n my lifetime, fish that were as common as dirt, such as Atlantic cod, haddock, and scrod, have been brought to the brink of extinction. Others that no one cared to eat or even knew about have replaced them, often only briefly, before they, too, practically disappeared. Once déclassé (on this side of the Atlantic at least), the arriviste monkfish scaled the social ladder to the toniest restaurant tables, awash in saffron broths and in red-wine matelotes. A favorite of French chefs, it is now overfished. Remember redfish? Louisiana chef Paul Prudhomme's recipe for blackened redfish blazed across the country (igniting a few kitchen fires along the way), creating so great a demand for Gulf red drum that the fishery collapsed. It is still recovering. Before the 1980s, who outside of Australia and New Zealand had ever heard of orange roughy? With its bland, snow-white flesh, it was the ideal fish for people who didn't really like fish, and soon roughy fillets were in every supermarket frozen-food case. No one realized until it was almost too late that roughy, a slow-growing, long-lived species, were being wiped out before they could reproduce. Atlantic swordfish had been in alarming decline for years before prominent chefs signed on to the successful "Give Swordfish a Break" campaign in 1998. (Pacific swordfish was abundant and still is, as far as anyone knows.) When Chilean sea bass, a marketing name for two species of Patagonian and Antarctic toothfish, burst onto the restaurant scene in the early 1990s, it quickly became the chefs' darling for its unctuous flesh, which was almost impossible to overcook. Few knew how relentlessly it was pursued, or that its deadly bycatch was pushing some species of albatross toward endangerment. For years I ate sushi and sashimi every chance I got, savoring the buttery toro, or belly meat, of the bluefin tuna. But after reading Song for the Blue Ocean, marine biologist Carl Safina's searing 1998 elegy for the sea's great predators, I lost my taste for toro. The choices keep shrinking. What can a fish lover eat without putting the future of the species at risk?

When it comes to fruits, vegetables, poultry, and meat, it's easier. I shop at farmers' markets and buy from organic growers I know and trust. If I want to be sure that my chicken is antibiotic-free or that the cow that's now my ground round got to chew its cud outdoors at some point, then I look for the simple brown and green USDA organic label. But to date, there have been no comparably stringent labeling regulations governing seafood, not even for fish that are farmed. In February, the USDA announced that it would begin requiring almost all seafood to be labeled with its country of origin and where it was processed, but the program is aimed more at promoting the U.S. fishing industry than telling you where your fish really came from -- a "made in the U.S.A." tag for fish. It doesn't tell you whether it was caught off California or Massachusetts, or by a U.S. flagged trawler off South America for that matter. The USDA requirements will tell you whether a fish was wild-caught (but not how) or farmed (but not whether it was farmed sustainably).

Fish fanciers who care about such issues are on their own. Luckily there are a few detailed sources you can turn to the next time you're trying to decide between cooking moules à la marinière and pan-fried red snapper. (Choose the mussels -- as long as they're farmed -- every time. In the United States, the true red snappers of warm southern waters are depleted, their young often victims of shrimp nets in their native Gulf.) I recently dipped into One Fish, Two Fish, Crawfish, Bluefish: The Smithsonian Sustainable Seafood Cookbook. Accentuating the positive rather than the negative, it spotlights well-managed species and encourages consumers and cooks to look beyond the tired staples, such as farmed salmon and shrimp, and to experiment with some underappreciated (but nevertheless delicious) fish such as Atlantic cobia and Pacific grenadier. An authoritative seafood guide, it is also an ambitious cookbook with 150 recipes, both difficult and easy, from leading American chefs. (After slow-baking king salmon as Alice Waters of Chez Panisse does -- and serving it with her Meyer lemon relish -- I'll never slap a salmon on the grill again.)

I also turn to my increasingly tattered copy of Audubon's Seafood Lover's Almanac, a comprehensive, species-by-species guide to the state of the fisheries directed to the thinking consumer. The two books don't always agree (Smithsonian sees the domestic shrimp fishery through a rosier lens than Audubon does), but they are the indispensable PC bibles I reach for whenever I need help.

Back in my fish market, however, I face another problem: Should I be the angry crusader? As I move to the far end of the counter, there, to my dismay, is "Chilean sea bass" once again, and at a caviar price of $24.99 a pound. The manager of the market notices me and is quickly at my side. "Don't worry," he says reassuringly, "these fish are not actually Chilean sea bass because they're from Peru." I don't think for one moment he believes I'll fall for that, but I'm in no mood to argue so I just laugh. Instead, I narrow in on the luminously fresh northern Pacific halibut -- a well-managed species, say Audubon and Smithsonian. Commercial halibut fishermen must abide by individual quotas set by a U.S.-Canadian commission, and in Alaska, they reduce bycatch with scare devices that prevent seabirds from getting hooked on longlines. I feel that I've chosen well, but the payoff comes later on a plate. Underbroiled a little to keep the flesh moist and sweet, and drizzled with a tarragon butter sauce, this halibut can hold its own with any fish in the sea.