Where in the world is that fish from?

At the Stop & Shop here in America's oldest commercial fishing port, Harold Williams loads groceries into his car. As he often does, Mr. Williams bought fish for chowder. He favors hake, or cusk when he can find it.

Freshness counts most, he says, then price. And country of origin? Williams pauses to give the issue some thought. "Wherever it's fresh," he says with a shrug. He's heard that Iceland moves quickly to ship its catch.

Frank McMahon, a seafood chef at Hank's, in Charleston, S.C., reports a different take.

"We have people asking all the time, 'Is it local? Is it domestic? Where does it come from?' " he says in a telephone interview. "If I say the crab is from Indonesia, there are people who will say, 'I don't want the crab cakes.' "

Whether they care to know or not, seafood consumers should find a new country-of-origin label today on all but canned and highly processed fish and shellfish. The label, required by the US Department of Agriculture (USDA), represents the first tangible fallout from the haltingly implemented farm bill Congress voted into law in 2002.

Called COOL - for country-of-origin label - it will ultimately extend to fruits and vegetables, peanuts, beef, pork, and lamb. One plank in a much broader farm bill, COOL is viewed by many farm and consumer groups as a boost to the buy-American movement. In the post-9/11 context, it also addresses food-supply safety.

With seafood, especially nonfarmed seafood, comes special complexity. In a catch's frantic journey from docks to auction houses to wholesalers, accurate identification by species - let alone by oceanographic origin - has proved tough to ensure. Now, fish caught in international waters will be attributed to the country whose flag the fishing boat (or factory ship) flies - unless, short of being canned, it is "substantially transformed."

"If the fish is caught by, say, a Chinese-flagged vessel, but then they take it to Taiwan and cut the head off and gut it and package it up, it would take the Taiwan country of origin," explains Kathryn Mattingly, spokeswoman for USDA's Agricultural Marketing Service. She calls the seafood label a bid to help consumers make informed choices.

But ease for consumers means unprecedented recordkeeping challenges for those along the supply chain. Accountability lies with retailers, who face fines of $10,000 a day for unlabeled or mislabeled imports.

The Food Marketing Institute (FMI) maintains that such labels should have remained voluntary, and that only consumer demand should drive changes. "Retailers have long been effective in giving consumers information on the products they buy," says Deborah White, associate general counsel for the FMI, adding that the industry is on course for compliance.

The USDA will allow for a period of several months during which the government will soft-pedal enforcement and focus on clarifying the policy as special cases arise.

Meanwhile, says Ms. White, retailers are likely to turn up the heat on suppliers, dumping them and looking elsewhere when country of origin can't be documented to their satisfaction.

Suppliers, too, are a reluctant party to COOL. The regulation is redundant, given existing customs and label rules of the US Food and Drug Administration and the Federal Trade Commission, says John Connolly of the National Fisheries Institute, a trade association in McLean, Va.

A package of tilapia from Costa Rica, for example, would long since have been so labeled, by law, before being shipped to stores, he says. Tightening rules at the retail level, he says, could actually limit consumer choice.

"[Retailers] might reduce the amount of seafood available at their seafood counter in order to reduce their risks," Mr. Connolly says. "If they have [typically had] Thai shrimp and Vietnamese shrimp and US shrimp, and shrimp from Belize, they might [now] just put out one - and it'll probably be the kind they sell the most of, which tends to be imported."

Domestic seafood doesn't always have an edge, especially with high-volume buyers. Mr. McMahon, the chef, buys local shrimp when he can, but seasonal limitations make it difficult. Imports often provide more consistent sizing, he says, which makes dishes easier to cook.

Connolly says the NFI urges suppliers to tout the unique culinary qualities of their regions' offerings - Alaskan wild salmon, Gulf shrimp.

Others, while hailing COOL, worry that too much emphasis on country of origin could trigger blunt consumer behavior in an area where nuance is important.

Already the Humane Society has encouraged US shoppers to use the new labels to avoid Canadian seafood because that country hunts seals.

But snow crab from Canada falls in the realm of "best practices" in terms of sustainability, says Jennifer Dianto, science manager of the Seafood Watch program at Monterey Bay Aquarium in California.

"I'd hate to see [COOL] used to make blanket statements," says Ms. Dianto, whose group produces a pocket guide that tracks international fishing practices and fish populations. Information about species and practices is detailed on the aquarium's website, www.mbayaq.org.

"But someone can now be held accountable," says Dianto. "Consumers can take a little comfort in that."