Heat the oil in a Dutch oven or stockpot, add the onions, potatoes, fennel, salt, and pepper, and saute over medium - low heat for 15 minutes, until the onions begin to brown. Add the wine and scrape up the brown bits with a wooden spoon. Add the tomatoes with their juices, stock, garlic, and saffron to the pot, bring to a boil, then lower the heat and simmer uncovered for 15 minutes, until the potatoes are tender. Add the shrimp, fish, and mussels, bring to a boil, then lower the heat, cover, and cook for 5 minutes. Turn off the heat and allow the pot to sit covered for another 5 minutes. The fish and shrimp should be cooked and the mussels opened. Discard any mussels that don't open. Stir in the Pernod, orange zest, and salt to taste. Serve ladled over one or two slices of toasted baguette.