In a large frying pan over low heat, warm the oil and add the fennel seeds, garlic and bay leaves and cook gently, stirring frequently, until nice and fragrant.
Stir in tomato paste, then pour in the wine & stir. Cook for 2-3 minutes over low heat, then transfer contents of pan to slow cooker.
Cut off stem and feathery tops of fennel bulb, then cut the bulb into lengthwise strips, then in half, making sure to leave the core intact on each piece so the bulb holds together.
Add the fennel wedges, crushed tomatoes, stock and salt & pepper and sugar to the slow cooker, stirring everything together, and cook on low for 2-3 hours.
Add the fish, couscous and orange zest towards the end of the final cooking stage, and cook for an additional 30 minutes.
Serve as is, or ladle out 2 cups of the broth, and blend. Add back in for a thicker texture soup.