Step 1

Combine shrimp shells and 3 cups water in a medium saucepan. Bring to a simmer over medium. Remove from heat, and let stand 15 minutes. Pour mixture through a fine wire-mesh strainer into a bowl; discard solids. Set stock aside. Toss together catfish pieces and salt in a large bowl. Cover and chill until ready to use, up to 1 hour.

Step 2

Heat oil in a large Dutch oven over medium. Add flour; cook, whisking constantly, until smooth and lightly browned, about 1 minute. Add onion, bell pepper, celery, and garlic. Cook, stirring often and scraping bottom of Dutch oven to prevent scorching, until softened, 8 to 10 minutes. Stir in shrimp stock, tomatoes with juices, okra, Worcestershire, thyme, bay leaves, Creole seasoning, and black pepper. Bring to a simmer over medium-high. Reduce heat to medium-low; cover and simmer until okra is almost tender, about 15 minutes.

Step 3

Stir in catfish and shrimp, and reduce heat to low. Cover and cook until catfish and shrimp are cooked through, 5 to 8 minutes. Remove and discard bay leaves. Season to taste with salt and pepper. Serve with black rice; garnish servings with scallions, and drizzle with olive oil.