Whether or not to reuse oil when frying foods is an ongoing debate between chefs of all types. When you throw fish into the equation, the opinions get stronger. Regardless of how many times you decide to use a batch of oil, the important thing is to employ good cooking and storage techniques to keep the oil safe and healthy.
Keeping It Pure
Most modern chefs agree that it is perfectly fine to save oil from a frying session. Turn off the heat immediately and strain out any bits and pieces of food in the oil. After the oil cools down, pour and store it in a sealed container at room temperature away from direct sunlight. However, it is usually not wise to use that oil for cooking a different type of food, especially when fish or seafood is involved. The odor and taste of seafood will carry over into your new dish and flavor it almost immediately.
The Telltale Signs
Look for signs that your oil is ready to be tossed out. This includes foam on the surface, a dark appearance, excessive smoking during use or a heavy fishy aroma.