Make a roux with the flour and shortening. Cook flour and shortening in a large pot over medium-high heat until the flour turns brown and begins to smell nutty.
Add garlic and cook until golden brown. Add onion, bell pepper, and celery and cook until transparent.
Turn heat down to low, and add shrimp and tomato sauce, simmer 10 minutes, stir in water, and blend well.
Turn heat down to simmer and add all other ingredients except okra and oysters.
Cook for about 30 minutes add okra, and cook until the okra turns bright green.
Add oysters and cook 10 minutes longer. Serve in a soup bowl over steamed rice.
Recipe Tips
Do not use a cast iron pot to cook the soup, it will discolor the soup. Stainless steel, or a ceramic pot like Le Cruset is recommended.