First Vietnamese catfish are not catfish, then they are catfish. It all depends on which definition makes more money for US catfish farmers. Biology be damned, it's time for economics-based definitions of catfish.
In 2002, the US catfish industry got a law passed that defined Vietnames catfish as not-catfish. Then, an opportunity arose to get Vietnames not-catfish denied entry into the US if they got their catfish status reinstated. So now the US industry is seeking to restore rightful catfish status to Vietnamese catfish.
Nevermind whether these finny animals are really catfish or not.
And nevermind the real challenge for the US catfish industry, the competition and market position of their products. Look for delacata, the new name for US catfish.