As the Monterey Bay Aquarium's vice president, Michael Sutton, put it during a morning panel at the Smithsonian Institution last weekend, "Sustainability is like pornography: It's hard to define, but you know it when you see it."

WASHINGTON — Deciding what constitutes sustainable seafood can be hard. As the Monterey Bay Aquarium's vice president, Michael Sutton, put it during a morning panel at the Smithsonian Institution last weekend, "Sustainability is like pornography: It's hard to define, but you know it when you see it."

The panel — part of a two-day series of tastings and discussions that brought chefs, scientists, fishermen and fish purveyors from across the country to Washington — underscored the complex choices consumers face in restaurants and supermarkets in light of the world's dwindling fish stocks. Organized by the Smithsonian Associates and the National Museum of Natural History, "A Guide to Picking Wisely From the Sea" exhorted attendees to use the power of the market to ease the pressure on vulnerable marine species.

Jeff Black, who owns and operates Addie's, Black's, Black Market Bistro and BlackSalt Fish Market and Restaurant here, urged the public to "move off the tuna-salmon-swordfish mentality" and try other species. He and other experts suggested such choices as sardines, farmed-raised shellfish and Alaskan black cod to prevent overfishing of more-popular fish stocks.

"As human beings, we can wipe out everything," Black said. "When you spend your money, you are making a choice. You're voting with your dollar."

As seafood consumption has risen worldwide and several commercial fish populations have crashed, the conservation and business communities have responded in a variety of ways.

The Marine Stewardship Council uses a third-party verification system to determine that the fisheries that receive its seal of approval are run responsibly; Whole Foods Markets require suppliers to fill out extensive paperwork and also sell MSC-certified goods.

And while many aquaculture operations have come under fire for harming the ocean rather than helping it, a number of fish farmers who attended the event said they offer a partial solution to the current seafood crisis. Maryland's Marvesta Shrimp Farms raises shrimp on five acres in a contained system that produces no effluent and requires no chemicals, antibiotics or hormones; North Carolina's Sunburst Trout Farm produces half a million pounds of rainbow trout a year on just seven acres.

Sally Eason, Sunburst's chief executive, said the seafood market requires fish farmers such as herself as well as traditional fishermen to meet the public's demand for fresh fish.

"It needs to be farmers and hunters," she said, adding that she still abides by the mantra her father adopted when he established her family's trout farm: "We'll be all right as long as we use what we've got and don't lose what we've got."

Such aphorisms came the closest to giving participants a sense of what it means to eat sustainable seafood. When Sutton offered a basic principle of fisheries management — "if you don't kill them, they tend to get bigger" — the program's host, Food Network star Alton Brown quipped, "Shocking. That's true for children, too."

Attendees who made it to the program's Friday night tasting reception or Saturday four-course lunch got to try plenty of sustainable seafood: Restaurant Nora's Benjamin Lambert offered up sake-glazed Alaskan black cod with a gingered kabocha squash puree, and Willow Restaurant's Tracy O'Grady and Kate Jansen served sauteed Kona kampachi with fresh chickpeas.

In the end, some of the consumers who attended the program said they still weren't sure what to eat or avoid when it comes to fish. Bob Kinkead, chef and owner of Kinkead's here, said their confusion illustrates the challenge that sustainable seafood presents.

"It's very simple: If we don't take care of the resource, it will be gone," he said. "The problem is that it's an enormously complex issue to solve."