Step 1

Preheat oven to 250 degrees. Line a large rimmed baking sheet with foil; fit another with a wire rack. In a large bowl, whisk together egg whites, 2 teaspoons salt, and 1/4 teaspoon pepper; add fish, and toss to coat. In another large bowl, combine cornmeal and flour; season with salt and pepper.

Step 2

Working in batches, lift fish from egg-white mixture (letting excess drip off), and dredge in cornmeal mixture, patting to adhere; transfer to foil-lined sheet.

Step 3

In a large skillet, heat oil over medium-high. Working in batches, cook fish until golden brown and opaque throughout, 4 to 6 minutes, turning once (if fish is browning too quickly, reduce heat). Transfer to wire rack, and keep warm in oven while remaining fish cooks. Serve with ketchup.