In a large pot, heat the olive oil over medium heat. Add the chopped onion, garlic, fennel, and carrot. Sauté for about 5-7 minutes until the vegetables are softened.
Stir in the diced tomatoes, fish stock, saffron, thyme, bay leaf, salt, and pepper. Bring the mixture to a simmer and let it cook for 10 minutes.
Add the chunks of white fish to the pot and simmer for an additional 5 minutes.
Add the shrimp and mussels to the pot. Cover and cook for another 5-7 minutes, or until the mussels have opened and the shrimp are cooked through.
Remove the bay leaf and stir in the chopped parsley. Adjust seasoning with more salt and pepper if needed.
Serve hot with lemon wedges and crusty bread on the side.