01 - In a shallow bowl, whisk together the buttermilk and hot sauce. Add the catfish fillets, turning to coat. Cover and refrigerate for at least 15 minutes (up to 1 hour) to marinate.
02 - In another shallow dish, mix the cornmeal, flour, Cajun seasoning, paprika, garlic powder, salt, and black pepper until well combined.
03 - Remove the catfish from the marinade, letting excess drip off. Dredge each fillet in the cornmeal mixture, pressing gently to coat well on all sides.
04 - Pour vegetable oil into a large skillet or deep fryer to a depth of about 1 inch. Heat oil to 350°F.
05 - Fry the catfish in batches, 3–4 minutes per side, until golden brown and cooked through. Do not overcrowd the pan. Transfer to a wire rack or paper towels to drain.
06 - Combine mayonnaise, pickles, capers, lemon juice, mustard, and parsley in a small bowl. Stir well and season with salt and pepper to taste.
07 - Serve the fried catfish hot, accompanied by tartar sauce and lemon wedges.