Slice fennel bulb thinly and lay on a platter along with its stalks and fronds. Lay fish on top in a single layer and sprinkle with remaining ingredients. Turn several times to coat. Let stand at room temperature, lightly covered, 2 hours (chill if longer than 2 hours, and use within 4 hours).
Make fish stock, rouille, and toasts while fish marinates.
*For more on these fish, including their other names, see "Buying Guide" (below).
When choosing your seafood, try to vary the textures and flavors. Some should be firm, others soft; some mild, others briny. Find them at a good seafood shop or your farmers' market.
Alaskan snow crab legs: Very firm, lobsterlike texture; sweet and mild. Usually only available cooked.
California mussels: Briny flavor; soft, melting texture with a bit of chew.
California squid (calamari): Firm but tender; sweet yet meaty. It's neither fish nor shellfish, really, but it gives great texture and flavor to the soup.
Dungeness crab: Flaky; sweet and moist.
Pacific cod (true cod, gray cod): Delicate; mild flavor.
Pacific halibut: Firm, with mild flavor.
Petrale sole: Delicate texture; mild, sweet flavor.
Rockfish (black bass, sea bass, black snapper): Medium-firm; clean sea flavor.
Sablefish (black cod): Silky, medium-firm; rich, buttery flavor.
Spiny lobsters: Succulent and firm. Can use, cooked, instead of crab. Available from fall to spring.
Spot prawns: Incredibly sweet taste and tender-crisp; keep head and tail on for the most flavor. Can be hard to find.