Pat the catfish fillets dry with paper towels. If your fillets have a dark, fatty line running through the center (the mud line), consider removing it with a sharp knife for a milder flavor profile.
In a shallow dish, whisk together the buttermilk and beaten eggs until smooth.
In a separate shallow dish, combine the cornmeal, flour, Cajun seasoning, garlic powder, onion powder, paprika, cayenne pepper, salt, and black pepper. Whisk thoroughly to distribute the spices evenly.
Dip each fillet in the buttermilk mixture, allowing excess to drip off, then thoroughly coat in the cornmeal mixture, pressing gently to adhere. For an extra-crispy result, let the coated fillets rest on a wire rack for 5 minutes before frying.
In a large, heavy skillet, heat oil to 350°F (175°C). Use enough oil to reach about ½ inch depth. Test the temperature by sprinkling a few cornmeal crumbs into the oil—they should sizzle immediately but not burn.
Carefully place the coated fillets in the hot oil, working in batches to avoid overcrowding. Fry for 3-4 minutes per side until golden brown and the internal temperature reaches 145°F (63°C).
Transfer the fried fillets to a paper towel-lined plate to drain excess oil. While still hot, sprinkle with a pinch of salt if desired.
Serve immediately with lemon wedges and garnish with fresh parsley.