Melt butter in a large saucepan over medium heat. Add flour and cook, stirring until the flour is brown and fragrant, about 1 minute.Advertisement
Add onion, celery, bell pepper, tomatoes and cayenne (if using); bring to a simmer. Cover and cook on medium-low, stirring occasionally, until the vegetables are very soft, about 15 minutes.
Sprinkle catfish with salt and place in the saucepan on top of the vegetables. Reduce heat to maintain a low simmer, cover and cook until the catfish is just cooked through and opaque, 8 to 10 minutes more. Remove from the heat.
Remove the catfish from the pan with a slotted spoon. Stir sour cream into the vegetables. Serve the catfish over the stewed vegetables.
1 vegetable, 3 lean meat, 1 fat