In a heavy-bottomed pot, melt the butter; add the carrots, onions, celery, potatoes, and corn and saute over medium-low heat for 15 minutes, or until the potatoes are barely cooked, stirring occasionally. Add the flour; reduce the heat to low and cook, stirring often, for 3 minutes. Add the Seafood Stock and bring to a boil. Add the seafood; reduce the heat and simmer, uncovered, for 7 to 10 minutes, until the fish is just cooked. Add the heavy cream, if desired, and the parsley. Add salt and pepper to taste, and serve.