The optimal way of defrosting frozen fish is to let the fish thaw in the refrigerator, which preserves the meat's structure. This can take hours, however, and is not always feasible if you have fish that must be cooked soon. Defrosting frozen fish in the microwave is a delicate process that requires careful monitoring, otherwise, you risk cooking the fillet unevenly and creating pockets of mushy or tough meat. Changing the fillet's position in the microwave often will help it defrost evenly.
Place the fish in a single layer in a microwave safe container.
Place the container in the microwave. Set the microwave to 50 percent power and set the timer for five minutes. Press start on the microwave, flipping the fish every two minutes.
Check fish for frozen areas after five minutes. Knock off any chunks of ice clinging to the fish using a fork, and separate any pieces that are still frozen together. Place the fish in the microwave for up to four more minutes if there are still frozen areas.
Add any spices or vegetables to the container of fish. Cover with a sheet of plastic wrap and poke a few small holes in the top using a fork to allow a vent for steam. Microwave on high for six minutes to cook the fish thoroughly. Cook for an additional three minutes if the fish does not easily flake.