How to Defrost Fish

Fry haddock

The Spruce / Cara Cormack

Commercially frozen fish is one of the great innovations of the culinary world. In the old days, you could never know for sure if the fish you were buying was truly fresh. Today, most fish and seafood is flash frozen right on the boat within minutes after it's caught, preserving its peak freshness and ensuring that it stays fresh all the way to your kitchen. 

It's even packaged in vacuum sealed portions, for extra convenience. All you need to do is defrost the fish and cook it. So what's the best way to defrost fish?

How to Defrost Fish

The main concern when defrosting frozen fish is food safety. By that we mean minimizing the growth of bacteria that can cause food poisoning. And it turns out that the most efficient way to defrost fish also happens be the safest.

Note that we're assuming your fish has been commercially frozen and is vacuum sealed. This includes individual portions, whether it's steaks or fillets, and even whole fish such as tilapia or trout

There are two preferred methods for thawing frozen fish, and which one you'll use mainly depends on how much time you have. 

Defrosting Fish in the Refrigerator

The absolute best way to defrost fish is to do it in the refrigerator overnight. Just transfer it from the freezer to the fridge before you go to bed and it'll be ready to cook the next day. If your fish is vacuum sealed, you don't have to worry about it leaking. You can just place it on a plate or a tray or even directly on the shelf of the fridge. Then when you're ready to cook, snip open the plastic, rinse the fish and dry it with paper towels, and you're all set. If for some reason your fish isn't sealed, go ahead and seal it in a resealable plastic bag so that it doesn't leak. 

The reason this method is the best is it ensures the fish is never warm enough to give food-borne bacteria a chance to multiply. The main drawback is remembering to do it the night before. If the pieces are thin enough, you might be able to get away with doing it in the morning if you're planning to cook it that night for dinner. 

Defrosting Fish in Cold Water

The next best way, and it's quite a bit quicker, is to defrost your fish in cold water. Again, assuming your fish is sealed in moisture-proof packaging, simply place the fish in a shallow dish in the sink, fill it with water, and leave the faucet running a tiny bit so that a narrow stream of water runs into the dish. And make sure the water is cold, not warm, and definitely not hot.

Because it completely envelops the fish, the cold water will thaw it faster than the cold air of the fridge. And even a tiny stream of water will produce a slight convection effect, which will speed the process significantly. This technique should take no more than 30 minutes, although you can check it in 20 to see how it's going. As before, once it's thawed, snip open the packaging, rinse the fish and dry it with paper towels. 

You can also combine the water method with the refrigerator method. Simply immerse the package in water in a pan and transfer the whole thing to the fridge. This will take a bit longer than the running water method, but still quite a bit quicker than the ordinary refrigerator method. The advantage is that by leaving it in the fridge, you minimize the risk of bacteria.  

But whatever you do, don't submerge fish in water if it isn't sealed in plastic. This will cause it to become waterlogged. If it's not already sealed, seal it in a plastic freezer bag with all the air squeezed out before immersing it. Squeezing out the air is critical to ensure that the cold water is in contact with the fish.

How NOT to Defrost Fish

Between these two methods, there's really no reason to try anything else. But in case you're tempted, remember that thawing in warm water, or on the countertop at room temperature, are both no-nos. Both of these methods can create a food safety hazard. And the warm water can cause unwanted texture changes.

And as for the microwave, this is the worst method of all. The microwave heats unevenly, and will end up cooking parts of the fish while also creating a food safety hazard. Given that you can, in a pinch, use the running water method and thaw your fish in half an hour, there's really no reason to resort to this.

Why Does Frozen Fish Turn Mushy?

One of the issues that can affect frozen fish is that once thawed, it can have a mushy texture. This can happen if you submerge the fish directly in water without plastic around it, as we mentioned earlier. But there's another factor that can cause this, though it's pretty rare. 

Fish, like all living things, is made up of millions of cells, and these cells contain liquid. When fish is frozen, that liquid also freezes. If the freezing process happens too slowly, that liquid can form ice crystals that will rupture the cells of the fish. When that fish is later thawed and cooked, this liquid will leak out, producing a mushy texture. 

Thicker steaks and fillets, because they take marginally longer to freeze, are more likely to exhibit this issue, although if it's been frozen properly, it shouldn't be a problem. But assuming you defrosted it properly, if this does happen, it was most likely caused by something that occurred before you bought the fish, not by the way you thawed it.