But keep in mind that thawing and refreezing any food will take a toll on its quality. In the case of your fish fillets, you’ll likely see some changes in texture and taste after the second thaw. So you might want to opt for using the fillets in a chowder, stew or casserole, where the fish can be of less-than-perfect quality.
Refreezing is not an option, though, if the fish wasn’t thawed in the refrigerator to begin with.
If you thawed the fillets in the microwave or in cold water, you should cook them immediately before freezing, says the USDA. That’s because with either method, the fish fillets could have at least temporarily warmed up to a temperature higher than 40°F. At that point, harmful bacteria can begin to multiply and only further cooking will destroy it; simply refreezing the fish fillets won’t do the trick.
Finally, if you thawed the fish fillets on the counter or in hot water, you shouldn’t eat them at all. The USDA cautions that it’s dangerous to eat any fish that’s been thawed under those two methods, as the outer layer of the food would have been allowed to sit between the bacteria-breeding temperatures of 40° F and 140° F for far too long to be safe.