In a large pot, heat the oil. Add the onion, celery and carrot and cook over moderately high heat until softened, 5 minutes. Add the garlic, orange zest, thyme sprigs, fennel and coriander seeds and saffron and cook over moderate heat, stirring, until fragrant, 5 minutes. Stir in the tomato paste and cook over high heat until glossy, 1 minute. Add the tomatoes, clam juice, wine and port and bring to a boil. Add the grouper and shrimp, cover partially and simmer for 45 minutes. Discard the zest and thyme sprigs.
Working in batches, transfer the soup to a food processor and pulse until coarsely chopped. Rinse out the pot. Set a food mill fitted with a coarse blade over the pot and run the soup through the food mill. Bring the soup to a simmer. Stir in the Pernod and season with salt and pepper. Ladle the soup into bowls and serve.