In a large dutch oven, heat oil, sprinkle flour using wire whisk, stir constantly until dark roux is created.
Once golden brown, add onion, bell pepper, and celery. Cook for 8-10 minutes.
Add Cajun Maispalm Seasoning and gumbo file. Slowly add shellfish stock. Simmer for 1 hour. Add shrimp, crabmeat, oysters with liquid to the gumbo, and return to a low boil. Cook for 10 minutes.
Add green onion, parsley, hot sauce, and adjust any seasoning as needed.
Serve over cooked rice.
Optional: You can add sliced andouille sausage to gumbo if you choose.