This is a rich seafood gumbo that can be made with whatever combination of seafood suits you. I'd choose shrimp and/or crab, plus some fish. Smoked fish or smoked oysters is a good choice. too. You need to make a broth for this recipe. Use this crab broth recipe, adding fish bones or shrimp shells to it if you have them.
Heat the seafood broth in a pot. You want it steaming, not simmering. In another large soup pot, heat the oil and bacon fat over medium-high heat. Stir in the flour and make sure there are no lumps. Cook this roux until it is the color of dark chocolate, which will take anywhere from 40 minutes to an hour. You will want to use a wooden spatula or spoon to stir. You will also want to lower the heat as the roux browns, until its at low heat when the roux is ready. Drink beer and listen to Cajun music while doing this. It helps.
When the roux is ready, add the chopped onion, pepper and celery to the pot and mix well. Cook this, stirring often, for about 5 minutes.
Stir in the garlic powder, paprika, chili powder, pepper, oregano, cayenne and celery seed. Ladle in some seafood broth and mix well. Turn the heat up to medium-high, and keep stirring in the seafood stock until the gumbo thins out. Typically you will need anywhere from 6 to 9 cups.
Add salt to taste and simmer gently for 30 minutes to an hour, stirring from time to time. The roux should not break, but if oil starts pooling on the surface of the gumbo, skim it off.
Add all the seafood and the file powder. Simmer this gently for 15 minutes. Add salt and hot sauce to taste and serve, garnished with the green onions, along with some rice or potato salad.
If you don't have bacon fat lying around, just use 1 1/2 cups of peanut oil.