How to Make It
In a very large, enameled cast-iron casserole or Dutch oven, heat the 1/2 cup of olive oil. Add the fennel, celery, onion, oregano and crushed red pepper and cook over moderate heat, stirring frequently, until the vegetables are softened, about 15 minutes. Add the squid and cook over moderately low heat for 15 minutes, stirring occasionally.
Stir in the wine and bring to a boil over moderately high heat. Cook until evaporated, about 20 minutes. Stir in the tomato puree and strips of lemon zest. Season with salt and pepper and cook over very low heat, stirring occasionally, until very thick, about 40 minutes.
Add the water and clam broth and bring to a boil. Remove and discard the lemon zest. Season the broth with salt and pepper. Add the mussels, clams and shrimp, cover and cook until most of the shells have opened, about 5 minutes. Add the striped bass and cook until opaque, about 2 minutes longer.
In a small bowl, combine the parsley with the grated lemon zest. Spoon the stew into deep bowls and sprinkle with the gremolata. Drizzle with olive oil and serve.