Cut the fish in to chunks. Heat the oil in a large saucepan. Add the onion, leak, celery and garlic and cook gently for 5 minutes until soft. Add the chopped tomatoes , herbs de provence, orange rind, saffron strands and salt and pepper. Add the wine and stock and bring to the boil.
Reduce the heat, add the firmest fish and simmer for 5 minutes. Add the more delicate fish and the shellfish. Cover and simmer for 5 minutes until the fish is cooked through but still retains its shape and the mussels have opened. Discard any mussels that have not opened. Garnish with chopped parsley and serve.
Note: Use the fish and sellfish trimmings to make the stock