Melt 2 tablespoons of the butter in a large skillet. Season the catfish fillets with salt and pepper and the cayenne. Coat the catfish fillets lightly with flour, then add them to the skillet and cook over moderately high heat, turning once, until golden brown on both sides and cooked though, about 10 minutes. Transfer the catfish fillets to a platter; tent with foil and keep warm.
Melt the remaining 4 tablespoons of butter in the skillet. Add the pecans and cook over moderately high heat, until the pecans and butter are browned and fragrant, about 3 minutes. Stir in the lemon zest and juice and season with salt. Spoon the pecan butter over the catfish fillets and serve immediately with lemon wedges.
Point up the lemony and nutty flavors in this catfish dish by serving a full-bodied but bright Pinot Gris from Oregon.