I grew up in Seattle where the arrival of Copper River salmon in grocery stores signaled the start of summer. When it was finally “salmon season,” we would eat salmon weekly (at least). Some of my fondest memories are of those dinners: a large fillet of grilled salmon seasoned with butter and a few simple herbs, a salad, and my mom’s rice pilaf.
Now I live in North Carolina, and it is not as easy to find fresh, affordably priced wild-caught salmon. There are some good frozen options, and wild-caught salmon is available sporadically in late May and June. However, more often than not, grocery stores and restaurants sell and serve farmed salmon.
Back in the early 2000s, many experts recommended avoiding farmed salmon.1 This is because farmed salmon had much higher levels of toxic chemical contaminants and the process of raising farmed farmed salmon caused significant environmental pollution.1,2
What exactly are the differences between farmed and wild-caught salmon? Is farmed salmon a food we should avoid?
Identifying farmed and wild-caught salmon:
In general, Atlantic salmon is farmed and Pacific salmon is wild. At a grocery store, Atlantic (farmed) salmon will be called simply “Atlantic salmon”. Atlantic salmon is pale in color with large white stripes (photo below). Conversely, there are multiple types of predominantly wild-caught Pacific salmon: Chinook (King), Coho (Silver), Sockeye (Red), Keta (Chum), and Pink (Humpback). The taste, color, and nutritional profile of these wild-caught salmon vary widely. Also, at the store or in a restaurant, wild-caught salmon will be labeled simply because it can command a higher price than farmed salmon. Note that some Chinook and Coho salmon is farmed (mostly from New Zealand and Chile), so be sure to read labels if you are looking for wild-caught fish.3
What do wild-caught and farmed salmon eat?
When evaluating foods from animal sources, it is important to understand what they eat. An animal’s health and the nutritional value of eating them is dictated by what they eat. As Michael Pollan wrote in In Defense of Food: An Eaters Manifesto, “You are what you eat eats.”4
Wild-caught salmon are predatory animals that eat primarily smaller fish and krill. Krill are small crustaceans at the bottom of the food chain that feed on phytoplankton.5 As such, krill and the fish that eat them are rich in omega-3 fatty acids (more on those later in this post).
Farmed salmon are kept in enclosed pens and eat whatever they are fed. This is typically pelleted food composed of fish meal, fish oil, processed food by-products (corn, wheat, soy), animal by-products, and ingredients to color their flesh.1,6 Farmed salmon are typically fed fish meal and fish oil from fish higher on the food chain then what wild-caught salmon would typically eat and these sources tend to have higher levels of chemical contaiminants.1 Also, because of their tight living quarters, farmed salmon are prone to disease are frequently fed antibiotics.7
Nutritional differences between farmed and wild-caught salmon:
All salmon is considered a good source of lean protein, with a 4-oz serving providing, on average, 24 grams of protein.8 The 2015-2020 Dietary Guidelines for Americans developed by the US Department of Agriculture (USDA) and US Department of Health and Human Services (HHS) recommends eating two to three 4-oz servings of fish a week.9 A 4-oz serving is about the size of an adult palm.10
1. Fat content in farmed and wild-caught salmon
Farmed Atlantic salmon contains approximately twice as much fat as wild-caught Pacific salmon, with the exception of Chinook salmon.3 This is because farmed fish spend their lives in enclosures that limit their activity, as opposed to wild-caught salmon who can swim many hundreds of miles in their lifetime.1 Farmed Atlantic salmon and chinook salmon also contain almost three times as much saturated fat as the other wild-caught salmon. However, at 3.5 grams of saturated fat per 4-oz serving, this is still significantly lower than the 6.5 grams of saturated fat in a 4-oz hamburger.8 Below is a chart detailing the fat content in a 4-oz serving of salmon.8
2. Fatty acid content in farmed and wild-caught salmon
Omega-3. Salmon is considered an excellent source of omega-3 fatty acids, a class of essential fatty acids we can only obtain from foods we eat. Diets rich in omega-3 fatty acids have been associated with improved health outcomes, though most of the studies evaluating their health benefits are observational.11 The NIH provides a good overview of omega-3 fatty acids and their health benefits.4
Below is a chart of three main omega-3 fatty acids in various types of salmon: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).8 Note: Exact omega-3 fatty acid content of salmon will vary by species, season, and farming conditions.
Farmed salmon and Chinook salmon are exceptionally high in omega-3 fatty acids due to their higher fat content. However, all types of salmon are considered a good source of omega-3 fatty acids. Consuming a 4-oz serving of any of the above salmon types would provide an adult with between 2x to 9x the daily recommended intake of DHA and EPA set by the World Health Organization.12
Omega-6. Omega-6 is another essential fatty acid and is found predominantly in vegetable oils. While there is research indicating that some omega-6 fatty acids are considered pro-inflammatory, the American Heart Association (AHA) conducted a review of the scientific literatures and concluded that “aggregate data from randomized trials, case-control and cohort studies, and long-term animal feeding experiments indicate that the consumption of at least 5% to 10% of energy from omega-6 polyunsaturated fatty acids reduces the risk of CHD relative to lower intakes.”13
Below is a chart of the linoleic acid (a prominent omega-6 fatty acid) in various types of salmon.3 Note: Exact omega-6 fatty acid of salmon will vary by species, season, and farming conditions.
All species of wild-caught salmon have low levels of omega-6 fatty acids, this is because they eat small fish and krill. However, this is not the case with farmed salmon. Because farmed salmon are fed vegetable oils from corn, wheat, soy (and other by-products of our processed food) the omega-6 content in farmed salmon is quite high.14
Does this mean you should avoid farmed salmon because of the elevated omega-6 fatty acid levels? No. Fish are the primary source of omega-3 fatty acids and there is no conclusive scientific evidence indicating that consuming elevated levels of omega-6 fatty acids from fish negatively affects your health.
Other differences between wild-caught and farmed salmon:
1. Chemical contaminants
You may have seen a recommendation that pregnant women or children should limit their consumption of king mackerel, shark, swordfish, and tilefish.15 This recommendation is based on those fish containing high levels of chemical contaminants, like methyl mercury and polychlorinated biphenyls (PCBs). These contaminants were industrial chemicals used from 1929 to 1979, when they were banned. However, they are persistent in the environment (meaning they don’t break down) and are fat soluble, so they build-up in whatever eats them. PCBs and methyl mercury have been shown to cause adverse health effects and some fish are the major dietary source of these contaminants.15 This is because fish that eat high on the food chain (i.e. other fish that are only a little smaller than themselves) are eating other contaminated fish and storing the contaminants in their own fat.
With that said, the Dietary Guidelines for Americans as well as guidelines from the Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) agree that the benefits of eating fish outweigh the potential health risks from chemical contaminants.9,10
How do the contaminant levels in wild-caught and farmed salmon compare?
In 2004, there was a study published in the journal Science that showed that farmed salmon contained higher levels of PCBs, dioxins, and many other persistent chemicals when compared with wild-caught salmon.16 The study also showed that where the fish were farmed had a huge impact on chemical contaminant lives: salmon farmed in Europe contained the highest levels of contaminants compared to those farmed in North and South America. The source of the contamination was attributed to the forage fish (i.e. fish meal and fish oil) fed to the farmed salmon.
Do farmed salmon still contain more chemical contaminants than wild-caught salmon?
It would stand to reason that the shift to predominantly vegetable based ingredients in farmed salmon’s feed should result in a decrease in chemical contaminants. Unfortunately, there isn’t a more recent of contaminants in wild-caught and farmed salmon. In 2013, the USDA added salmon to its annual Pesticide Data Project to analyze the residual pesticide levels of common agricultural pesticides and environmental contaminants.17 However, the analysis pooled both wild-caught and farmed salmon samples (both processed and raw) so the results are essentially meaningless.
How do you know if your salmon is low in chemical contaminants? Buy wild-caught salmon or talk to your grocer. Some supermarket chains (like Whole Foods and Wild Oats) only sell farm-raised salmon from companies who test low for chemical contaminants.18
Another consideration when choosing farmed salmon is whether or not the fish were fed antibiotics. The enclosures where farmed fish are raised are a breeding ground for diseases. This is true for salmon farming where antibiotics are frequently used. When measured, the residual antibiotics levels in farmed salmon are within regulatory limits.7 However, even at low levels, antibiotics can prompt antibiotic resistance.
The use of antibiotics in salmon farming is a concern because of the development of antibiotic resistant bacteria. This is a huge public health concern because there is a direct link between using antibiotics on farms and the development of antimicrobial resistance in humans.19 In the US, four times more antibiotics are used by farm animals than humans.20 Read more about the concerns with using antibiotics in farming and the development of antibiotic resistant bacteria.
How can you purchase salmon that wasn’t raised with antibiotics?
Buy wild-caught salmon or farmed salmon that was raised without antibiotics. Some supermarket chains (Whole Foods) only sell farm raised salmon that was raised without antibiotics while others (Costco) will label the farmed salmon as “raised without antibiotics”. Country of origin can also tell you about whether or not farmed salmon was raised with antibiotics. Almost all farmed salmon raised in Norway is raised without the use of antibiotics while Chile uses an exorbitant amount of antibiotics. In 2015, Norway used 0.17 grams of antibiotics per ton of farmed salmon while Chile used 660 grams antibiotics per ton of fish.21
All salmon is an excellent source of protein packed with omega-3 fatty acids.
1. Wild-caught salmon is a wise choice.
Wild-caught salmon is a wise choice as it is lower in chemical contaminants and free of antibiotic residues.
2. There are good farmed salmon options available.
Purchase farmed salmon from grocers that verify the fish are low in chemical contaminants. Talk to your grocer or fishmonger. Some supermarket chains (like Whole Foods and Wild Oats) only sell farmed salmon from companies who raise fish that test low for chemical contaminants.
Purchase farmed salmon raised without antibiotics. Almost all farmed salmon raised in Norway is without the use of antibiotics.7 When purchasing salmon at the store, there should have basic information on the packaging, or you can ask the fishmonger / butcher at your local grocery store for more information.
Remove salmon skin prior to eating. Removing the skin from salmon before eating is one easy way of reducing exposure to chemical contaminants. In fact, a study by researchers at the University of Toronto showed that removing the skin before eating reduced exposure to contaminants by up to 37%.22 When cooking salmon, cook it in a way that allows the fat to drain off (grill, broil, poach) and remove the fatty (dark) areas prior to eating.21
- What We Eat, Marion Nestle, 2006 (link)
- Why farmed salmon is becoming a viable alternative to wild-caught, Tamar Haspel, The Washington Post (link)
- Seafood Watch App, Monterey Bay Aquarium (link)
- In Defense of Food, Michael Pollan, 2008 (link)
- Krill, Wikipedia Website (link)
- Table of Atlantic Salmon Feed Meal Ingredients, Food and Agriculture Organization of the United Nations Website (link)
- Vaccinating Salmon: How Norway avoids antibiotics in fish farming, World Health Organization Website (link)
- USDA National Nutrient Database for Standard Reference, USDA Website (link)
- Dietary Guidelines for Americans, 2015-2020, Eighth Ed. (link)
- 2017 EPA-FDA Advice on Eating Fish, FDA Website (link)
- Omega-3 Fatty Acids, National Institutes of Health Website (link)
- Interim Summary of Conclusions and Dietary Recommendations on Total Fat & Fatty Acids, 2008, World Health Organization Website (link)
- Omega-6 Fatty Acids and Risk for Cardiovascular Disease, Circulation, 2009, 119: 902-907 (link)
- Survey of n-3 and n-6 polyunsaturated fatty acids in fish and fish products. Lipids in Health and Disease, 2012, 11:144 (link)
- Fish and polychlorinated biphenyls (PCBs), Mayo Clinic Website (link)
- Global Assessment of Organic Contaminants in Farmed Salmon, Science, 303, 226-229 (link)
- USDA PDP 2013, Salmon Special Project (link)
- Quality Standards for Farm Seafood, Jan 2014, Whole Foods Market Website (link)
- The Challenge of Antibiotic Resistance, Stuart Levy, Scientific American, 1998 (link)
- Antibiotic Resistance in Humans and Animals, National Academies of Science Website (link)
- With record antibiotic use, concerns mount that Chile’s salmon farms brewing superbugs, Allison Guy, Oceana Website (link)
- Effects of skin removal on contaminant levels in salmon and trout filets, Science of the Total Environment, 443: 218-225, Jan 2013 (link)