Heat the oil in a large pot over medium heat. Add the fennel, onion, shallots, and salt and saute until the onion is soft and cooked . Add the garlic and red pepper flakes, and saute until golden.
Add tomatoes with their juices, fish stock and bay leaf. Cover and bring to a boil. Turn down the heat and simmer until the flavors blend, about 30 minutes.
Add the clams and mussels to the broth then cover and cook until the clams and mussels open.
Add the scallops,shrimp and fhalibut and simmer gently until the fish and shrimp are just cooked through, and the clams are completely open.
Check the seasoning and ladle into bowls and serve with crusty ciabatta.
