Heat the oven to 450°F. Line a half sheet pan with parchment paper.
Rinse the fish inside and out with cold water and drain. Dry with paper towels. Stuff the body cavity with as much of the parsley, fennel, thyme, and citrus, as it can comfortably hold, saving a few lemon slices for garnish. Set aside.
Combine the kosher salt, egg whites, and water in a large mixing bowl and work it into a paste with your hands. Lay down a 1/2-inch-thick bed of the salt paste that's 1-inch larger than the fish on all sides. Lay on the fish and pile on the remaining salt paste, smoothing and mounding it to form a sealed dome approximately 1/2-inch thick all around. You may not use all of the paste.
Roast until the internal temperature of the fish registers 130°F, about 35 minutes. Remove from the oven and rest at room temperature for 10 minutes.
Open the fish at the table by hitting the dome several times with a small hammer and lifting off the slabs of salt. Brush away any stray salt. Gently pull out the dorsal (back) fin. Using a fish knife or serrated pie server, make a single incision all the way down the back of the fish and around the gill plate. Lift the skin off, working from the head to the tail. Remove the fillet, in pieces if necessary, from the top side of the fish, going down one side of the spine then the other. Grasp the tail and remove the skeleton, (it should come up intact). The meat revealed below will slide right off the skin.
Sprinkle the meat with a little olive oil and sea salt. Serve immediately.