How to Make It
Heat the olive oil in a large enameled cast-iron casserole. Add the leeks, onion, carrot and garlic and cook over moderately low heat until softened but not browned, about 10 minutes. Add the tomatoes, bell pepper, oregano, paprika and bay leaf and cook, stirring, for another 3 minutes. Pour in the diluted clam juice and wine and season with salt and pepper. Cover and simmer over low heat for 20 minutes.
Meanwhile, in a medium saucepan, boil the potatoes in salted water until tender, about 15 minutes; drain.
Bring the soup to a boil. Add the cooked potatoes, sea bass, mussels, clams and shrimp. Cover and simmer over moderate heat until the clams and mussels open; remove them with tongs as they are done. Continue cooking until all of the fish is cooked through, about 8 minutes total. Return the clams and mussels to the casserole. Sprinkle with the minced cilantro and scallions and serve.