Clean and gut fish, remove top and bottom fins, scale and remove gills. Whisk egg whites to soft peaks and fold in salt
Place lemon, limes and chopped fennel tops in body cavity and set aside
Place 4 tablespoons of egg white mixture on a large platter add a generous amount of dry kosher salt to bottom of pan suitable for oven to table use. Place fish on top of mixture and spoon remaining mixture over top of fish. Add mor dry salt to top
Place fish and platter in oven and bake for 25 to 30 minutes. remove and strike crust to crack.