When warming previously cooked fish, remember to reheat it slow and low to avoid overcooking. Try the heating methods explained by livestrong.com below to strike a good balance between temperature and moisture. To keep your cooked fish moist while reheating, add a bit of butter over unbreaded fish or a few drops of water to the bottom of the dish used to reheat the fish. If you are a fan of foil, you can cover unbreaded fish loosely to retain the moisture (except when using a microwave). For breaded fish, you can lightly oil the dish holding the fish, but don't cover it or the breading will turn soggy.

When reheating fish, take into account the thickness and the variety of the fish. According to Cook's Illustrated, thick fish fillets of at least 1 inch reheat better than thinner ones: "Swordfish, halibut and salmon steaks reheat nicely, retaining their moisture well and with no detectable change in flavor." Thin fish like trout require extra care when reheating, because they often overcook and dry out.

Methods for Reheating Fish

Microwave: A quick way to reheat cooked fish is by warming it in the microwave. Set the microwave to a low power mode – 30-40 percent of full power – and microwave the fish in 30-second spurts until heated through. Flip the fish over while warming it to ensure it heats evenly. (Fish etiquette tip: Save your fish leftovers for home, not the office where coworkers with sensitive noses may find your fish-heating habits to be an assault on the senses.) Microwaving is a good option for baked, stewed or sautéed fish.

Toaster Oven: Using a toaster oven works particularly well for reheating breaded and fried fish. If you're worried that food will dry out, just cover it with foil. Aim for a low-temperature oven (no more than 350 F), and check on it once in a while until it's heated through. Fried foods have the best chance of re-crisping in the dry heat of an oven or toaster oven. Breaded ingredients should also be reheated here.

Oven: You can also reheat fish in the oven, pre-heating it to a temperature of 325 F. Cover the fish in foil if unbreaded or leave it uncovered if breaded. Heat it in the oven for 15–20 minutes or until it reaches the desired internal temperature (158 F or higher).

Stovetop: Fish stews and sautéed fish can be reheated on the stovetop using the same method in which they were first cooked. Just reheat to the desired temperature. Sautéed, grilled and baked fish can also be steamed on the stovetop: Loosely wrap the fish in foil, then place in a steamer or in a rack or basket over water in a covered pot and let the water come to a boil. Steam for 5 minutes or less, depending on the thickness of your fish. Just be careful not to scald yourself when checking the fish temperature. Remove the lid toward the wall away from your face, use a silicone baking mitt to handle the hot steam basket (hot condensation may soak through cloth mitts) and use tongs to remove the food from the steamer.