Soak the cleaned or filleted fish overnight in a gallon of water and I think 2 tablespoons of salt and 1 teaspoon of baking soda. Be sure to remove any dark meat when cleaning. Some people use malt vinegar for the soak. My local commercial fisherman uses a clear cold spring to clean out his live Tennessee River catfish. I think he leaves them in there for two or three days. They don't have a muddy taste at all.