In a large saucepan or Dutch oven over medium heat, warm the olive oil. Add the leek and fennel and sauté until softened, about 5 minutes. Stir in the garlic and sauté for 30 seconds. Add the tomatoes with their juices, the fish stock, wine and thyme. Increase the heat to medium-high and bring to a boil. Reduce the heat to medium-low, cover partially and simmer for 1 minute to blend the flavors. Season with salt and pepper.