Peel shrimp; place shells in a saucepan. (Refrigerate shrimp until ready to use.) Add celery ends and onion peel to pan; chop remaining celery and onion, and reserve. (Using the leftover bits of onion and celery will layer the flavor and result in a flavorful broth.) Add broth; bring to a boil over medium-high heat. Reduce heat to low; simmer 30 minutes.
Meanwhile, cook sausage in a large Dutch oven over medium-high heat, stirring often, 7 to 8 minutes or until browned. Remove sausage; pat dry. Wipe Dutch oven clean. Sauté celery, onion, and peppers in hot oil in Dutch oven over medium-high heat 5 to 7 minutes or until onion is tender. Add garlic, and sauté 45 seconds to 1 minute or until fragrant. Stir in potatoes, next 4 ingredients, and sausage.
Pour broth mixture through a fine wire-mesh strainer into Dutch oven, discarding solids. Increase heat to high, and bring to a boil. Reduce heat to low, and cook, stirring occasionally, 20 minutes or until potatoes are tender.
Add fish; cook 2 to 3 minutes or until just opaque. Add shrimp, and cook 2 to 3 minutes or just until shrimp turn pink. If desired, stir in crawfish, and cook 2 to 3 minutes or until hot. Add salt and pepper to taste.
Spoon seafood into warmed soup bowls. Top with broth mixture. Serve immediately with Griddle Corn Cakes and Spiced Mayonnaise.
Outstanding!!! Simple ingredients that all come together superbly!!! The really amazing thing is that it's hearty yet light because you don't have to make a roux. I am looking forward to making this for my family for the week of Thanksgiving!!!