Old McSalmon Had a Farm

As the world hungers for more fish—as a source of protein and heart-healthy omega-3 fats—fish farming (aquaculture) has become a $70 billion a year industry. Whether this is a solution to our dwindling wild fish stocks remains to be seen. But in the meantime, chances are good that your last fish meal came from a “farm” rather than the deep blue sea. Nearly half of the seafood we eat today is, in fact, farm-raised. And much comes from other countries, such as China and Chile. All this raises questions about the health and environmental impact of the fish you eat.

Which fish are likely to be farmed?

Most salmon is farmed, and “Atlantic salmon” is always farmed, since there’s no wild Atlantic salmon left to catch (in contrast, all Alaskan salmon is wild). Two Pacific salmon species—coho (silver) and chinook (king)—are wild-caught as well as farmed. Most shrimp is farmed, as are many mollusks (such as oysters and mussels). Catfish, tilapia, and trout are among the most commonly farmed fish in the U.S.

Do farmed fish have as much omega-3 fats as wild fish?

Fatty fish are the best sources of omega-3s, and farmed fish have about the same levels of omega-3s per ounce as their wild-caught counterparts. But because farmed fish typically eat a high-fat diet and swim less than wild fish, they tend to have more fat overall. Much, though, depends on the specific fish chow—and that varies considerably. In general, farmed fish fed more fishmeal and fish oil (from wild-caught fish) have more omega-3s than those fed a more grain-based diet with vegetable oils, an increasingly common practice because it is cheaper and saves wild fish.

Does farmed salmon have more contaminants than wild?

Like wild salmon, farmed salmon is low in mercury. But studies a few years ago found higher levels of potentially harmful PCBs and other industrial pollutants in farmed salmon (particularly from Europe), which was blamed on the feed. When anchovies, sardines, and other small oily fish are made into fishmeal, the trace amounts of contaminants in them are concentrated. As a result, farmed salmon are likely to consume more contaminants than wild salmon (which eat a more varied diet)—and they accumulate more fat, where the contaminants are stored. Fish chow has reportedly been improved, but more research is needed to determine if farmed salmon today really has lower contaminant levels. PCBs have been linked to cancer, at least in animals, and other potential health problems. To reduce them, you can remove the skin from farmed salmon and trim any visible fat.

What about contaminants in other fish?

Aquaculture in developing countries, where much of our farmed fish comes from, tends to rely most heavily on antibiotics, pesticides, disinfectants, and other chemicals to control disease and promote growth. The amount of residues left in the fish is largely unknown. Some farmed fish from overseas has been found to contain banned substances—and thus is not allowed into the U.S.—but the FDA tests only a fraction of imports and does not test for all contaminants. While routine exposure to some of these chemicals can pose a risk to workers at fish farms, the health effects in people who eat the fish are not known.

What makes farmed salmon orange?

The color comes mostly from astaxanthin, a carotenoid pigment added to fish feed. Without it, farmed salmon would be gray. Astaxanthin has antioxidant properties and possible health benefits. The pigment accumulates in wild salmon when they eat krill and other sea creatures that feed on astaxanthin-rich algae. Astaxanthin in fish feed is almost always synthetic, which is cheaper but may not have the same potential benefits in the body.

Is it true that the fat in farmed tilapia is harmful?

No. A recent study from Wake Forest University in North Carolina that got a lot of press found that farmed tilapia and catfish have low levels of omega-3 fats but relatively high levels of omega-6s (another group of polyunsaturated fats). The authors theorized that this combination could increase inflammation in people with heart disease and other inflammatory-related conditions, because certain omega-6s promote inflammation, while omega-3s dampen it. But the concept that a high ratio of omega-6 to omega-3 fats promotes disease is controversial and unproven. And tilapia and catfish are not even fatty fish to begin with—though they are good sources of protein and other nutrients. The best advice is to get more omega-3s from fatty fish such as sardines, mackerel, herring, salmon, and trout, and not worry about the ratio.

Is fish farming bad for the environment?

Depending on the location, type of fish, and other variables, it often is. For example, the creation of shrimp farms in tropical Asia destroys the mangrove forests that prevent coastline erosion and serve as nurseries for baby fish. Shrimp and salmon farming, in particular, are cited for polluting the water with vast amounts of fish excrement and uneaten feed containing antibiotics and other drugs (used to offset disease due to overcrowding in pens). And salmon routinely escape their net pens into the open ocean, where they can spread disease and interbreed with native species, with unknown consequences. On the other hand, when done responsibly, aquaculture can help ease pressure on wild fish populations (threatened largely by overfishing) and provide a more sustainable—and cheaper—source of seafood. And farming fish is more energy-efficient than raising cattle and other land-based animals.

Is there such a thing as organic farmed fish?

The USDA has yet to set organic standards for farmed fish. (Wild fish can never be called organic, since there is no way to control what they eat.) Some stores and restaurants sell “organic” farmed fish, based on standards used by other countries or independent certifiers, but these are not uniform, may be lax, and are difficult to verify. Some major retailers, including Whole Foods, Wal-Mart, and Wegmans, have established their own standards for farmed seafood in collaboration with environmental groups and/or the aquaculture industry, many of which are similar to those used in organic food production, though the seafood is not labeled as organic.

How can you know for sure if your fish is farmed or wild?

You can’t always. New “country of origin labeling” (COOL) requires that supermarkets—but not restaurants or, strangely enough, fish markets—disclose where their fish come from and whether they were farmed or wild-caught, but there is little over-sight. Moreover, while price should be a good indicator (wild counterparts generally cost a lot more), some retailers may mislabel fish to get a higher price. In 2005 the New York Times found that six out of eight salmon samples labeled as wild in high-end Manhattan stores were really farmed. Be especially suspicious of fresh “wild salmon” sold November through March, the off-season (though frozen wild salmon may be available). And don’t be fooled by the new marketing label “ocean-raised”: it may sound like the fish was wild-caught, but this is the same as “farm-raised.” Your best bet for getting high-quality fish is to know your fish seller, who should be able to answer specific questions about the fish and produce a paper trail back to its source.

What about canned and smoked salmon: farmed or wild?

Most canned salmon is wild and says so, though more and more companies, including Kirkland (Costco brand) and Bumble Bee, are now using farmed salmon in some of their products (if it’s labeled “Atlantic” salmon, it’s farmed). If you want wild salmon, look for canned Alaskan pink or sockeye (also called red or blueback) salmon. In contrast, most smoked salmon is farmed.

Bottom line: a good catch

The health benefits of eating two or three weekly servings of fish (a serving being four to six ounces)—whether farmed or wild—outweigh potential risks. Varying your choices and selecting fish lower on the food chain (small fish such as herring, mackerel, and sardines) will reduce your exposure to contaminants. Here are resources that can help you pick fish that are lower in contaminants and are raised or caught in environmentally responsible ways: Environmental Defense Fund, Blue Ocean Institute, and Monterey Bay Aquarium.

UC Berkeley Wellness Letter, November 2008

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