Heat olive oil in a large pot and sauté onion, fennel, garlic, and tomatoes until softened.
Add saffron, thyme, orange zest, and seafood stock, then bring to a gentle boil.
Simmer the broth for 20–25 minutes to develop the flavors.
Add firm white fish pieces and cook for 5 minutes.
Add shrimp, mussels, and other shellfish, cooking until the mussels open and the shrimp are fully cooked.
Season with salt and black pepper to taste.
Serve hot with toasted baguette and rouille.