Editor's Note: We're happy to introduce another blog feature today, a bi-weekly column by Environmental Defense. Every two weeks, Online Activism & Outreach Coordinator Jessica Bosanko will bring you news, information and action items about ED's efforts to "find innovative, practical ways to solve the most urgent environmental problems."

By Timothy Fitzgerald, Environmental Defense scientist

Seafood lovers who want safe and eco-friendly fish might need help sorting through the mixed messages out there. The issue is complex – but here's how to sort through it why to choose healthy, sustainably caught or farmed fish.

Eating even modest amounts of fish helps protect against heart disease and is essential to the developing brains of fetuses and young children. The federal government and the American Heart Association both recommend two servings of seafood a week to reduce the risk of heart disease and death from heart attacks. The greatest cardiovascular benefits come from eating fish high in long chain omega-3 fatty acids, such as small oily species like herring, and mackerel, and larger predatory fish like salmon and some tuna.

Fish are disappearing from the oceans

Sadly, even as the health benefits of eating fish are becoming clearer, the ocean's ability to provide plentiful seafood is diminishing.

Since the 1950s, when industrial fishing began in earnest, large fish have mostly disappeared from the oceans, plummeting by an astonishing 90 percent according to a 2003 analysis. If we continue current fishing practices, most fisheries will be exhausted by mid-century, a recent report concluded. Many of America's favorite seafood – Atlantic cod, sea scallops, flounder, grouper, snapper and more – are already overfished.

At the same time, health-conscious consumers worry about fish with toxins such as mercury, dioxins or PCBs. To avoid too much mercury, children and women of child-bearing age should be careful about how much large fish they eat, such as swordfish and shark. Some farmed Atlantic salmon is also high in cancer-causing toxins like dioxins and PCBs.

(More on the health benefits of eating fish and sustainable fisheries [PDF])

So how can these complex tips be simpler?

Environmental Defense's Seafood Selector provides a list of best and worst choices for the ocean. It highlights fish that are heart-healthy (high in omega-3s) and those that are either high or low in contaminants. It includes advice on how many times it is safe to eat a particular fish each month.

Stay tuned for upcoming posts where I'll focus on the environmental and health aspects of specific seafood choices.