As populations of seafood favorites decline and environmental watch groups decry harmful fishing practices, fish fans need responsible alternatives. Chef Barton Seaver of Hook restaurant in Washington, D.C., schools us in the best sustainable choices.

High demand for Chilean sea bass has led to overfishing, while unregulated catch methods ruin the fish's deep-sea habitat, imperiling threatened seabirds, such as the albatross. Instead, try black cod (aka sablefish). Supplies of this Alaskan fish, a great source of omega-3s, are constantly managed to remain abundant.

High in mercury, Atlantic swordfish remains a struggling population despite signs of recovery. Fishing practices often kill or maim endangered sea turtles. Instead, try wahoo. With a flavor and texture somewhere between swordfish and tuna, it has a slightly lower mercury content than swordfish and limits have been placed on harvesting.

A staple for New Englanders and maritime Canadians for decades, Atlantic cod has been overfished to historically low population levels. The bottom trawling method used most frequently degrades the ocean floor. Instead, try Alaskan pollack. A cousin to cod, pollack is abundant, fertile, and fished with midwater trawls that don't destroy habitat or trap vulnerable species by mistake.

Snapper and grouper are both imported from Central America, where oversight can be slack. Fishing methods damage the coral reef habitats on which these fish depend. Instead, try tilapia. Domestic, low-mercury tilapia is farm-raised in closely regulated sites to avoid wastewater and pollution. Tilapia rarely needs antibiotics.