When we fry up our catfish here we generally use Zatarans seasoned fish fry. For the actual batter I use:

1 Egg
1/3 to 1/2 Can of beer (Diet Coors in my case )
1 Tablespoon of milk
1/8 to 1/4 Cup Yellow mustard (to taste)

Put the fresh caught fish into the mustard batter and roll through the Zatarans. Drop into hot oil (360-370 degrees) and enjoy!