Heat the olive oil in a large, heavy pot over medium-high heat. Add the garlic, onion, and fennel and saute until just brown, 5 to 10 minutes.

Add the saffron, tomatoes, and stock

Bring to a boil and cook until the vegetables are tender and the liquid is reduced by half, about 20 minutes.

Reduce heat to medium and add the fish (but not shellfish). Cook for about 2 minutes.

Add any clams, mussels, and shrimp. Simmer until the shells just begin to open, about 4 minutes more.

Cook until all shells have opened, the shrimp is pink and curled, and the fish flakes easily, about 2 minutes.

Serve from the pot, sprinkled with the parsley and topped with crusty bread and a dollop of rouille.