1. Introduction
2. Lifestyle differences between farmed and wild salmon
3. Toxic contaminant differences between farmed and wild salmon
4. Fatty acid differences between farmed and wild salmon
5. Antibiotic use in farmed salmon
6. Coloring of farmed salmon
7. Lice infestations of farmed and wild salmon populations
8. Genetically modified salmon
9. Conclusion
Introduction
Where are my salmon lovers at?! Regardless of whether you love salmon or abstain from seafood, I think you will find this reading very interesting in regards to the way that farmed salmon are raised, the problems associated with farmed salmon, and the differences between farmed and wild salmon.
Let's start out by highlighting the multiple varieties of salmon. These include Atlantic Salmon, Chinook Salmon, Pink Salmon, Chum Salmon, Coho Salmon, and Sockeye Salmon. To make things simple for this blog, we can classify salmon into two main categories: wild caught salmon and farm-raised salmon. Most of the salmon that is canned or found in the freezer section of your grocery store is generally Pink Salmon according to my experience unless otherwise noted on the packaging. Let's get into the differences between wild caught and farm raised salmon.
Lifestyle differences between farmed and wild salmon
Pink Salmon are the most abundant Pacific salmon and also the smallest, weighing from 3.5 to 5 lbs a piece with a length of 20-25 inches. Pink Salmon hatch in freshwater streams and then migrate to saltwater oceans for feeding. After feeding for about a year and a half, they return to fresh water, spawn (reproduce), and die (3).
The majority of the diet for Pink Salmon is small crustaceans, zooplankton (small aquatic animals), squid, and small fish. Sockeye salmon feed on several of these same animals as well as amphipods (shrimp like crustaceans, and insects (3).
Over half of the salmon currently produced is farm raised (1). Today, most farm raised salmon is produced in Norway, Chile, Scotland, and North America (2).
This may be evident, but Farmed Atlantic Salmon (Salmo salar) are generally contained in large netted areas within the water for obvious reasons. As a result of their containment, the salmon are not able to migrate as some salmon species do and they are not able to feed on the crustaceans, zooplankton, and small fish that wild salmon feed on. By confining farmed salmon, limiting their natural activity, and severely altering their natural diet, we see many stark differences between farm raised and wild caught salmon including toxic contaminant levels, fatty acid differences of the meat, antibiotic use, lice infestations, color additives, and genetic modification which we will dive into below.
Toxic contaminant differences between farmed and wild salmon
Farm raised salmon are not able to receive all of their food from the natural environment. As a result, they must be fed. It is interesting to note that the feed used for the farmed salmon is believed to be the major source of toxic contaminants in these fish, specifically organochlorine contaminants (1). Let's first take a look at where some of these chemicals came from.
Polychlorine biphenyls (PCBs) are a type of organochlorine that were initially designed to be resistant to high temperatures and pressures. They were widely used in capacitors, transformers, hydraulic fluids, lubricants, and plasticizers until their end of commercial production in 1977 due to health effects associated with exposure. In 1979, the United States Environmental Protection Agency banned the use of PCBs (11). Despite their ban, PCBs have been leaked int the environment through spills and improper storage and disposal. Once in the environment, the PCBs strongly bind to soil or sediment throughout the world and are ingested by marine life like fish.
When comparing farm raised Atlantic salmon and wild caught Pacific salmon, farm-raised salmon contains higher concentrations of dioxins, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers, and some pesticides, many of which are carcinogenic or cancer causing (1).
A 2004 study looked at the organochlorine contaminants in roughly 700 different farm and wild salmon from around the world to compare levels of contaminants in the fish. They measured the concentrations of 14 organochlorine contaminants including PCBs, dioxins, toxaphene, and dieldrin. Thirteen of the 14 contaminants were significantly greater in the farmed salmon than the wild salmon. Furthermore, salmon from Europe are more significantly contaminated than those farm-raised in in North and South America (5).
What's the significance of these organochlorine contaminants? Let's take a look at the PCBs that we mentioned earlier. These are a group of chemicals that are resistant to being metabolized by animals, meaning we can't break them down very well. The result is that they become deposited in the fatty tissues of humans and animals when ingested. The toxic effects from may include harm to the skin and immune system, negatively impact the reproduction, development, and endocrine function, and contribute to the development of cancers (10). Birth defects and slower mental development may also be linked between PCB exposure in mothers (11).
Fatty acid differences between farmed and wild salmon
The pressure for producing a greater amount of farmed seafood has been steadily rising. Over the past 2 decades, the annual global production of farm raised salmon has increased from about 60 million lbs to 2.9 billion lbs! (1). With the pressures of an increased demand, the feed supply for farmed salmon also changed. Initially, farmed salmon were fed a diet consisting of marine ingredients, including fish oil and fish meal that came from fisheries (2). This became less sustainable and we began resorting to terrestrial (land) based sources of feeds like plants and seed oils.
Salmon in the wild are able to feed on other fish and other marine sources as we mentioned a few sections earlier. As the food source of farmed salmon shifted towards land based products, the nutritional quality of the fish has changed as well. The land based feed sources include plants, seed oils, or vegetable oils. In Europe, rapeseed oil is the most commonly used oil alternative in salmon feed due to the low cost and availability. Unfortunately, rapeseed oil and many other vegetable oils contain a high concentration of omega-6 fatty acids but lack the beneficial omega-3 fatty acids like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) (2).
Between 2010 and 2015, the percentages of land based fatty acids (oleic, linoleic, and alpha-linoleic acids from plant oils) doubled in farm raised fish while the marine based oils (EPA and DHA) decreased by about half (2)! The levels of EPA and DHA in farmed Scottish Atlantic salmon have decreased from 2.74 g to 1.36 g per 100g between 2006 and 2015. That means the levels of your healthy, beneficial fatty acids have decreased by about half in only the span of 9 years due to what salmon are being fed in farmed operations (2).
It is true that farmed Atlantic salmon have over twice the amount of fatty acids compared to Wild Pacific Salmon. However, they also have roughly six times the amount of omega-6 fatty acids (that promote inflammation) with only 3 times as much omega-3 fatty acids (that are anti-inflammatory). The reason for this discrepancy is likely due to the feed given to the farm raised salmon from corn and soy which are high in omega-6 fatty acids (1). Remember, the ratio of beneficial omega-3 fatty acids to inflammatory omega-6 fatty acids is critical in determining how beneficial the salmon is for your health, and farmed salmon has a higher ratio of omega 6:3. See the grass fed vs. conventional beef blog to learn more about omega-6:3 ratio!
Random fact: Engineers and scientists are developing genetically modified oilseed crops that create healthy omega-3 fatty acids like EPA and DHA. They do this by inserting genes from microalgae that code for enzymes that produce these fatty acids into the crops. The result is that the crops yield seeds that have up to 20% of their fatty acid content coming from omega-3 fatty acids. Additionally, a genetically modified yeast strain that produces omega-3 fatty acids is currently being used with Chilean salmon (2).
Antibiotic Use in Farm-Raised Salmon
Similar to the poultry industry where antibiotics are used to keep bacterial disease at bay when large quantities of chickens are living in close quarters, antibiotics have been part of the farm-raised salmon story. Large amounts of antibiotics including drug families like the quniolones and tetracyclines have been used in the prevention of bacterial disease spread in salmon populations. A major reason for the use of these antibiotics is due to the unsanitary conditions that the fish are living in. Despite the use of antibiotics, viral and parasitic infections are still able to exist in unsanitary conditions, potentially contributing to antibiotic resistance within farm raised salmon populations (8).
Furthermore, when fish are fed antibiotics, they are not immediately eliminated from the fish. One study examined pacific salmon that were fed diets containing tetracyclines. These tetracyclines were shown to be permanently deposited in the salmon skeletons and were also detectable after periods of rapid growth (9).
Coloring of Farm-Raised Salmon
How would you like to cut into a nice juicy, gray salmon fillet? You probably wouldn't. But that's exactly what farm raised salmon would look like if they didn't put ingredients into their food to help color the flesh. Carotenoids are a large group of pigments found in plants and animals. One particular carotenoid called astaxanthin is responsible for the pink-red color observed in the flesh of wild salmon. Astaxanthin makes up greater than 90% of the total carotenoids found in wild salmon.
Astaxanthin cannot be made by salmon, it must be consumed through diet (6). Wild salmon are able to eat crustaceans that contain astaxanthin, absorb it into their blood stream, and deposit it in the muscles and skin. Because farm raised fish are not able to eat seafood containing astaxanthin, but are at the mercy of what is thrown into their confined waters, their flesh do not naturally have the normal pink-red color that wild salmon have. To make the salmon more desirable to the consumer, astaxanthin is supplemented in the feeds of farm raised salmon in order to give it the pink-red appearance that customers are used to (6).
The role of astaxanthin extends beyond giving a desirable appearance to the salmon. It is a potent antioxidant that may play a role in reproduction, metabolism, growth, and health of the salmon as well (6,7). Astaxanthin is also thought to play a role in protecting the fatty acids found in salmon from becoming oxidized or 'rancid'. Lastly, it is shown to be 100 times more potent of an antioxidant than Vitamin E! (6).
Lice infestations of farmed and wild salmon populations
The salmon louse, Lepophtherius salmonis, are a parasite that have naturally effected wild salmon populations. The first documentation of salmon lice may extend as far back as 1750 (12). Although the salmon lice are a natural species, salmon farms, where a high concentration of salmon are in a confined area, amplify the potential for parasitic infections from salmon lice. Not only are salmon lice a threat to farmed salmon, there is thought that the amount of salmon lice from the farmed areas contributes to a rise in salmon lice infections in the wild populations that share the same waters. Salmon lice negatively impact both wild and farmed salmon by attaching to the surface of the salmon and feed on the host, leading to erosion of the skin as well as stressing the fish. I (12).
Not only do the heavy infestations of salmon lice potentially cause infestations of the wild salmon populations, the farmed salmon need to be treated for these parasitic infections. Initially, formaldehyde baths were used which were questioned in terms of safety. Oral organophosphates were introduced through feed but the safety of these was questioned as well. Eventually, a bath treatment drug called dichlorvos became the treatment of choice up until the early 1990s. At this time, resistance was becoming an issue. Alternative therapies were attempted including hydrogen peroxide treatments and ivermectin (12). In 1999, a drug called enamectin benzoate was released that was not only more effective, but it had a better safety profile as well. As of 2013, this remains the treatment of choice (12).
Genetically modified salmon
In 2015, a genetically engineered salmon called the AquaAdvantage Salmon was brought to the public eye for FDA approval. These salmon are genetically engineered to grow faster than non-genetically modified farm-raised salmon. A segment of Chinook salmon DNA that coded for the growth hormone gene was inserted into the fish along with a sequence of DNA from an ocean pout fish that turns on this growth hormone gene (this is called a 'promoter'). Essentially what this means is that the genetically modified salmon have their growth hormone gene turned on more than a normal salmon, allowing them to grow larger, faster due to the genetic modification (4).
The FDA approval was contingent upon restricting the raising of these genetically modified salmon in ocean net pens, which is the method that most farmed salmon are raised. The genetically modified salon must be raised in contained land-based facilities which are currently in Canada and Panama in order to prevent the salmon from escaping into the wild and impacting the environment (4).
In 2016, the FDA issued an import alert (Import Alert 99-40) on behalf of the 2016 Omnibus Appropriations Act which prevented the importation of genetically engineered salmon into the market until guidelines were established for labeling of the salmon. The big question was whether or not the salmon had to be labeled as genetically modified or not. In December of 2018, the National Bioengineered Food Disclosure Standard Law was enacted by Congress that makes it mandatory to disclose bioengineered food on the labeling. After passing the law on labeling, the Import Alert 99-40 was deactivated and importation of the AquaAdvantage genetically engineered salmon became commercially available in the United States (4).
The next time that you are in the seafood section of the grocery store, look at some of the prepackaged seafood options like sushi or imitation crab meat. You will likely be able to find something along the lines of "produced with genetic engineering" on the packaging of certain products.
Recommendations
When possible, opt for wild-caught salmon opposed to farm raised salmon. If buying frozen salmon, on the back of the package usually you will see the words "wild-caught" or "farm raised" in small font. On canned salmon, you should be able to find the same information. For fresh salmon out of the case at your local grocery store, generally they have the words "wild caught" or "farm raised" underneath the name of the fish. Although wild caught is generally more expensive than farm raised salmon, I recommend always purchasing wild caught when given the option. Aldi grocery stores on the east coast generally carry frozen wild caught Pink Salmon fillets for less than $4 per pound. Wild caught canned salmon generally runs a little bit cheaper than that. Alaskan Wild Caught Sockeye salmon is probably the highest quality fillet on the market.
Conclusion
There are a variety of wild salmon species, with pink salmon being the most abundant Pacific Salmon type (3). Due to the high demand for salmon, over half of the salmon on the market is farm raised (1). Farmed salmon experience a different environment, diet, amount of exposure to infections, and medication exposure that wild salmon. One result of the feed source given to farmed salmon is that they have significantly increased concentrations of toxic compounds, mainly organochlorine contaminants like polychlorine biphenyls (PCBs) when compared to wild salmon (5). Many of these organochlorine contaminants are associated with impairment to the immune, reproductive and endocrine systems as well as cancer (10). The feed that farmed salmon receive also impacts the levels of fatty acids found in the fish. The diets of farmed salmon consists of land based foods like plants and seed oils, rather than fish and aquatic organisms in the wild. The result is an increased concentration of inflammatory omega-6 fatty acids and a decrease of the beneficial omega-3 fatty acids, diminishing the health benefits of salmon (2). Because farmed salmon are raised in confined and sometimes unsanitary areas, treatment with antibiotics to keep bacterial disease at bay is implemented (8). Additionally, antibiotic residue has been found in the skeletons of treated fish (9). Because farm raised salmon are not able to eat their natural diet that is high in a carotenoid called astaxanthin, their flesh is actually gray in color. Obviously this is undesirable to the consumer, therefore their feed is supplemented with astaxanthin to produce the pink-red salmon color (6). When farmed salmon are confined, this creates a breeding ground for parasitic infection, specifically salmon lice (12). As a result, salmon have historically been treated in medicated baths or through their feed to help decrease infections (12). Lastly, genetically engineered salmon called AquaAdvantage Salmon have been approved by the FDA and can be found in grocery stores across America as of December of 2018. This approval was contingent upon the fact that the labeling must specify the genetically engineered nature of the salmon. Salmon is a delicious fish, however due to the toxic contaminants, unfavorable fatty acid profile, unnatural diet and environment, and increased use of medications and antibiotics to counter infection, I believe that it would be a wiser, healthier, and more natural option to purchase and consume wild-caught salmon over farm-raised salmon when possible.
1. Foran, Jeffery A. et al. 2005. Quantitative analysis of the Benefits and Risks of Consuming Farmed and Wild Salmon. The Journal of Nutrition. 135(11): 2639-2643.
2. Sprague, M et al. 2016. Impact of sustainable feeds on omega-3 long-chain fatty acid levels in farmed Atlantic salmon. Scientific Reports. 6: 21892.
3. NOAA Fisheries. Species Directory. Retrieved May 15, 2019. From: https://www.fisheries.noaa.gov/species/farmed-atlantic-salmon
4. Food and Drug Administration. AquaAdvantage Salmon Fact Sheet. Retrieved May 15, 2019. From: https://www.fda.gov/animal-veterinary/animals-intentional-genomic-alterations/aquadvantage-salmon-fact-sheet
5. Hites, Ronald A et al. 2004. Global Assessment of Organic Contamininants in Farmed Salmon. Science. 303: 226-229.
6. Anderson, Stewart. 2001. Salmon Color and the Consumer. IIFET.
7. Bell, J. Gordon et al. 2000. Depletion of a-Tocopherol and Astaxanthin in Atlantic Salmon (Salmo salar) Affects Autoxidative Defense and Fatty Acid Metabolism. The Journal of Nutrition. 130(7): 1800-1808.
8. Millanao, B.A. et al. 2011. Injudicious and excessive use of antibiotics: public health and salmon aquaculture in Chile. Revista Medica de Chile. 139(1): 107-118.
9. Weber, Douglas and Ridgway, George J. 1967. Marking Pacific Salmon with Tetracycline Antibiotics. Journal of the Fisheries Research Board of Canada. 24(4): 849-865.
10. Van den Berg, Martin et al. 1998. Toxic Equivalency Factors (TEFs) for PCBs, PCDDs, PCDFs for Humans and Wildlife. Environmental Health Perspectives. 106(12): 775- 792.
11. Illinois Department of Public Health. 2009. Environmental Health Fact Sheet Polychlorinated Biphenyls (PCBs). Retrieved: May 16, 2019. From: http://www.idph.state.il.us/envhealth/factsheets/polychlorinatedbiphenyls.htm
12. O Torrissen et al. 2013. Sea lice on wild and farmed salmon. Journal of Fish Diseases. 36: 171-194.
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