1. A day ahead, sprinkle the fish on both sides with salt and place the fillets in a deep glass, enameled or stainless-steel baking dish large enough to hold them in one layer.
2. Cover with plastic wrap and refrigerate 8 hours or overnight. Then remove any remaining bones with tweezers.
3. In a small bowl, combine the vinegar, water and sugar, and pour over the fish. Marinate at room temperature for 15 minutes. Then place the fish on a cutting board and slice the fish diagonally into ½-inch-wide pieces.
4. Divide the fish into 4 portions and arrange the slices side by side on individual plates or in small soup bowls. Garnish each portion with 2 tablespoons of namasu and a sprig of parsley.
5. Sprinkle each serving of fish evenly with grated ginger and accompany with individual bowls of sambai-zu.
6. Shime saba will serve four as a first course or as part of a Japanese meal or it will serve two as a main course for lunch.
