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 However, is this still the case? Should we avoid eating farmed salmon? And what are the differences between farmed and wild salmon?
Identifying farmed and wild salmon:
In general, Atlantic salmon is farmed and Pacific salmon is wild-caught. Farmed salmon is typically labeled “Atlantic” salmon, is pale in color, and has 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 salmon will be labeled simply because it can be sold for a higher price than farmed salmon.
Note: 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 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 from 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 contaminants.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 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
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
Fatty acid content in farmed and wild salmon
Omega-3 content in wild and farmed salmon
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 the health benefits of omega-3 fatty acids 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 content in wild and farmed salmon
Omega-6 is another essential fatty acid 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 wild salmon eat small fish and krill. However, this is not the case with farmed salmon. The high omega-6 content in farmed salmon is due to the salmon feed containing vegetable oils from corn, wheat, soy, and other by-products of our processed food.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.
Chemical contaminants in wild and farmed fish
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
Is there a difference in contaminant levels between wild and farmed salmon?
In 2004, a study published in the journal Science 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 the farm location had a huge impact on chemical contamination of salmon. Salmon farmed in Europe had the highest levels of contaminants compared to salmon farmed in North and South America. The source of the contamination is 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 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, a more recent analysis of contaminants in wild and farmed salmon is not available. 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 (such as Whole Foods) only sell farm-raised salmon that tests low for chemical contaminants.18
Antibiotic use in farmed salmon
Another consideration when choosing farmed salmon is whether or not the fish were fed antibiotics. Farmed fish are raised in crowded enclosures. These tight spaces are a breeding ground for diseases, resulting in the frequent use of antibiotics and other medicines. When measured, the residual antibiotics levels in farmed salmon are within regulatory limits.7 However, the health impacts of chronic, low-level exposure to antibiotics and other medicines, have not been evaluated.
The use of antibiotics in salmon farming is especially concerning because of the development of antibiotic resistant bacteria. According to the U.S. National Academy of Medicine, “there is a direct link between antibiotic use on farms and the spread of antibiotic resistant bacteria to human populations.”19,20 In the United States, farm animals consume four times more antibiotics than people. Read more about the concerns with using antibiotics in farming and the development of antibiotic resistant bacteria.
Purchase salmon raised without antibiotics
Buy wild-caught salmon or farmed salmon raised without antibiotics. Some supermarket chains, such as Whole Foods Market, only sell farmed salmon raised without antibiotics. Other stores, such as 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. Chile, on the other hand, 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
Conclusions about farmed and wild salmon
All salmon is an excellent source of protein and is packed with omega-3 fatty acids. By law, all salmon must be labeled with its country or origin and whether it was farmed or caught wild.
Wild salmon is a wise choice
Wild-caught salmon is lower in chemical contaminants and free of antibiotic residues. If fresh wild salmon is out of season or prohibitively expensive, look to purchase frozen wild salmon. However, it is important to still check the ingredients of frozen wild salmon! Some suppliers add preservatives or other additives ahead of freezing the wild salmon to “retain moisture.”
There are a few good options for farmed salmon
Purchase farmed salmon raised without antibiotics
Most farmed salmon is fed antibiotics and other medicines because of tight living conditions. Therefore, it is necessary to look specifically for farmed salmon with a label that specifically states “raised without antibiotics”. If the label is not clear, ask the fishmonger / butcher at your grocery store for more information.
Note: Almost all farmed salmon from Norway is raised without antibiotics.7
Which grocery stores sell healthier farmed salmon? Click here for our free guide summarizing which major retailers sell healthier farmed salmon.
Remove salmon skin prior to eating to reduce exposure to chemical contaminants
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
Pin article for later:
- 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)