When trade with Vietnam resumed in 1994, U.S. seafood importers started shipping fillets from a Vietnamese catfish called basa, or bocourti. But most of what’s sold in the market today as basa isn’t basa. Real basa, P. bocourti, is one of 21 species in the Pagasiidae family of catfish found throughout Southeast Asia. Cambodian and Vietnamese fish farmers have raised basa in cages along the Mekong River for decades. But P. hypophthalmus, or swai, known locally as tra, has become the preferred farmed species. Inferior to basa, but faster and cheaper to raise, swai has been marketed as China sole, river cobbler and even basa, adding to the confusion of unwary buyers. Also labeled catfish, it was eagerly accepted as a cheap alternative to the farmed U.S. species. But such labeling is no longer allowed, following a Food and Drug Administration ruling that only species from the family Ictaluridae can be sold as true catfish.