In a large pot heat the olive oil over medium heat. Add onions, carrot, celery and garlic and cook until clear and translucent. Add bay leaf, thyme, parsley, fish stock, and canned tomatoes and bring to a simmer. Cook for about 20 minutes until vegetables are soft.
Add mussels, clams, shrimp, and oysters and oyster liquor. Cook for 3-5 minutes or until all shellfish has opened. Remove from heat and season to taste with salt and pepper and serve immediately.