Preheat the oven to 425 degrees F.
Pour the sea salt into a large bowl, add the egg whites, and mix vigorously until all the grains of sea salt are coated with egg whites. Spread 1/3 of the salt mixture over the bottom of a large rectangular or oval oven dish big enough to hold the whole fish. Place the fish on top, then cover it completely with the rest of the salt. No part of the fish should remain uncovered.
Place the dish in the oven, reduce the heat to 400 degrees F, and cook for 30 to 40 minutes, depending on the thickness of the fish; generally, cook for 10 minutes for every inch of thickness at the widest part of the fish.
Remove the fish from the oven. Crack the crust at the table with the handle of a knife or a small hammer. Serve with lemon wedges and drizzled with olive oil.