To prepare stock, heat 1 1/2 teaspoons oil in a large Dutch oven over medium-high heat. Add celery and next 4 ingredients (through quartered onion); sauté 4 minutes. Add thyme, parsley, and bones. Pour 5 cups water over mixture; bring to a boil. Reduce heat, and simmer 30 minutes. Strain stock through a sieve into a bowl; discard solids.
To prepare soup, wipe pan dry with a paper towel. Heat 2 tablespoons oil in pan over medium-high heat. Add 1 cup carrot, sliced onion, and 4 garlic cloves; sauté 4 minutes. Stir in tomato and next 4 ingredients (through salt); cook 1 minute. Add wine; bring to a boil. Cook 8 minutes or until liquid almost evaporates. Stir in stock; bring to a boil. Stir in mussels and fish. Cover and cook over medium-high heat 4 minutes or until mussels open and fish flakes easily when tested with a fork or until desired degree of doneness; discard any unopened shells. Remove from heat; stir in 1/3 cup parsley, oregano, and 1 tablespoon thyme. Serve immediately with lemon wedges.