The jury also convicted Arthur Yavelberg, of Reston, for conspiracy to trade in misbranded food. He faces up to a year in prison.
Lam imported the frozen fish under false labels such as flounder and snakehead. He then sold it as basa, a trade name for a more expensive catfish.
The investigation began in 2005 and has resulted in a dozen convictions.
A tariff was imposed on Vietnamese catfish in 2003 after American catfish farmers complained the fish were being dumped.