Swai is a freshwater fish native to rivers in Vietnam, and catfish is native to North American rivers. While the two fish do have a similar flavor when cooked, swai is different from the common catfish farmed and sold in the U.S. Swai and catfish are often mistaken because the common scientific name of swai is "Sutchi Catfish," and swai is commonly sold as imported catfish.
Swai is a type of South Asian catfish native to countries like Cambodia, Laos, Thailand and Vietnam. It's also sold under the names basa, tra or pangasius due to its Latin scientific name, Pangasius hypophthalmus. Some importers of South Asian catfish such as swai have been fined by the U.S. Food and Drug Administration for selling swai under the names catfish, grouper or sole to avoid tariffs on imported fish. Swai is often raised in cages in rivers; South Asian fisheries aren't regulated, so it can be contaminated.
Catfish in the U.S. (as regulated by the U.S. FDA) is actually two species of North American freshwater fish in the Ictaluridae family. Species of catfish farmed and sold in the U.S. are blue catfish, Ictalurus furcatus, and channel catfish, Ictalurus punctatus. Catfish are commonly farmed in large ponds or sometimes caught fresh from North American river deltas. Fish farms producing catfish in the U.S. are highly regulated to ensure that whole fish and fillets don't contain bacteria or disease.
Swai, a white-fleshed fish found in frozen fillet form at most fish markets and grocery stores, can be a good alternative to more expensive fish. When cooked, swai has a flaky texture and mildly sweet taste much like catfish. You can bake or broil swai with butter to enjoy the mild flavor. Swai can also be very tasty with Asian sauces or spicy flavors, or you can fry the fish fillets with a seafood breading or spiced breadcrumbs.
Because of its flaky texture, catfish is very versatile; it can be baked, broiled or fried. In the southern U.S., catfish fillets are often cut into strips and fried in cornmeal breading. Catfish can also be roasted or broiled whole after rubbing it with spices. Light sauces with butter or lemon flavors can offset the sweet flavor of baked catfish very nicely.