In a medium pot, boil half the potatoes and half the onion in 4 cups of fish stock until very soft. Purée in a blender or food processor and reserve.
In a large pot, gently sauté the remaining onion and the celery in butter until soft. Add white wine to the pan to deglaze. Add haddock and the remaining potatoes, the remaining fish stock, the basil, thyme, paprika and pepper.
Cook at a simmer until the potatoes are almost done, about 12-15 minutes. Add the rest of the seafood and cook for an additional 5 minutes; add the reserved potato mixture. Stir in cream and serve. Makes 4-6 servings.