To clean the sardines, with a small sharp knife, remove the heads. Carefully slit open the belly and clean and gut the fish. Grasping the top of the spine, quickly pull to remove. Cut the 2 fillets separate from the tail. Wash under running water and pat dry.
Place in a single layer, skin side down, in a large shallow glass dish. Cover with the lemon juice (use more as needed to cover) and salt. Let marinate in the refrigerator for 4 to 24 hours, depending upon their size. (The fish are marinated when they turn almost completely white.)
Remove from the lemon juice, rinse and pat dry. Place the fillets in a clean shallow glass dish or platter.
In a bowl, whisk together the oil, shallots, parsley, and red pepper. Pour over the sardines, cover, and refrigerate for 1 to 2 hours. Bring to room temperature before serving.
Yield: 20 fillets, 4 to 6 servings