Season fillets with salt and pepper. Dust fillets with 1/3 cup flour.

Beat buttermilk and egg in a bowl until combined. Stir together 1/2 cup flour, cornmeal, seafood seasoning, baking powder, and baking soda in another bowl. Dip flour-dusted fillets into egg mixture, then into seasoned flour mixture.

Heat oil over medium-high heat in a large frying pan or deep fryer to 350 degrees F (175 degrees C).

Working in batches, fry fillets in hot oil until golden, about 2 minutes per side. Transfer to a paper towel-lined plate to drain. Season immediately with salt after frying.