This fish stock recipe is from "Spain: A Culinary Road Trip," featuring Mario Batali with Gwyneth Paltrow, and is used to make Fideos with Seafood.
Place all ingredients in a large stockpot with enough cold water to cover. Bring to a simmer over medium-high heat. Skim off foam and discard. Reduce heat and simmer gently, uncovered, for 25 minutes, skimming off foam as necessary. Strain through a fine-mesh sieve. Let cool and refrigerate until ready to use, up to 1 week.