The catfish po' boy is the rare fried po' boy where the coating, not the filling, sets the whole sandwich. The fillet is dredged in seasoned cornmeal rather than a wet wheat batter, and cornmeal fries into a sandy, gritty shell with a faint corn sweetness that flour cannot produce. Against the soft, fatty, mild flesh of the catfish and the near-hollow airy Louisiana French loaf around it, that grit is the entire identity. Swap the cornmeal for a flour batter and you have a generic fried-fish po' boy. Keep the cornmeal and you have this one.
The craft is in taming the fish before the fry and protecting the crust after it. Catfish carries a muddy edge that a buttermilk or hot-sauce soak both cuts and uses, because the wet film gives the dry cornmeal something to grip so the shell does not slough off in the oil. The fillet goes into hot fat for a short, decisive pass: long enough to set the gritty crust, short enough that a soft fillet does not go to mush inside it. It lands on the thin-crusted, glass-crackly New Orleans loaf, never the soft fish-camp bun, and the swap matters, because the loaf shatters cleanly under the bite and adds none of its own moisture to a coating that softens the instant it steams. Dressed means the local system applied as a counter rather than a flood: shredded lettuce, tomato, pickle, and mayonnaise, often with a remoulade or a shake of hot sauce worked in to put acid and fat against the lean, gritty fry. A po' boy shop runs the fryer hot and builds to order so the cornmeal is still crackling when the loaf closes.
The variations follow the dredge and the Delta. A blackened fillet drops the cornmeal for a dry spice crust and a hot skillet, which is no longer the same sandwich. A heavier cayenne in the meal pushes it toward a Delta heat; an étouffée build abandons the fry entirely for a thick stew in the same loaf. Those adjacent forms, like the wider po' boy family of shrimp, oyster, and roast-beef debris, are their own sandwiches and deserve their own articles rather than being crowded in here.