Preheat oven to 450 degrees with a rack in the center. Rinse fish thoroughly, inside and out, until no traces of blood remain. Pat fish dry with paper towels. Stuff cavity of fish with a few lemon slices, a few sprigs of parsley, a few sprigs of thyme, and a bay leaf; set aside.
In a large bowl, stir together salt and egg whites until thoroughly combined. Spread a 1/2-inch layer of salt, about the size of the fish, in a baking dish. Arrange the remaining lemon slices, parsley, thyme, and bay leaves over the salt; place fish on top of herbs.
Pour the remaining salt over fish, completely covering the body; the tail can stick over edge of pan. Using your fingers, pat down salt, completely sealing the fish.
Place pan in oven, and cook until fish is done, allowing 15 minutes per pound. (One way chefs check for doneness is to insert a carving fork or metal skewer through the salt crust and into the fish, then place the skewer to the chin under lower lip for 15 seconds; if the metal feels very warm the fish is done.) Remove pan from oven; let sit 5 minutes.
Gently break away the crust. Transfer fish to a cutting board. Using a paring knife and your fingers, peel away skin. Separate, and serve.