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1
Toast fennel seeds in heavy small skillet over medium-high heat until fragrant and beginning to brown. Using spice grinder, coarsely grind fennel seeds with 1 1/2 teaspoons coarse salt. DO AHEAD:
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2
Cover and store at room temperature.
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3
Finely grate enough orange peel from 1 orange to measure 1 1/2 teaspoons; set aside. Using small sharp knife, cut off peel and white pith from 3 oranges. Working over bowl, cut between membranes to release orange segments into bowl. Squeeze enough juice from remaining 2 oranges to measure 1/2 cup. DO AHEAD:
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4
Cover separately; let stand at room temperature.
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5
Position 1 rack in top third and 1 rack in bottom third of oven; preheat to 400u00b0F. Brush large rimmed baking sheet with oil. Toss sliced fennel, 1 1/2 tablespoons oil, 1 teaspoon fennel salt, and 1/2 teaspoon orange peel in large bowl. Transfer to prepared sheet, spreading evenly. Roast fennel on bottom rack until beginning to soften, about 8 minutes.
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6
Meanwhile, brush large shallow roasting pan with oil. Mix 2 tablespoons oil, 1 teaspoon orange peel, and garlic in small bowl. If using fish fillet with skin, place skin side down in pan and brush top with orange-peel mixture. If using 4 skinless fillets, brush both sides with orangepeel mixture and place in pan, spacing apart. Sprinkle fish with 1 teaspoon fennel salt.
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7
Stir fennel; arrange orange sections around. Transfer fennel to top rack of oven and place fish on bottom rack. Roast until fish is just opaque in center and fennel is tender, about 13 minutes longer.
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8
Transfer fish to platter; tent with foil. Place same pan over 2 burners; heat over medium-high heat. Add shallot; stir until tender, about 2 minutes. Add wine and orange juice; boil, scraping up browned bits on bottom of pan, until reduced to 1/2 cup, about 4 minutes. Whisk in remaining 1 tablespoon oil. Season sauce with 1/2 teaspoon fennel salt, adding more to taste if desired. Arrange fennel and oranges around fish on platter. Pour sauce over, sprinkle with reserved fronds, and serve.
