Eating fish and shellfish is good for your health - they are lean, low-calorie source of protein that also contain other essential nutrients and omega-3 fatty acids that are especially important for hearth health. The American Hearth Association recommends eating fish at least twice a week. Yet there are several factors that make choosing the right fish difficult for the consumer. High mercury content being one, environmental impact being the other.

EPA and The Food and Drug Administration warn that pregnant women, nursing mothers, women who might become pregnant, and children should not eat swordfish, shark, tilefish, and king mackerel because of their high methylmercury content. The FDA also warns women and children to limit their consumption of tuna. To find out whether you're eating safe, use the calculator at Got Mercury?. Natural Resource Defense Council also offers a guide for fish eating based on the mercury content and environmental impact using data from the FDA and EPA. If no lists are available, it is good to remember that levels of environmental contaminants are generally highest in older, larger, predatory fish and marine mammals while smaller, younger fish have much lower levels, tilapia, trout and anchovy being good examples of those. If no healthy fish are available in your area, opt for purified fish oil as a source of omega-3 fats.

The other big concern with seafood is its sustainability. Many breeds are overfished and becoming endangered and the catching methods are harming the environment. Choosing seafood wisely helps shift demand away from overfished and poorly managed fish and shellfish. Farmed fish (like catfish and tilapia raised in closed systems) can be a better choice at times, while other farmed species like Atlantic salmon can be more problematic. In a non-sustainable aquafarm fish are fattier because they are kept on a diet of corn, soy and ground-up fish, yet have lower levels of omega-3 fats than wild fish, they are doused with antibiotics and exposed to more pesticides. Aquafarming raises many environmental concerns, they are often a threat to the wild species around them and not just because of the waste they create. For example a David Suzuki Foundation has a downloadable summary of a 2007 study about fish farms driving wild salmon toward local extinction by spreading sea lice.

Shrimp is another staple that should be consumed in moderation. For each pound of shrimp caught, 4 to 10 pounds of unwanted marine life - bycatch (including sea turtles) are caught; most of which are discarded and die. Shrimp trawls also impact bottom habitat negatively. Many shrimp farms destroy natural habitat and create disease and pollution problems. Best alternative to trawl caught and farmed shrimp is shrimp that has been caught using traps that are less-damaging. Such traps are being used e.g. in Alaska, California and Maine. So the best advice is to avoid farmed shrimp and salmon, unless organically farmed and caught with traps. CleanFish has a list of trusted brands and companies who farm and catch their seafood with sustainable practices.

Another way of making sure the fish under consideration is sustainable is to look for Marine Stewardship Council's ecolabel. Their website also offers many sustainable fish recipes. When buying seafood, you should also ask the seller/waiter where the food comes from and make your purchasing decisions based on that. Monterey Bay Aquarium has a downloadable pocket guide that is helpful in choosing ocean-friendly seafood in different US regions. Blue Ocean Institute also has a service called FishPhone that gives you access to sustainable seafood information via cell phone. FishOnline has a simple search tool that provides you with information about any fish, including its scientific name, method of production, biology, rating and advice for eating.