Cook the fish:
Preheat the oven to 425°. Transfer the fish to a heavy rimmed baking sheet so it stands upright. To keep the fish stable, splay the belly flaps and set a crumpled foil ball under the tail. Roast the fish for 30 minutes, until the flesh just flakes. Transfer the fish to a platter. Using 2 forks, lift the fillets off the bones and serve.