Frying too many fish in one pan and not leaving enough space for it to cook properly can result in mushy catfish fillet . Deep-frying the catfish in low heat can also affect the way the oil cooks the fish. Frying it in temperatures below and far above 350 degrees F can give you mushy catfish fillet. Although it’s much more tedious, make sure there is enough space to cook the fillets and that the oil is in the right temperature for cooking deep-fried, crunchy catfish.