Most fish you find in the store has been frozen at one point of another. Freezing helps lock in nutrients and transport it safely.
What if you bought frozen fish, thawed it, and didn’t have time to cook? Or what if you baked a big batch of salmon and have way too many leftovers?
Can you refreeze fish? According to the USDA Food Safety and Inspection Service, the answer is yes, though quality may not be on your side.
Fish Safety
There are all kinds of harmful bacteria that can contaminate fish. Salmonella and other nasty microbes can make you sick if you don’t handle fish properly.
Though eating raw fish is popular in many cooking styles, the FDA recommends cooking fish to 145ºF to kill harmful bacteria. If you want to eat raw or partially cooked fish, eat at your own risk. Additionally, if you notice the fish smells sour or overly fishy, it’s not safe to eat.
Safe Freezing
When freezing fish, first make sure it’s securely wrapped—use an airtight bag or extra layer of plastic wrap for good measure. If you buy fish from you local fishmonger, you definitely need to re-wrap it.
Then make sure your freezer hits 0ºF or below so it freezes quickly and stays that way for as long as you need. It also doesn’t hurt to put a date on the package, just in case it gets lost in the freezer.
Safe Thawing
The safest way to thaw fish is to do it slowly in the fridge overnight. But if you’re running short on time, place it in a secure ziplock bag and set it into a cold water bath. Make sure to change the water every half hour so it stays cold.
You can also thaw fish in the microwave if absolutely necessary. Use the defrost setting and turn off the microwave when the fish is soft but still icy. Just make sure you cook it immediately after thawing, as some parts may start to cook.
Refreezing Uncooked, Previously-Frozen Fish
Didn’t have time to cook all the fish you thawed in the fridge? It’s safe to refreeze thawed fish if you do it within 2 days. However, when it’s time to unthaw again and cook dinner, you may find that certain pieces are a dryer than usual, as moisture is lost each time you thaw out the fish.
Many people prefer not to refreeze fish for this reason, as the flesh is also more delicate than meat. Regardless, make sure you thaw properly to maintain food safety.

Refreezing Cooked Fish
After baking too many salmon filets, you’ll need to refreeze the leftovers.
Be sure to freeze them within 3-4 days, and don’t refreeze anything that’s been left out on the counter and out of the fridge for longer than 2 hours.
However, if you grill fish outside in the 90º heat, it’s best to refreeze it within the hour.
Again, most people don’t recommend refreezing cooked fish, simply because you can loose those delicious flavors and textures.
As far as safety goes, you’re okay to freeze your leftovers when dealing with flounder, tuna, salmon, cod, halibut, swordfish, catfish, and many other popular dinners.
Sources:
National Advisory Committee on Microbiological Criteria For Foods. (2008). Response to the Questions Posed by the Food and Drug Administration and the National Marine Fisheries Service Regarding Determination of Cooking Parameters for Safe Seafood for Consumers. Journal of Food Protection, 71(6), 1287-1308. Retrieved November 18, 2018, from https://www.fsis.usda.gov/wps/wcm/connect/de34121e-cdaf-4d2a-9f9d-1976926e1715/NACMCF_JFP_Manuscript_07-612R.pdf?MOD=AJPERES.
Food and Drug Administration. (2018, November 15). Fresh and Frozen Seafood: Selecting and Serving It Safely. Retrieved November 18, 2018, from https://www.fda.gov/food/resourcesforyou/consumers/ucm077331.htm
USDA Food Safety and Inspection Service. (2013, June 15). Freezing and Food Safety. Retrieved November 14, 2018, from https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/freezing-and-food-safety/CT_Index
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