Clean Eating Buyer's Guide to Seafood

Shopping for seafood can be a little tricky. The following guide can help you decipher what to look for in different fish and shellfish so you can choose seafood that is fresh and raised using standards for sustainability that you're looking for.

Seafood is an excellent source of lean protein. And some types of fish, particularly cold-water species like salmon, tuna, sardines and trout, are rich in two important omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Studies show that these omega-3 fats may reduce the risk of heart disease and may also provide other health benefits, such as helping to prevent Alzheimer's disease and boost your mood. But choosing fish means navigating other health and environmental concerns.

One health concern is mercury, but for most people the benefits of eating fish outweigh risk from the methylmercury that's found in varying levels in seafood. In general, the larger (and older) the fish, the higher in mercury it will be (the metal accumulates over time, especially in fish high on the food chain that eat smaller fish). High levels of mercury can cause tingling or numbness in fingers and toes and vision problems, and can affect infant brain development. Even consistent, low-level mercury exposure can leave you fatigued or make concentrating difficult. The USDA's Dietary Guidelines say to eat at least 8 ounces of seafood a week-choosing lower-mercury fish (salmon, shrimp, canned light tuna, tilapia, cod) and some omega-3-rich fish. Follow these guidelines and you should be fine.

So where's the line of "too much"? If you cook up a high-mercury fish (tilefish, shark, swordfish, albacore tuna, king mackerel) even just once a month, some say you might get too much mercury. And a 2016 Environmental Working Group report found that eating tuna steaks, sushi tuna, sea bass, halibut and marlin could also be risky. Still, there's no clear cutoff. Women who are or may become pregnant or are breast-feeding, and young children should avoid high-mercury fish.

Making an eco-friendly choice varies according to the type of fish, where it's from and whether it's wild or farmed. At the fish counter, you should see country-of-origin labeling, now required by federal law. For help making informed choices, and for the most up-to-date information, check the websites of several expert sources, including Monterey Bay Aquarium's Seafood Watch, the Marine Stewardship Council and The Safina Center. Also good to know when fish shopping: most wild-caught fish is frozen at sea, so frozen or previously frozen fish is often the "freshest" you'll find. Fish should look moist and firm and should have a mild smell.

Eat Up: Healthy Fish & Seafood Recipes

How to Shop for Fish and Shellfish:

Catfish

Most catfish on the U.S. market is farmed and, when raised in recirculating systems or in U.S. ponds, is considered a good choice. Pangasius, a farmed catfish imported from Vietnam, Cambodia and China, is popular in Asian restaurants and may also be called basa, swai, tra or sutchi. You may see it frozen or previously frozen at the fish counter. Unless pangasius has a Marine Stewardship Council seal, it likely was raised using intensive pond-farming practices that are environmentally destructive and potentially unhealthy, according to Seafood Watch. In addition, there have been concerns about antibiotic use in foreign catfish farming. However, according to seafoodhealthfacts.org (another helpful source for deciding what fish to buy), practices are improving thanks to consumer demand for eco-friendly fish.

Cod & Pollock

Cod are a versatile white fish and are mostly wild-caught (farming is just being developed for these species) but have problems with many of their fisheries, including overfishing and excess bycatch. Atlantic cod stocks are particularly depleted. Pacific cod or eco-friendly farmed Atlantic cod (in tank-based systems) are the best choices.

Alaskan pollock is the largest U.S. wild fishery. The National Oceanic and Atmospheric Administration says these fisheries are well-managed, but Seafood Watch recommends that you choose products with the Marine Stewardship Council's blue checkmark label.

Salmon

A fatty fish, salmon is especially high in omega-3s and has become a go-to dinner choice for good reason. Most wild salmon is considered a sustainable choice.

Farmed Atlantic salmon is widely available and affordable, and its omega-3 levels are comparable to those of wild salmon. Large and high in fat, this salmon is full-flavored, moist and very versatile for cooking. But many farmed salmon are not considered a sustainable choice, due to farming systems that pollute surrounding waters and threaten wild fish populations. Look for fish raised in land- or tank-based systems, which are better for the environment than most traditional open-net farms. Seek out farmed salmon that have a third-party certification for sustainability, such as the Global Aquaculture Alliance's Best Aquaculture Practices. Look for their logo on packages. There is no regulated organic standard for salmon, so if you do see an "organic" label, it doesn't necessarily mean anything.

Recipe: Grilled Salmon with Tomatoes & Basil

Tilapia

A freshwater fish that originated in North Africa, tilapia can now be found at fish counters across the U.S., where its mild taste and light white meat have made it so popular that it's been nicknamed "aqua chicken."

Since tilapia is an herbivorous fish, tilapia farms don't need to use wild fish for feed, minimizing some of the environmental impact. And tilapia actually help clean the water by eating algae. Look for North American farm-raised tilapia, grown in closed farming systems that limit fish-waste pollution and prevent escapes of the farmed fish into the wild. Some Central and South American tilapia farms used closed systems as well, but tilapia from China and Taiwan may have more negative impacts, because pollution and antibiotic use aren't as well regulated in these countries and the farms are open to surrounding waters.

Tuna

A warm-water fatty fish, tuna is found throughout the world's seas. Yellowfin and bigeye tuna, also called ahi, are common at supermarket fish counters. Yellowfin and skipjack are what you'll usually find canned under the "chunk light" label.

Tuna is high in omega-3s, but can also be high in mercury, since these big fish eat high on the food chain. Those who need to be concerned about mercury (pregnant and breast-feeding women, and growing children) should opt for smaller species-look for yellowfin (ahi) tuna at your seafood counter and choose canned chunk light tuna, rather than white (albacore). Avoid bluefin tuna, used mostly in sushi and sashimi: stocks of these huge fish are severely depleted, and the methods used to catch them endanger other sea creatures, such as sea turtles and sharks.

Recipe: Tuna & Olive Spinach Salad

Clams

Clams are a stellar choice for two reasons: these bivalves are especially high in B vitamins as well as minerals, such as selenium, zinc and magnesium, and they represent one of the few truly environmentally friendly fisheries. Natural stocks are healthy and sufficient to meet demand, farms are well-managed, and clams' active filtering can improve the waters they grow in. Most clams get a "best choice" rating from Seafood Watch.

Check to make sure whole, in-shell clams are alive (shells should be closed or close when you tap them). People at high risk for foodborne illness should avoid eating raw clams. If a recipe calls for chopped clams, look for them fresh or frozen in the seafood department: compared to canned, they have a higher clam-to-liquid ratio and are lower in sodium. Canned baby clams also work well in many recipes.

Crab

Look for crab in the seafood department of large supermarkets. "Jumbo" or "lump" crabmeat is higher quality, with a sweeter taste, more toothsome bite and larger pieces; claw meat is a budget–friendly option. If you live in an area known for crab, you may be able to get live or freshly cooked crabs at the seafood counter of your local market.

Most U.S. crab is considered sustainable, but Seafood Watch advises being wary of crab labeled "Atlantic rock crab" (from New England)-a label that's fine when authentic but that's often used on other types from poorly managed fisheries. Crab from Canada, Australia and Norway is usually a good choice, but other imported crab, often sold canned from Southeast Asia, should be avoided.

Recipe: Muffin-Tin Crab Cakes

Scallops

Sea scallops are larger and are great for sautéing or broiling. Try the smaller bay scallops in soups or tossed in a pasta sauce. Both farmed and wild scallops are a sustainable choice.

We recommend cooking with "dry" sea scallops (scallops that have not been treated with sodium tripolyphosphate, or STP). Scallops that have been treated with STP ("wet" scallops) have been subjected to a chemical bath and are not only often mushy and less flavorful, but also will not brown properly because they'll give off too much liquid. Dry sea scallops are often labeled as such.

Shrimp

Raw, frozen and cooked shrimp are all sold by the number needed to make 1 pound-for example, "21-25 count" or "31-40 count"-and by more generic size names, such as "large" or "extra large." Size names don't always correspond to the actual "count size." To be sure you're getting the size you want, order by the count (or number) per pound.

Shrimp's popularity has led to environmental problems from intense farming and fishing. Both wild-caught and farm-raised shrimp can damage surrounding ecosystems. Fortunately, it is possible to buy shrimp that have been raised or caught with sound environmental practices. Look for shrimp that's certified by an agency like the Marine Stewardship Council. If you can't find it, choose wild-caught shrimp from North America-it's more likely to be sustainably caught.

For best taste and health, limit preservatives that are often used by processors when freezing shrimp. You can see if they've been used by reading the package label. Here are the three to watch out for:

Sodium bisulfite is considered safe by the FDA, though some people are sensitive to it. It's only required to be on the label when it exceeds 10 parts per million.

Sodium tripolyphosphate (STP) bulks up shrimp, causing them to shrink when cooked. It boosts sodium levels by more than four times in some brands. To figure out how heavily treated your shrimp is, check the label and compare it to this baseline: untreated raw shrimp has a sodium count of about 250 mg for every 100 grams.

Everfresh is also used as a preservative to control black spots. It's made of 4-hexylresorcinol, a compound with antiseptic properties (also in throat lozenges). The FDA considers it safe. It doesn't require labeling and is accepted by most organic retailers. But a recent study showed 4-hexylresorcinol can be considered a xenoestrogen, which at high levels may boost estrogen levels, increasing the risk of breast cancer in women.

Recipe: Zucchini Noodles with Avocado Pesto & Shrimp

Watch: How to Make Zucchini Noodles with Avocado Pesto

• Clean-Eating Buyers Guide to Chicken