In a large bowl, combine 1 tablespoon oil, the lemon juice and sugar; season with salt and black pepper. Add the cabbage, carrot and onion; toss to coat.
In a large, shallow bowl, combine the cornmeal, cayenne and 1 teaspoon salt. Coat the catfish with the seasoned cornmeal, shaking off any excess.
In a large nonstick skillet, heat the remaining 1/4 cup oil over medium-high heat. Working in batches, add the fish and cook, turning once, until browned, about 5 minutes; drain on a paper-towel-lined plate. Serve with the carrot-cabbage slaw and the lemon wedges.