Catfish that has been defrosted in the fridge can be kept for an additional 1 to 2 days in the refrigerator before cooking; catfish that was thawed in the microwave or in cold water should be cooked immediately. How long does catfish last in the fridge once it is cooked? Cooked catfish will usually stay good for 3 to 4 days in the fridge and 4 months in the freezer. How to tell if raw catfish is bad? The best way is to smell and look at the catfish: signs of bad catfish are a sour smell, dull color and slimy texture; discard any catfish with an off smell or appearance.