Preheat an oven to 200ºF. Place wire racks on 2 baking sheets and set aside.
Fill fryer to appropriate level and set temperature to 350ºF.
In a wide bowl, mix corn flour, salt, pepper and cayenne. Dip each catfish fillet into the seasoned corn flour, coating it all over, but shaking off any excess. Carefully lower each fillet into the oil. Fill the fryer, but do not crowd it. The oil should bubble up around each piece of fish. Monitor oil temperature closely to keep between 365ºF and 375ºF. Fry fillets until they are golden brown, about 2 or 3 minutes per side depending on thickness.
Using a wire mesh strainer or any tool that will allow you to hold the fish over the fryer as excess oil drains back into the kettle), remove fillets in the same order in which they were immersed. When fish stops dripping, immediately place it on the prepared baking sheet; when all fillets have been removed to the sheet, place in the preheated oven.
Always wait for oil to reach the proper temperature again before adding more food to it. Continue frying until all of the fish is fried. Serve immediately.