The taste and texture of deep-fried foods can sometimes be difficult to preserve during the reheating process. With fried fish, you'll want to capture the crunchy crispiness of the coating and the tenderness of the fish when heating leftovers. There are a few options from which to choose; your decision will be based on your time requirements and how particular you are about preserving the original characteristics of the food.
Take out a dry skillet, and place it on the stove. Turn the heat on to medium, and add a bit of cooking oil. Take your cold fish and place it in the pan, heating it for a few minutes on each side. Flip the fish once or twice to make sure each side is heated and crispy like it was in its original state. Cooking the fish on low heat would lead to sogginess and leave the coating mushy, while using high heat may burn the outside while keeping the centre cold, so find the perfect middle setting if you choose this method.
Preheat your conventional oven to 177 degrees Celsius, and let it achieve maximum heat as you place your leftover fried fish on a flat baking tray. Make sure to coat the surface of the sheet with oil or a portion of non-stick aluminium foil. Once the oven is hot enough, place the fish inside, leaving it to bake for 15 minutes. This should thoroughly heat the fish and crisp up the batter.
If you have a countertop toaster oven, you can reheat your fish using almost the same method as with a conventional oven. Take your fish, wrap it almost fully in tin foil, and sprinkle a few drops of water on top of it to prevent it from over-drying during the heating process. Preheat the toaster oven to 177 degrees Celsius, and place the fish inside on the rack once the oven is hot enough. Check the food frequently to monitor its progress. You want the breading crunchy and the fish moist, so don't leave it inside for too long.
If you don't have enough time to use any method other than a microwave oven, be aware that the steam from the machine may result in soggy, rubbery fish if you're not careful. The best trick is to wrap your fish in a paper towel before placing it in the microwave oven; the paper will absorb much of the moisture and prevent the breaded coating from becoming a mushy mess. Take into account the size of your piece of fish when deciding how long to heat it. Overheating will lead to tough fish.