Feel free to improvise with whatever fish and shellfish looks good and fresh. I like to use a firmer white fish such as monkfish or halibut, along with shrimp, scallops, and clams. I doubt you’d hear any complaints if you tossed in a few mussels or swapped out the shrimp for lobster. Serve Zuppa di Pesce with garlic-rubbed crostini.