In a large stock pot, place the water, smelts, onion, quartered carrot, leek, celery, parsnip, bouquet garni, and salt and pepper, and bring to a boil over high heat, periodically skimming off the foam as it rises to the top. Cover the pot, reduce the heat, and simmer for 35 minutes. Strain the stock through a fine sieve into a clean pot, pressing the solids with the back of a spoon to extract as much liquid as possible. Discard the solids. Return the stock to the heat and add the salmon trimmings, wine, potatoes, and thin carrots. Bring to a boil, then reduce the heat to low and simmer, covered, until the vegetables are tender, about 25 minutes. Strain the stock into a clean pot, discarding all the solids except the potatoes and all the carrots. Rinse the potatoes and carrots being careful not to mash them, and set aside. Return the stock to low heat and simmer for several minutes. Add the egg white and shell and increase the heat to medium high. Bring to a boil, beating constantly, with a wire whisk. When the stock boils, the egg white will start rising to the surface. At this point, turn off the heat and let stand for five minutes. Line a colander with a double layer of dampened cheesecloth and strain the stock into a clean pot. Add the fish fillets to the stock and poach over medium low heat until cooked through; five minutes. Taste and adjust the seasonings. Halve the reserved potatoes and cut into wedges. Cut the carrots into fine dice. Divide the fish fillets among six soup bowls. Add a few potato wedges and diced carrots to each bowl. Ladle the stock into the bowls, sprinkle with scallions, and garnish with lemon slices.