Heat the oil in a very large pot over medium heat. Add the fennel, onion, shallots, and salt and saute until the onion is translucent, about 10 minutes. Add the garlic and 3/4 teaspoon of red pepper flakes
, and saute 2 minutes. Stir in the tomato paste
. Add tomatoes with their juices, wine, fish stock and bay leaf. Cover and bring to a simmer. Reduce the heat to medium-low. Cover and simmer
until the flavors blend
, about 30 minutes.
Add the clams and mussels
to the cooking liquid. Cover and cook until the clams and mussels begin to open, about 5 minutes. Add the shrimp and fish. Simmer gently until the fish and shrimp are just cooked through, and the clams
are completely open, stirring gently, about 5 minutes longer (discard any clams and mussels that do not open). Season the soup
, to taste, with more salt and red pepper flakes.
Ladle the soup into bowls and serve.