For Tran Vu Long, who lives atop his floating catfish trap on the Mekong River near the border with Cambodia, the recent biannual harvest day was not the joyous payday it usually is. Mr. Long, a 35-year-old Vietnamese catfish farmer, sold his flapping fish - 40 tons' worth, all painstakingly weighed and carried in bamboo buckets onto the trading company's launch - at a loss of some $2,000, a small fortune here.

Mr. Long, who stood sullenly to the side as his hired hands scooped out seemingly endless gaggles of fish from underneath the space that doubles as his living room, has Washington politicians to blame. "The United States preaches free trade, but as soon as we start benefiting from it, they change their tune," he said

…The normalization of ties between Hanoi and Washington brought American trade missions bent on expanding Vietnamese free enterprise. One of these delegations saw in the Mekong Delta's catfish a golden export opportunity, with the region's natural conditions and cheap labor affording Vietnam a competitive advantage. Sure enough, within a few years, an estimated half-million Vietnamese were living off a catfish trade nurtured by private entrepreneurs. Vietnam captured 20 percent of the frozen catfish-fillet market in the United States, driving down prices. To the dismay of the Mississippi Farm Bureau, even some restaurants in that state - the center of the American catfish industry - were serving the Vietnamese species.

Soon Mr. Long and the other Vietnamese farmers were caught in a nasty two-front war being waged by the Catfish Farmers of America, the trade group representing Mississippi Delta catfish farmers. The Mississippi catfish farmers are generally not huge agribusinesses, and many of them struggle to make ends meet. But that still does not explain how the United States, the international champion of free market competition, could decide to rig the catfish game to cut out the very Vietnamese farmers whose enterprise it had originally encouraged.

Last year, with the aid of Trent Lott, then the Senate majority leader, the American catfish farmers managed to persuade Congress to overturn science. An amendment, improbably attached to an appropriations bill, declared that out of 2,000 catfish types, only the American-born family - named Ictaluridae - could be called "catfish." So the Vietnamese could market their fish in America only by using the Vietnamese terms "basa" and "tra."

That was only the first step in a bipartisan assault. Congressman Marion Berry, an Arkansas Democrat, joined in a stupendously tactless disinformation campaign against the Vietnamese, suggesting that their fish were not good enough for American diners because they came from a place contaminated by so much Agent Orange - sprayed over the countryside by American forces during the Vietnam War. Catfish Farmers of America, for its part, ran advertisements warning of a "slippery catfish wannabe," saying such fish were "probably not even sporting real whiskers" and "float around in Third World rivers nibbling on who knows what."

Not satisfied with its labeling triumph - an old trade-war trick perfected by the Europeans - the American group initiated an antidumping case against Vietnamese catfish. And for the purposes of this proceeding, Congressional taxonomy notwithstanding, the fish in question were once again regarded as catfish, not basa or tra. (Don't try explaining to Mr. Long how two branches of the American government, conveniently enough, can simultaneously maintain that his fish are two different creatures.)

…In this case, the Commerce Department had no evidence that the imported fish were being sold in America more cheaply than in Vietnam, or below their cost of production. But rather than abandoning the Mississippi catfish farmers to the forces of open competition, the department simply declared Vietnam a "nonmarket" economy. The designation allowed it simply to stipulate that there must be something suspect going on somewhere — that Vietnamese farmers must not be covering all the costs they would in a functioning market economy. Tariffs ranging from 37 percent to 64 percent have been slapped by the department on Vietnamese catfish.