoning. Freezing or refreezing food does not kill the harmful bacteria in your fish and bacteria be revived as food defrosts [2].

However, ice crystals don’t always mean that food was partially thawed and then frozen again; they can also signal freezer burn, but that is hardly better news.

5. Loss of Weight

If the fish feels lighter than when it went into the freezer, it is a sign of deterioration. Prolonged storage in the freezer can lead to loss of moisture, causing the signs of freezer burn, that is, the ice crystals evaporating from the surface of the fish. And gradually, the excessive moister loss will inevitably destroy the texture of the fish. That is why it is critical to wrap the food airtight before freezing.

Is Freezer-Burned Fish Safe To Eat?

freezer burn fish

Yes. According to the United States Department of Agriculture (USDA), freezer burn does not make food unsafe and does not cause illness if consumed [3].

However, it can drastically alter your fish’s appearance, flavor, and quality. For example, fish that has been exposed to freezer burns can be flavorless, dry, unappetizing, or have an off-color. As such, it may be best to discard frozen fish that displays these characteristics.

How Long Does Frozen Fish Last In The Freezer?

frozen fish product

If you purchased frozen fish, going by the “Used By” date can be a good indicator of how long your fish will remain in peak quality. However, it is not an absolute rule—manufacturers merely provide an educated guess of how long they believe the fish will stay at its best [4].

According to the USDA, perfectly frozen fish will remain safe indefinitely, yet it will continue to lose flavor and texture as time goes by. Subsequently, your best bet is to consume frozen raw fish between 3 to 8 months after freezing [5]. 

However, different fish have different shelf life according to their characteristics. In particular, there is a difference between lean and fatty fish since the latter has more fat content and therefore is prone to deteriorating faster. 

Famed website Eat By Date estimates that most types of fish can last in the freezer from six to nine months except smoked salmon, herring, or Albacore tuna which lasts from three to six months [6]. 

How Do You Store Frozen Fish Correctly?

storing fish in freezer

If you purchase frozen fish from the store, your task is to make sure it doesn’t thaw before you can store it in your freezer. Likewise, make sure the package is not open, ripped, or damaged in any way. 

If you’re freezing fresh fish, make sure to do it as soon as possible to prevent bacterial growth. Wrap the fish tightly in aluminum foil, plastic wrap, a freezer bag, or a freezer-safe airtight container to prolong storage time and protect it from temperature shifts until you’re ready to cook it. The most effective way to avoid freezer burns is to vacuum-sealed the fish before freezing [1]. 

For such purposes, the U.S. Food & Drug Administration (FDA) recommends freezing food below 0°F (-18°C), as it is the perfect temperature to prevent bacteria from growing and, subsequently, prevent food decomposition [7]. 

Top Tip: According to the U.S. Food & Drug Administration (FDA), the ideal temperature for storing frozen fish is t or below -4°F (-15°C). If the temperature fluctuates, it can cause the fish to thaw and refreeze, which can lead to a loss of quality and flavor. To ensure consistent temperature, it is best to store the fish towards the back of the freezer, where it is less likely to be affected by door openings and changes in room temperature [7].

How To You Safely Defrost Fish?

defrosting frozen fish

According to the U.S. Food & Drug Administration, there are three ways to thaw frozen fish safely [1].

This first thawing method is widely considered the best for flavor and safety—thaw it gradually by letting it rest in the top part of the refrigerator overnight. With this method, your fish never gets warm enough to become a hotspot for bacteria to grow, guaranteeing it will remain safe by the time you cook. 

Secondly, if you’re pressed for time and require faster results, you have two additional options. First, seal the fish in a plastic bag and submerge it in a cold water bath using a large bowl or a kitchen sink. Replace the water every 10 to 15 minutes, ensuring it stays below 40°F (4.°C).

However, you may also defrost it in the microwave using the defrost setting until most of the ice has melted away. It will take about 3-5 minutes to fully defrost fish in the microwave.

Keep in mind that any of these options are fine, but you must never thaw frozen fish at room temperature or under hot or warm water. 

Read Also: What To Do With Food When Defrosting Freezer? (6 Ways To Keep It Safe).

In Conclusion

If you notice any of the signs mentioned in this article, it is best to discard your frozen fish. Although it can be difficult to waste food, it is better to be safe than sorry. Make sure to store your frozen fish vacuum-packed if possible and keep the temperature 0°F (-18°C) without any major fluctuation.


About Jen Evansy

Nutritionist, researcher, avid home cook, and writer interested in everything nutrition and food-related. Striving to inform, encourage, and inspire all the readers to make healthy and informed choices when it comes to cooking, food, diet, and nutrition.