In a Dutch oven over medium heat, warm the oil until shimmering, 1 to 2 minutes. Add the pancetta and cook, stirring occasionally, until beginning to brown, 3 to 5 minutes.
Stir in the fennel bulb, onion, celery, and salt and cook until vegetables are softened and lightly browned, 12 to 15 minutes.
Stir in the garlic, paprika, pepper flakes, and saffron and cook, stirring, until fragrant, about 30 seconds.
Pour in the wine, scraping up any browned bits. Stir in the water, clam juice, and bay leaves. Bring to simmer and cook until the flavors meld, 15 to 20 minutes.
Remove from the heat and discard the bay leaves. Nestle the fish into the cooking liquid and then spoon some cooking liquid over the top. Cover the Dutch oven and let the fish sit, off the heat, until the fish flakes apart when gently prodded with a paring knife and registers 135°F (57°C), 8 to 10 minutes.
Gently stir in the parsley, fennel fronds, and orange zest and, if desired, break the fish into large pieces. Season with salt and pepper to taste. Serve, drizzling individual portions with addition oil, if desired.