Preheat oven to 450°F with oven rack 6 inches from heat. Combine catfish and buttermilk in a medium bowl; cover and chill 20 minutes or up to 1 hour

Whisk together cornmeal, panko, Cajun seasoning, and 1⁄4 teaspoon of the salt in a shallow dish. Drain catfish; discard buttermilk. Working in batches, dredge fish in cornmeal mixture. Place fish on a wire rack set inside a rimmed baking sheet. Bake in preheated oven until it’s golden brown and flakes with a fork, 20 to 25 minutes.

Meanwhile, whisk together mayonnaise, lime juice, pepper, and remaining 1⁄2 teaspoon salt in a medium bowl. Add cabbage; toss to coat.

Place 2 pieces of catfish in each tortilla. Top with cabbage mixture, radishes, avocado, cilantro, and chives. Serve with lime wedges and hot sauce.