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Welcome to PSR's Environmental Health Policy Institute, where we ask questions -- then we ask the experts to answer them. Join us as physicians, health professionals, and environmental health experts share their ideas, inspiration, and analysis about toxic chemicals and environmental health policy.


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Don’t Blame the Fish! And, don’t prescribe fish.

Posted on February 24, 2011

By Boyce Thorne Miller and Niaz Dorry

This essay is in response to: How does our food production system drive our exposure to toxic chemicals?

Consumer advisories warning the public to limit their intake of particular fish because they contain high levels of certain chemicals are ubiquitous. On the other hand, the medical community, nutritionists, and government agencies in this country prescribe frequent fish consumption for Omega-3 fatty acids and other positive health factors. Lost in this sea of incongruity is the fate of the marine animals that on one hand are being vilified as the enemy of human health because they’ve been poisoned by human induced industrial pollution and on the other are eaten by humans because of their health benefits.

It’s time to stop blaming or prescribing fish and ask ourselves the following questions: what are the persistent pollutants found in some marine animals doing to the health of the animals themselves? Could it be affecting the cognitive, reproductive and immune systems of marine animals such as tuna? Just like the people who eat them, could they be suffering health impacts as they become the conduit for toxic human products and wastes back to people? What does producing seafood for mass consumption do to the marine environment? And, finally, what are the human health implications of industrial scale fishing and seafood production – which is the strategy promoted by aquabusiness (agribusiness’ equivalent on the water) in order to meet the rising tide of health agency recommendations for increased seafood consumption? This last question should be at the forefront of our minds as human health and marine conservation advocates.

Much of the public dialogue about toxic exposure from seafood is centered on vilifying the fish with calls to stop eating fish like tuna, famous for containing mercury amongst other persistent bioaccumulative toxicants (PBTs). The more sophisticated conversation calling for a ban on the introduction of PBTs through clean production strategies is pretty much contained within the environmental health movement. In other words, the public discussion is about addressing the symptoms of a widespread epidemic – toxic chemicals in our food. The emphasis is on eating food that is presumably free of toxins, rather than real prevention by stopping the source of pollutants in our natural foods.

Rachel Carson best captures this epidemic when she said, “As crude a weapon as a cave man's club, the chemical barrage has been hurled against the fabric of life.”

Carson sounded the alarm about toxicants on behalf of the wildlife first. But governments and regulatory agencies would not take seriously the impact of these chemicals on the health of the fish, whale, or bird populations. We’ve since learned that ignoring the impact of these toxicants on the animals means ignoring the health of our own food chain. By allowing them to be poisoned, we only continue to poison our own bodies.

We began shifting the debate in the 1980s by bringing the focus onto human health, but in the process we forgot that wildlife are really on the front lines of the fight against chemicals in our food. By tracing the sources of contamination in humans, the connection between the health of animals and humans has become clearer. In fact, we believe environmental pollutants comprise one of the major hurdles the marine food web is facing today. And that food web often culminates with humans. 

A public outcry in opposition to toxic marine pollution and the production and use of chemicals complicit in that is essential if we are to protect our marine based food system. And, health advocates need to be part of this movement if they are going to continue prescribing seafood as a remedy for human health problems.

Cleaning up our coastal waters and restoring coastal habitats would help bring back depleted fish populations to areas fished by local fishing communities and would contribute to healthful local and regional seafood markets. But coastal waters are on the receiving end of much of the PBTs from land based sources. We hope the increased interest in adding seafood to healthful diets will bring about actions that improve local marine habitats for fisheries. But we are concerned that without a public outcry and support of health professionals, the trend might shift from cleaning up our act to scouring the global markets for fish caught or grown in poorly managed industrial fisheries and aquaculture around the world. As a result, all too often people are choosing farmed seafood, especially salmon, thinking they are improving their diets and their health.

Farmed Salmon Spawning a Toxic Blue Revolution

The new drive to eat more fish has caused unfettered growth of industrial scale fish farming, particularly salmon farming, in waters wherever they can be grown around the world:  Chile, Norway, Scotland, Canada, and Faroe Islands most commonly, and to a more limited extent the US and a few additional European countries. Other popular carnivorous fish like cod and halibut are also being farmed on small research scales but about to go commercial.  And a US company is trying, with apparent success, to put a genetically engineered salmon into farms for global marketing. 

There are many things wrong with this picture. Very often the health and survival of a diversity of wild fish are being threatened and the human health advantages proclaimed aren’t even being realized: 

  • Farmed salmon has a significantly decreased ratio of Omega-3s to Omega-6s (which have negative health impacts), due to the diet they are fed and the stress they are under. In salmon farms, substitute feed using terrestrial plant protein like soy meal (a current proposal) would markedly alter the healthfulness if not the taste of the fish, and Omega-3s would be diminished even more. Omega-3s in the fish we eat come from the food organisms they eat (small fish and crustaceans), which in turn get it from their food -- marine phytoplankton (microscopic plants). 
  • Market demand for salmon is being used by companies to introduce genetically engineered salmon into the aquaculture industry, with the added potential of negative health impacts from the introduced genes. While the genes used may be from other fish species that are safely edible, we don’t know what the impact of putting them into salmon might be – beyond the faster growth and larger size for which they are intended. Genes are complicated and new gene interactions may switch on other chemical processes that are not desirable. We just don’t know.
  • Since fish farms are most often located in coastal ocean waters, they are subject to the same exposure to toxic chemicals as wild fish. Therefore, farmed fish are equally as contaminated as wild fish, and could be more so if they happen to be located in contaminated areas and/or if feed is contaminated. Salmon feed may be contaminated with toxic substances and farmed salmon are routinely treated for diseases and parasites.

Regardless of whether fish come from fishing boats or sea farms, the more processing they undergo and the longer the distance and time they travel once they are caught, the more the health benefits are diminished. So fresh caught local fish may indeed be a boon to the health of local consumers, but people who don’t have such access should be offered other foods with similar health benefits, which just might involve redesigning local agriculture – a concept already afoot by the local food movement.

So what should we eat from the ocean?

  • Eat a variety of seafood. After all, the ocean is a diverse ecosystem and if we are to eat from it, our diet should reflect its diversity to the extent that it does not undermine the integrity of the ecosystem.
  • Eat low on the marine food chain.  The ocean is a fish-eat-fish world and much of the pollutants are passed onto bigger fish through their diet.
  • Eat wild fish. Aquaculture is riddled with practices using pesticides, hormones and other toxic chemicals known to have adverse affects on human health.
  • Eat seafood that is local to your region and still looks like what it did when it was alive. Processing and preservation mechanisms often involve chemicals we don’t want or need in our bodies.

And, most importantly, fight for the health of the marine animals -- because their health is directly connected to ours.

If the health benefits of fish are to be promoted by the medical profession and others, the prescription to eat fish should clearly be accompanied by guidelines that are beneficial to the consumers and operate within the capacity of the wild ocean.


Boyce Thorne Miller and Niaz Dorry said ..

In response to the two comments in defense of farmed fish, may we first make clear the perspective that framed our essay: we support the recovery and maintenance of wild fish populations, healthy & well-managed fisheries, and biodiversity in marine ecosystems worldwide. We believe these ecosystems have a real but limited capacity to provide healthful food and should be used for the greatest benefit to communities who depend upon their resources. That’s our mission. With that in mind, we provide the following additional information and references. We should start by saying our original piece and the comments here are focused on marine-based, industrial scale finfish farming. We do agree that some shellfish farming done at the scale that complements the marine environment actually has benefits. But when it comes to industrial scale marine finfish farming there is no doubt in our minds that the risks outweigh the benefits. The practice often floods the market with fish undermining fishermen by driving market prices so low that community based, small and medium scale boat fishermen cannot survive. And, that’s just the tip of the economic and social iceberg. We’ll leave the questions around labor practices, numbers of jobs, economic ripple effects in coastal communities, etc. to another day. And then there are ecological consequences, which we barely touched upon in our essay. One commenter talks about myths. The biggest myth about the sea farming of finfish is that it reduces the fishing pressure on wild fish and thus helps them recover and flourish. Due to several facts of ocean-based fish farming, the activity actually contributes to the decline of some fish populations. “The benefits of farming carnivorous fish have been challenged; extensive research on salmon has shown that farming such fish can have negative ecological, social, and health impacts on areas and parties vastly separated in space. Similar research is only beginning for the new carnivorous species farmed or ranched in marine environments, such as cod, halibut, and bluefin tuna.” (Naylor and Burke, 2006) Furthermore, increased farmed carnivorous fish farms have increased the demand for fish meal, which comes from the wild catch of small forage fish through factory fishing operations using both industrial scale trawls and purse seines. These factory boats are catching what would otherwise be feeding wild carnivorous fish. Proposals to feed farm salmon vegetable protein from land instead are puzzling, since to keep the omega-3s at desirable levels, significant fish oil (from wild fish) would have to be added, and it is doubtful that a carnivore can survive healthfully on a vegetarian diet. Instead of turning salmon into chicken, why not eat chicken? However the factory trawlers are actually increasing as farmed carnivorous fish increase the demand for fish meal which comes from the wild catch of small forage fish that would otherwise be feeding wild carnivorous fish. Proposals to feed farm salmon vegetable protein from land instead of fish meal are puzzling, since to keep the omega-3s at desirable levels, significant fish oil (from wild fish) would have to be added. Also, it is not clear a carnivore can survive healthfully on a vegetarian diet. Instead of turning salmon into chicken, why not eat chicken? Furthermore, it is well documented in Norway that a parasite called sea lice, is a severe problem that is managed in fish pens by pesticides. British Columbia also has well documented occurrence and treatment of sea lice. Fish farmers regularly have to treat their fish with a variety of chemicals to reduce the number of sea lice on their fish. These chemicals can be mixed in the feed or distributed directly to the net pens as emulsions. Parts of the sea lice populations are exposed to sub lethal doses of the anti-parasite medicines and may develop immunity to the treatments. Aquaculture in Norway is so extensive that wild fish biologists have become alarmed at the observation that wild salmon are becoming infected with sea lice at lethal levels. Similar concerns have been reported in published literature in British Columbia, Scotland and Ireland. Salmon smolts migrate out of their rivers into the sea often passing close to dense collections of salmon farms. In addition, sea lice can survive and be carried on currents for long distances without a host, so the potential for spreading to wild salmon is great. Furthermore, salmon escape in large numbers from cages and are incorporated into wild populations. The decline of wild salmon and the increase of feral farmed salmon has been well documented. FAO reported in 2005 that a third of the salmon living in Norwegian waters were of farmed orgin and that is likely a serious underestimate for today. We know that some 400 million farmed salmon are stocked each year in 1000 fish farms in Norway and that number is rapidly expanding. Compared to that, an estimated 400 thousand wild salmon return to Norway’s rivers each year, and that number is dropping. The outlandish ratio of 1000 farmed salmon for every wild one doesn’t give the wild salmon much of a chance. While the occurrence of massive escapes has decreased, they still occur (we just received information that there has been a big escape in Norway of 175,000 farmed salmon, which is close to 50% of the spawning population of wild salmon in all of Norway.) Equally important is an unmonitored continuous leakage of a few fish at a time, which can become significant with so many farms operating. In British Columbia, escapes large and small have the added impact of introducing a new species to compete with wild salmon populations. Similar disease situations have been reported on the west coast of Canada and in Scotland and Ireland. The east coast of Canada is now reporting sea lice on farmed salmon and there is some treatment for the parasite. Almost all countries where salmon is grown now require treatment for sea lice when they are found in specified trigger concentrations on farmed fish. To say it is not routinely done is to say the regulations are being ignored. And in Chili, the second largest producer and source of much of farmed salmon in US markets, salmon farming is highly unregulated and poorly monitored. Alarm has spread since Norway announced in the past couple of years that sea lice are showing immunity to all known treatments, and there is genuine fear among fisheries biologists that the problem will soon be uncontrollable in pens, so they will become an even greater source of the parasite to wild populations (where it has never been under control). There are also other diseases such as the freshwater parasite Gyrodactylus that can infect and be spread by young hatchery salmon, and infectious salmon anemia, which is treated with antibiotics. As for the Omega-3 content of farmed vs. wild salmon, there seems to be agreement among several sources that farmed salmon have significantly more fat in equivalent pieces of meat and that that fat contains a lower percentage of Omega-3 and a lower ratio of desirable Omega-3 to undesirable Omega-6 fatty acids. (e.g. Ball and Paone, 2001 referenced in Weber, 2003). It should be said, however that if equal weights of flesh of the two are compared the total weight of Omega-3 is only slightly lower in farmed fish because of the significantly higher fat content. So I guess it depends on how you want to get your Omega-3s. As for PCBs and other bioaccumulative toxics, I don’t believe that we ever said farmed fish is always more contaminated than wild fish. There are some studies that show it might be a concern, but we agree with you that the problem may exist in either farmed or wild salmon and other fish and is not uniform. If salmon happen to be penned in contaminated waters they are likely to accumulated higher levels of contaminants than fish that are just swimming through. But again we blame the polluters, not the fish. References: APHIS Veterinary Services, Infectious Salmon Anemia Tech Note. 2002, US Department of Agriculture. F. Burka, .et al, Mechanisms of resistance development to emamectin benzoate (SLICE®) in sea liceJohn Atlantic Veterinary College, University of Prince Edward Island, Canada. Power Point presentation. Felipe C. Cabello. 2006. Heavy use of prophylactic antibiotics in aquaculture: a growing problem for human and animal health and for the environment. Environmental Microbiology 8:1137-1144. Serena Black, 2010. Coastal Alliance for Aquaculture Reform. "Sea Lice." Farmed and Dangerous. . Dannevig, B.H. and K.E. Thorud, Other viral diseases and agents of coldwater fish: infectious salmon anemia, pancreas disease and viral erythrocytinecrosis, in Fish Diseases and Disorders, Volume 3, Viral, Bacterial and Infections, P.T.K. Woo and D.W. Bruno, Eds. 1999, CAB International: Wallingford and New York p. 149-175. FAO. © 2005-2011. World inventory of fisheries. Impact of aquaculture on biodiversity. Issues Fact Sheets. Text by Devin Bartley, Heiner Naeve, Rohana Subasinghe. In: FAO Fisheries and Aquaculture Department [online]. Rome. Updated 27 May 2005. The Fish Site. 2008. Ford, J.S. & R.A. Myers. 2008. A global assessment of salmon aquaculture impacts on wild salmonids. PLoS Biology. 6(2): e33. Johnson, S.C., Crustacean Parasites, in Diseases of Seawater Net pen-reared Salmonid Fishes, M.L. Kent and T.T. Poppe, Editors. 1998, Fisheries and Oceans Canada: Nanaimo, BC. P. 80-90. Krkošek, M., Ford, J. S., Morton, A., Lele, S., Myers, R. A. and Lewis, M. A. (2007). Declining wild salmon populations in relation to parasites from farm salmon. Science 318: 1772-1775 M. Krkoˇsek A. Bateman, S. Proboszcz, C. Orr. 2010. Dynamics of outbreak and control of salmon lice on two salmon farms in the Broughton Archipelago, British Columbia. Aquaculture Environment Interactions, 1: 137–146, 2010 Larry Lack, Working Waterfront, March 15, 2011. New Brunswick sea lice pesticide treatment generates opposition. Island Institute. Morton, A., A. McConnell, R. Routledge, & M. Krkosek. 2011. Sea lice dispersion and salmon survival in relation to fallowing and chemical treatment on salmon farms. ICES Journal of Marine Science. 68, 144-156. Morton, A. and R. D. Routledge (2005). Mortality rates for Juvenile Pink Oncorhynchus gorbushca and Chum O. keta salmon infested with Sea Lice Lepeophtheirus salmonis in the Broughton Archipelago. The Alaska Fisheries Research Bulletin. 11(2): 146-152 National Academy of Sciences (NAS). 2003. Dioxins and dioxin-like compounds in the food supply: Strategies to decrease exposure. NAS Institute of Medicine, Food and Nutrition Board, Committee on the Implications of Dioxin in the Food Supply. The National Academies Press. Washington, D.C. Rosamond Naylor and Marshall Burke. 2005. AQUACULTURE AND OCEAN RESOURCES: Raising Tigers of the Sea. Annual Review of Environment and Resources, Vol. 30: 185-218 U.S. Department of Agriculture, Agricultural Research Service. 2002. USDA National Nutrient Database for Standard Reference, Release 15. Nutrient Data Laboratory Home Page. And the reference the commenter forbade us from citing: Hites, RA, Foran, JA, Carpenter, DO, Hamilton, MC, Knuth, BA, and Schwager, SJ. January 9, 2004. Global Assessment of Organic Contaminants in Farmed Salmon Science: Vol. 303 no. 5655 pp. 226-229

March 15, 2011
Jeremy Twigg said ..

Posted by Jeremy Twigg (@CDNaquaculture) on behalf of Ruth Salmon: As a representative of Canada’s aquaculture industry – which farms finfish and shellfish in our nation’s oceans and lakes – I wholeheartedly support efforts to eliminate persistent bioaccumulative toxicants (PBTs) from industrial processes. In the meantime, people have to eat. Seafood – both wild and farmed – is an excellent protein choice that’s low in saturated fat. Farmed seafood has the added benefit of talking pressure off wild stocks. While your article contains some interesting perspectives, misinformation about farmed seafood will needlessly scare consumers away from this heart-healthy protein. Most importantly, no hormones are used by Canada’s aquaculture industry. When it comes to seafood, PCBs – which are a common type of PBT – receive a lot of attention within the context of farmed salmon, but wrongly so. Research shows that contaminants found in farmed salmon fall far below both Canadian and American acceptable levels. In fact, levels of PCBs in Canadian farmed salmon are lower than in other commonly eaten foods such as beef, chicken, pork, eggs, and butter. It’s also important to point out that farmed and wild salmon contain similar amounts of omega-3 fatty acids. Further, Canadian feed manufacturers have developed feeds that are replacing some of the fish-based ingredients with those from alternate sources, such as vegetables – yet still provide high quality, nutritious farmed salmon with no significant reduction in the amount of heart-healthy omega-3 fatty acids in the fish. Regarding the issue of genetic enhancement, the Canadian aquaculture industry does not support the commercial production of transgenic fish for human consumption. We firmly believe that Canada’s current fish breeding practices enable the production of quality products that are in high demand from both domestic and international markets. Your advice to ‘eat a variety of seafood’, however, is probably the best take-away. Farmed salmon should be part of that choice. Ruth Salmon Executive Director Canadian Aquaculture Industry Alliance

March 1, 2011
Kelly Nokes said ..

Hi Boyce and Niaz; Unfortunately, you both seem to parrot many myths about aquaculture, and neglect to provide any credible sources for your assertions. The focus on salmon, and the 'ask' that folks choose wild salmon over a farmed product comes across as yet another promotion of one industry over another. I certainly hope this isn't the case. 1. Can you please provide published research that supports your claim that farmed salmon have decreased ratio of Omega 3/6, and that this therefore 'markedly alters the healthfulness and taste'. 2. Please provide published sources that confirms farmed salmon (and wild salmon for that matter) are a risk to consumer due to exposure to toxic chemicals. Note - do not just cite the Hites et al(2004) study as this study is not only dated, but it doesn't prove either wild/farmed salmon are a risk (FDA), and many follow up studies have noted the further reduction in contaminents found in fish feed and the positive results. 3. Aquaculture is practiced around the world, with different regulation regimes in each region. For you to suggest that all producers "routinely treat for disease and parasites" is not only unfair, but your inability to quantify "routinely" is quite concerning. Please provide antibiotic use for each region you note that produces farm-raised salmon. I look forward to your response. Kelly

March 1, 2011

To answer your question about supporting your "small local fisherman" wich I am one of, this current administration wants to put the small scale community food producers out of business and replace it with a few large opperations that they can "manage" how the government/enviros see fit. A perfect example of this is the "catch share" push by NOAA that 98% of fisherman in this country dont want! America wake up and support your local small scale food producers while were still here, unless of course you prefer the special of the week at your "local" Super WalMart!!!!!!

March 1, 2011
P.Harris-Swenson said ..

I believe that more people would eat organic and wild if it were less expensive than agri-business products. When will we support with our taxes the healthier small organic farmer and fishermen who would put healthier choices on our tables for less instead of the large agri-farmers who put corn & soy into everything?

February 26, 2011

Comments closed.