Know your Scottish Salmon

Krilling off omega-3s?

Aceite de krill © Com Salud

Scientists noted many years ago that Inuit peoples of the Far North appeared to have lower rates of heart disease; whilst there’s some dispute around early evidence for this, initial findings were attributed to a marine based diet and resulted in much research and interest in supplementation with omega-3s or high fish diets[1].

Omega-3s are fatty acids that our bodies can’t manufacture.  Both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in fish, and α-linolenic acid (ALA) is found in plant food, such as walnuts.

We started off encouraging everyone just to eat more fish, but fast-forward and the plastic-wrapped omega-3 supplement industry, is worth 33 billion dollars annually, and is forecast to grow to 57 billion dollars by 2025[2].  Another omega-3 supplement market, krill oil, is expected to grow to over 800 million dollars by 2023, fuelled by a growing awareness of supposed health benefits in Asia[3].


This is worrying given krill are a major dietary source for penguins and whales, and in the Antarctic are a keystone species. If we over-fish them then it could have significant consequences higher up the food chain.  Whilst there is some positive news from krill fisheries’ agreements to extend Marine Protected Areas (MPAs) in the Antarctic, this species is also at risk from climate change and ocean acidification, so MPAs may not be enough to protect them[4].

Are omega-3s a ‘wonder’ supplement?

Where is the evidence? From a heart health point of view, it seems they aren’t all they’re hyped up to be.

In July, a Cochrane systematic review[5] (gold standard evidence), reported, “There is evidence that taking omega‐3 capsules does not reduce heart disease, stroke or death. There is little evidence of effects of eating fish. Although EPA and DHA reduce triglycerides, supplementary omega‐3 fats are probably not useful for preventing or treating heart and circulatory diseases. However, increasing plant‐based ALA may be slightly protective for some heart and circulatory diseases.”

The review found no real difference between those studies that were of supplement intake vs those with dietary fish but unfortunately there were few studies just with dietary fish.

There are lots of other supposed benefits of omega-3 s, in addition to “and maintain healthy heart function[6]” they are also claimed to “support normal and healthy brain function[7]”, but plenty of systematic reviews show little or no effect: for example, for dementia treatment[8], for progression of macular degeneration[9], for inflammatory bowel disease[10], for cancer[11] and for cognition[12].  Evidence reviewed in 2016 by the Royal College of Obstetricians and Gynaecologists indicates no supportive evidence for omega-3 supplements for maternal or paediatric outcomes. They may have a role in preventing allergy, but results weren’t high enough quality to alter guidance[13]. Further studies may be needed to determine effect on depression and autism, and perhaps other health issues too[14] [15].

So, aside from reaching for the walnuts, what does it mean?  It seems you can’t just capture something from a diet, pop a pill and get an effect.  Though fish consumption diet advice hasn’t changed, the Cochrane review suggests it’s not worth buying omega-3 supplements for heart health. Longer term studies on dietary fish consumption would be welcome since this study didn’t have enough power to show whether a high fish diet had an effect on heart health.

Where does this leave omega-3s in salmon farming?

Around 30 -40% of farmed salmon diet comes from fishmeal and fish oils[16] .  A proportion of this is from krill, which 2017 figures indicate constitute 5% of refined fish oil production

Figures vary widely for fish feed content of fish oil and fishmeal, and estimates for the weight of wild caught fish needed to produce 1 kg of farmed salmon range from 1.68 – 4.9 kg[20].  Recent (2015) figures from The Marine Ingredients Organisation (IFFO) suggest that in some cases this could be down to 0.82 kg of wild fish to produce 1 kg of farmed salmon[21]. Whilst there’s been a reduction in the use of fish meal and fish oils in feed for farmed salmon, it’s still a good source of omega-3.  Unfortunately, one of the reasons that producers aren’t moving to even lower levels of wild fish oils and wild fish in feeds, is that retailers perceive a high demand for omega-3 enriched fish from consumers, who may view it as having additional health benefits.   Will this heart health research, along with consumer concern about krill fishing and wild fish depletion encourage retailers to remove this extra demand from producers?  Whatever happens there, we need to keep supporting innovation to derive maximal nutrition from aquaculture, but without compromising the environment.

Gentoo penguins with krill stained guano © Recliner

Interestingly, a feeding trial begins shortly between University of Stirling and Rothamsted Research in which salmon will receive an alternative source of omega-3 from genetically modified (GM) Camelina oilseed plants[22].  Success of the trial won’t mean these salmon will be on sale in the UK though, due to present retailer policy and consumer concern re GM.

This tipping point between individual marginal health gains and environmental harm isn’t going to go away.  Omega-3s, dietary fish advice and use of GM are just a fraction of the issues that challenge the interface between health and the environment. There are many, many other issues that need addressed, not least prescribing of drugs that are then excreted into the environment[23].  It’s time for environmental stewardship to pervade our approach to 21st century medicine.




[1] Bjerregaard P, Young TK, HEgele RA.  Low incidence of cardiovascular disease among the Inuit–what is the evidence? Atherosclerosis. 2003 166(2):351-7

[2] accessed 6/8/18

[3] accessed 7/8/18

[4] Klein ES, Hill SL, Hinke JT, Phillips T, Watters GM (2018) Impacts of rising sea temperature on krill increase risks for predators in the Scotia Sea. PLoS ONE 13(1): e0191011

[5] Abdelhamid  AS, Brown  TJ, Brainard  JS, Biswas  P, Thorpe  GC, Moore  HJ, Deane  KHO, AlAbdulghafoor  FK, Summerbell  CD, Worthington  HV, Song  F, Hooper  L. (2018) Omega‐3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2018, Issue 7

[6] Boots Pharmaceuticals Max Strength Omega 3 Fish Oil 1300 mg – 60 Capsules.

[7] Haliborange Teensense Omega-3 – 30 Orange Chewable Fruit Burst Capsules.

[8] Burckhardt M, Herke M, Wustmann T, Watzke S, Langer G, Fink A.(2016) Omega-3 fatty acids for the treatment of dementia. Cochrane Database of Systematic Reviews 2016, Issue 4

[9]Lawrenson JG, Evans JR.(2015) Omega 3 fatty acids for preventing or slowing the progression of age-related macular degeneration. Cochrane Database of Systematic Reviews 2015, Issue 4

[10]Lev-Tzion R, Griffiths A, Leder O, Turner D. (2014) Omega 3 fatty acids (fish oil) for maintenance of remission in Crohn’s disease. Cochrane Database of Systematic Reviews 2014, Issue 2

[11] MacLean CH, Newberry S J, Mojica W A, Khanna P, Issa A M, Suttorp M J, Lim Y W, Traina S B, Hilton L, Garland R, Morton S C. (2006) Effect of omega-3 fatty acids on cancer risk: a systematic review. JAMA The Journal of the American Medical Association, 295(4), 403-15.

[12] Cooper RE, Tye C, Kuntsi J, Vassos E, Asherson P  (2015) Omega-3 polyunsaturated fatty acid supplementation and cognition: A systematic review and meta-analysis.  J Psychopharmacol, 29(7), 753-63.


[14] Appleton KM, Sallis HM, Perry R, Ness AR, Churchill R. (2015) Omega-3 fatty acids for depression in adults. Cochrane Database of Systematic Reviews 2015, Issue 11

[15] James S, Montgomery P, Williams K. (2011) Omega-3 fatty acids supplementation for autism spectrum disorders (ASD). Cochrane Database of Systematic Reviews 2011, Issue 11

[16] Shepherd CJ, Monroig Ó, Tocher DR (2017) Future availability of raw materials for salmon feeds and supply chain implications: The case of Scottish farmed salmon. Aquaculture, 467, 49-62.

[17] 2017 Annual Report GOED, 15pp.


[19] Hill S, Atkinson A, Darby c, Krafft BA, Godø OR, Skaret G, Trathan PN, Watkins JL (2016) Is current management of the Antarctic krill fishery in the Atlantic sector of the Southern Ocean precautionary? CCAMLR Science, 23, 31-51.

[20] MCSUK Farmed Fish Information Sheet



[23] Johnson AC, Dumont E, Williams RJ, Oldenkamp R, Cisowska I, Sumpter JP (2013) Do concentrations of Ethinylestradiol, Estradiol, and Diclofenac in European Rivers Exceed Proposed EU Environmental Quality Standards? Environmental Science & Technology, 47(21), 12297-304.