Farmed Salmon: Evolving Thoughts

This post is about research I’ve done into eating salmon as well as some notes on food choices specific to Singapore. My thoughts are evolving and I am interested in more info/opinions.

 
Health facts about farmed salmon:

• The fat of farmed salmon is lower in omega 3 than wild caught (about 17% vs 27% by weight).
• However farmed salmon tends to be a lot fatter than wild caught (35% more fat) so it can have overall higher levels of Omega 3 per serving
• The Omega 6:3 ratio is better (ie it’s lower) in wild caught salmon because aquaculture feed tends to be high in vegetable oils and oilseed.
• Wild caught is richer in vitamins:
  • Vit D – 8x more
  • Vit A – 4x more
  • Potassium – 2x
  • Iron – 3x.
• However wild salmon tends to have higher levels of mercury.
• The fat of farmed salmon can store toxins like DDT, PCBs and asbestos.
• The flesh of farmed salmon is a naturally unappetising grey in colour. They are therefore given feed which changes the flesh colour to a more marketable pink. The feed may contain astaxanthin which is an antioxidant found naturally in algae and is healthy. However some farms use an artificial petrochemical-based dye.

 
Environmental Issues

• Salmon farming can pose a threat to wild populations through the spread of disease and parasites.
• While over fishing possibly constitutes a bigger threat, the American Pacific Northeast wild fishing industry is managed sustainably and is certified by the Marine Stewardship Council.
• Feed stock (like sardines and jack mackerel) for the growing salmon industry is depleting the wild species. It can take 3kg of sardines to make 1kg of salmon.
• Environmentalists recommend eating smaller fish which is more sustainable given this food chain effect
• On the bright side, farmed salmon standards are reported to have improved over time.

 
About toxins in farmed salmon.

• PCBs are found at levels many experts consider safe for human consumption. (“50-70 times lower than acceptable levels“)
• A 2004 peer reviewed study found PCBs in farmed salmon were 8 times higher than wild caught (36.63 parts per billion vs. 4.75) but still well below the 2000 ppb FDA limit).
• Dioxins (like PCB) accumulate in the body over time, taking several years to break down. So the impact of long term elevated exposure is as important as short term food contamination. Dioxins tend to increase five-tenfold from age 20-60. Total levels of dioxin measure in populations have decreased dramatically since the 1970s due to better pollution controls.
• PCBs are concentrated in the salmon’s skin and the fat directly underneath but this may be because that is also where most of the fat is. The EPA recommends that fish is cleaned of fat, skin and internal organs before consumption. This can reduce containments by up to 75%.
• Farmed salmon is, for most people, the largest source of such toxins in their diet with up to 40 times more PCBs than other foods.
• Studies have linked even low levels of PCBs to cancer, metabolic syndrome, obesity and type 2 diabetes.
• Some believe that, on balance, the abundance of Omega 3 in farmed salmon outweighs the presence of toxins
• One recent study of farmed salmon concluded that PCB levels would have to drop by 90% in order for it to be safe to consume 2 servings per week – ‘roughly 800,000 US adults are 100 times over their lifetime allowable cancer risk by eating this contaminated salmon (source)‘

 
What are the government guidelines on PCBs?

• The average level of PCBs in salmon is 27 ppb (parts per billion)
• FDA: The current Food and Drug Administration limit of PCBs in all fish is 2000 ppb
• Health Canada: The current Health Canada guideline for PCBs in fish is 2000 ppb.
• EPA: The Environmental Protection Agency guideline on PCBs is much stricter. They recommend that fish with PCB levels between 24 to 48 ppb should be eaten up to a maximum of 32 oz a month (4 weekly meals of 8oz fully cleaned of fatty tissues). The EPA number is based on cancer risk accumulation over a 70 year lifespan given weekly consumption.

(source)

(based on 8oz servings)

 
Salmon in Singapore

• Amost all (95%+) of the salmon found in Singapore grocery stores and wet markets is farmed from Norway (my observation)
• Farmed salmon sells for ~$40/kg at Cold Storage (wet markets differ little). Canned wild caught costs $35-$65/kg.
• The Fishwives brings in NZ King Salmon every month or so at about twice the price of farmed ($70-90/kg). It is also farmed and reportedly fed byproducts of abattoirs and poultry processing. In 2004, the AVA banned the import of King Salmon for a time due to contamination with Listeria. Claims by the producers of King Salmon that it has unusually high concentrations of Omega 3 have been dis-proven in independent studies. The levels in such salmon are on par with farmed salmon from other countries. However as NZ has no wild populations of salmon, it is claimed that salmon farming has less impact on the environment than farms in other regions. Also because of the farming method, less cage density means they do not use antibiotics, vaccines, hormones or chemicals used in other farms.
• After Russia banned Norwegian salmon for a while due to claims that it had heavy metal poisons, the Singapore AVA tested Norwegian salmon entering the country and said it tested negative for heavy metals.
• Likewise after radiation fears of salmon from Japan, the AVA tested imports and gave the all clear
• In 2001 the AVA said that the level of PCBs in salmon coming to Singapore was within WHO safe levels.

 
Questions & Further research:

• Are there recent stats on comparisons of toxins from various producers globally? For instance is there data to suggest that it is better to get farmed salmon from Tasmania than from Norway? This article and this one suggest that salmon farmed in Washington State, British Columbia & Chile is safer than that from Scotland, The Faroe Islands and Norway. I cannot find the primary evidence for this but it appears to come from the 2004 study.
• Are there any stats on PCBs in salmon from New Zealand and Australia?
• Given how much the industry has grown, why hasn’t another study been conducted like the one in 2004?
• Why isn’t farmed salmon from New Zealand or Australia available in Singapore?
• What safety testing does the AVA do on imported salmon? Given the occasional bans, some testing is being done. But why aren’t the results made public?
• How much does frozen wild caught cost in Singapore?

 
Thoughts*

• It is difficult to assess the risk of eating farmed salmon from the local grocery store without testing for toxins and publication of results
• To avoid this conundrum altogether (ie get omega 3 or avoid PCB?), it may be easier to just supplement with Omega 3 choosing a source that is purified to remove toxins. One serving of salmon gives you 3-4 grams of Omega 3 – about the amount I would normally consume in 3-4 days of supplementation. Supplementation is far cheaper than eating salmon even with very expensive brands. But fish consumption brings many more benefits than the provision of this one EFA. The “whole food” benefit would be lost.
• It seems advisable to reduce consumption of farmed salmon to 2-3 servings per month tops until there is better information available. Smaller fish should be consumed as a substitute.
• When eating farmed salmon, the skin should be discarded along with the fat underneath
• With a reduction store-bought salmon, eating wild caught 1-2 times per month is more affordable

* Note that I currently consume farmed salmon about 5-6 times per month.

Note:

Omega-3 requirements for adults vary by gender. According to the Institute of Medicine, women require at least 1,100 milligrams of omega-3s each day, men need at least 1,600 milligrams, pregnant women need 1,400 milligrams and breastfeeding women require at least 1,300 milligrams of omega-3s every day. The American Pregnancy Association encourages all adults to consume at least 500 milligrams of a combination of DHA and EPA every day, with a minimum requirement of 220 milligrams of DHA and 220 milligrams of EPA each day. – source

This amount can be met by a 150g serving of many different types of fish.

The famed 2004 study: Stokstad, TOXICOLOGY: Salmon Survey Stokes Debate About Farmed Fish, Science 2004 303: 154-155