Heat the olive oil in a large, heavy pot over medium heat. Saute leeks, garlic, onion, celery and mushrooms until onions are soft, about 5 minutes. Add stock, tomato sauce, and wine. Bring to simmer, and season with cayenne and salt totaste. Add clams and mussels to pot if using. When they are almost cooked, add fish and remaining seafood, and simmer until all is tender. Garnish with parsley.