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Vol. 4, No. 2, 2005
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Despite assurances from the B.C. Salmon Farmers Association, the use of antibiotics and other medication to treat farmed salmon is a significant issue. In 2003, the total amount of antibiotics administered to B.C. farmed salmon was twice what it was in 1995.

Fish treated with antibiotics (or other medicated feed) cannot be harvested for food for a certain period of time -- called a withdrawal time. The withdrawal time will vary, depending on the type of drug used and water conditions. Antibiotics are not the only drugs used in salmon farming; there are a total of nine drugs, called therapeutants, which are approved for use in Canada in hatcheries and on salmon farms. Health Canada has also approved the fish sedative Aqua Life-TMS, and several sea lice treatments.


Heritage markets its farmed salmon as “pure and simple.” Here are some “pure and simple” facts, revealed by court documents, about the use of drugs in Heritage operations in Maine in 2002.

• Heritage feeds its salmon a meal containing waste products from the chicken processing industry, which includes chicken feathers, chicken blood, and chicken carcasses.

• Heritage salmon feed also contains soybean meal, wheat, a “vitamin/mineral pack” and other ingredients.

• Heritage adds to the feed a pharmaceutically manufactured pigment called canthaxanthin, which colors the fish’s flesh pink.

• Nets on Heritage salmon pens are treated with an antifoulant called Flexguard 11, which contains copper.

• Bacterial infections in Heritage salmon are treated by adding the antibiotics TM 100 and/or Romet to salmon feed.

• A chemical called cypermethrin, contained in a product called Excis, is used by Heritage to treat sea lice. To apply the cypermethrin, Heritage confines salmon in a small area with a tarp and pours in the chemical. Following the hour-long treatment, the tarp is removed and the cypermethrin is released from the net pens into the marine environment.

In June 2003, Heritage and Stolt Sea Farm faced a large and significant lawsuit in the state of Maine. The suit, brought by the U.S. Public Research Interest Group, accused the two salmon farming companies, along with Atlantic Salmon of Maine, of discharging pollutants into the ocean without appropriate permits. Heritage reached an out-of-court settlement, agreeing to comply with a number of stringent conditions aimed at reducing the environmental impact of its salmon farms. Heritage also agreed to pay $375,000 to fund wild salmon restoration (Atlantic salmon have been on the U.S. endangered species list since 2000) and an equal amount in legal fees to the U.S. Public Research Interest Group. Furthermore, Heritage agreed to fallow sites, to stop raising European salmon strains, to ban experimental drugs without an environmental review and to stop using prophylactic antibiotics in salmon feed.

In 2003, more than 37 million Canadian farmed salmon were treated with Slice, according to documents obtained under the federal Access to Information Act (this figure may include individual salmon treated more than once). In 2002, more than 47 million farmed salmon were given feed medicated with Slice; in 2001, that number exceeded 38.5 million.50

Health Canada originally approved the use of Slice as an emergency drug treatment on the condition that no emamectin benzoate residues were found in farmed salmon during routine inspections by the Canadian Food Inspection Agency (CFIA). However, CFIA documents obtained under the federal Access to Information Act show that emamectin residues were commonly found on New Brunswick farmed salmon during 2000, even though companies and their veterinarians had adhered to prescribed withdrawal times and dosages: “. . . We are consistently finding drug residues,” wrote Glenn McGregor of the CFIA in December 2000 to Gerard Lambert of Health Canada’s Human Safety Division, adding that, “We are prepared to sample and detain each shipment if necessary, but this will disrupt the orderly marketing of the product.” In other correspondence, CFIA staff asked Health Canada if they should issue a recall or notify the public following the discovery of emamectin benzoate residues in farmed salmon. As 2000 drew to a close, Health Canada made a decision about the residue problem. Instead of a zero tolerance policy, Health Canada decided to accept emamectin residues in farmed salmon up to a maximum of 50 parts per billion, as long as the prescribed seven-day dosage and 25 day withdrawal time were followed.

Since Slice is administered in feed, it is not considered to be a pesticide, unlike some other sea lice treatments. Aquaculture veterinarians generally portray Slice as a safer and more effective drug than other sea lice medications. Schering-Plough, the global pharmaceutical company that manufactures Slice, describes how the medication works:

When fed to fish, emamectin benzoate is absorbed from the gut and distributed to the tissue of the fish. When sea lice feed on tissues of treated fish, emamectin is taken up into the tissues of the louse. Emamectin then binds to ion channels of nerve cells and disrupts transmission of nerve impulses, which results in paralysis and death of the parasite.

Each year from 2000 though 2003 Health Canada approved between 123 and 168 requests from aquaculture veterinarians to use Slice on an emergency basis.53 Even if sea lice is found in just one pen of salmon, all salmon on the farm must be treated. Schering-Plough Corp, the global pharmaceutical company that manufactures Slice, also recommends that neighboring farms coordinate Slice treatments in order to ensure maximum efficacy.

The salmon farming industry and its backers claim Slice is a “safe, effective drug treatment [that] is used to combat sea lice in a way that minimizes environmental impact.” However, little is known about the long-term impact of Slice on other aquatic life. Mounting evidence indicates that Slice may negatively affect crustaceans. One academic study showed emamectin benzoate to be lethal to lobsters at high doses; Schering-Plough notes that at seven times the recommended dosage Slice is, in fact, lethal to salmon. A recent study published in the Canadian Journal of Fish and Aquatic Sciences concluded there is “conclusive proof that emamectin benzoate is disrupting the endocrine system that controls molting in the American lobster.” In a cautionary message, the study’s authors wrote that, “Crustaceans are more sensitive to emamectin benzoate than are other marine invertebrate . . . and fishermen are concerned about the impact of this chemical on lobster and crabs foraging beneath salmon cages. Almost nothing is known about the sublethal responses of crustaceans to emamectin benzoate or other avermectins.

FACT: 27.7 metric tones of antibiotics were used by the B.C. aquaculture industry in 2003.

FACT: Chilean salmon farms use one hundred times more antibiotics in salmon production than do salmon farms in Norway. In 2001, 40,000 kilos of antibiotics was given to farmed Chilean salmon in feed, compared to 645 kilos in Norway.74

Consumers of farmed salmon, like consumers of pork, beef and poultry, may also ingest antibiotic residues and, in the case of farmed salmon, Slice residues. Although all residues found during routine testing of B.C. farmed salmon since 2000 appear to have been within Canadian legal limits, consumers who prefer not to ingest any drug residues at all have no way of knowing if the salmon they buy have been medicated. The Canadian Food Inspection Agency tests approximately 100 farmed salmon samples annually for emamectin benzoate residues. Each sample consists of five fish, meaning that 500 farmed salmon are tested each year for Slice residues. This amounts to residue testing on just a tiny fraction of the salmon dosed with Slice each year.

During routine testing by the Canadian Food Inspection Agency in 2000, salmon farmed on Canada’s Atlantic coast were found to have emamectin benzoate residues of up to 8 parts per billion (ppb).72 Allowable residue levels in Canada are set at 50 ppb. In the United Kingdom, the MRL for emamectin benzoate is considerably higher, at 100 ppb. However, maximum residue limits (MRLs) for emamectin benzoate residues in meat (such as beef) are set much lower by the U.S. Environmental Protection Agency (2 ppb).

It's Not Easy To Find Out What's In Farmed Salmon
by Stephen Hume
© The Vancouver Sun, Dec., 2004

When the Raincoast Conservation Society's 105-page report on British Columbia's salmon farming industry landed on my desk with a thump, I was tempted to leave it on the slush pile.Christmas is a week away, kids are out of school and who wants to spend evenings ploughing through tables distilled from financial statements, analyses of taxpayer subsidies or dreary statistics about fish prices and regulatory regimes?

But this study caught my attention with its reference to the use of a potent chemical to treat farmed salmon for infestations of sea lice, a problem environmentalists have made considerable noise about but which the authorities in the provincial and federal governments play down.

Environmentalists argue that while sea lice afflict all salmon, wild fish are normally less susceptible because they disperse during much of their life cycle, making themselves less vulnerable to parasites. Farmed fish, on the other hand, are confined to densely populated cages where infestations occur more easily. Furthermore, the argument goes, by parking all the hosts in one place, the parasites may reproduce more easily because there are more breeding partners available.

Thus, the environmentalists say, net pens for domestic salmon mean clouds of sea lice hanging around waiting to latch onto their free lunch. And when immature wild salmon migrate past the pens on their way to the open ocean, they become particularly vulnerable because they are small and not able to survive the excessive parasite loads they wouldn't otherwise encounter.

The official position has been that links between fish farms, sea lice and mortalities among immature wild salmon are not proven, that more study is needed, indeed, that wild fish may themselves be responsible for the infestations at salmon farms, etc.

That debate aside, what makes the Raincoast report fascinating is its assertion that federal records show that over the past five years fish farmers have treated about 170 million salmon -- 35 million of them last year alone -- with the chemical employed to kill sea lice.

This is a mind-boggling number. If the average mature salmon is about a metre long, then nose to tail on the equator, the chemically treated fish would go around the world 4 1/4 times.

Which prompts the question: If sea lice infestations at fish farms are not a major problem, why the need for such massive, extensive and sustained prophylaxis?

The active ingredient in the treatment is emamectin benzoate, normally used as a topical pesticide in field crop agriculture but on fish farms administered orally in the salmon feed. Presumably, as the parasites feed on treated salmon they are killed by the chemical additive.

Which might explain why, according to the Raincoast report, Health Canada initially authorized the use of emamectin benzoate to treat farmed salmon for sea lice only on an emergency basis. It was to be administered for a strictly limited period, dosages were rigorously controlled and the treated fish could not be marketed for a defined waiting period -- and then on the condition that no residues could be detected in flesh intended for human.

However, the report cites federal documents it says confirm that even though fish farmers adhered to dosages and withdrawal times, the Canadian Food Inspection Agency routinely found residues of emamectin benzoate in slaughtered farmed salmon during 2000.

Inspectors even queried Health Canada about whether to recall product or to issue a public notice, acknowledging that sampling and detaining each shipment would disrupt the "orderly marketing" of the slaughtered salmon, the report says.

"Health Canada made a decision about the residue problem," the report claims. "Instead of a zero tolerance policy, Health Canada decided to accept emamectin residues in farmed salmon up to a maximum of 50 parts per billion."

Admittedly, this is a minuscule amount. But minuscule amounts can sometimes have much larger effects. As we saw in Thursday's front page headlines about contamination of feed for cattle destined for human consumption, a single particle the size of a grain of sand can infect a 550-kilogram steer with the brain-wasting affliction we call mad cow disease.

On this basis, it seems entirely reasonable for consumers to wonder about the possible implications of ingesting even trace amounts of a toxic chemical added to fish feed to kill parasites that feed on the same meat those consumers will subsequently eat.

All of which prompts another question: What effects does emamectin benzoate have on higher organisms than the crustaceans it is intended to kill?

When I went to the website of the provincial ministry responsible for fish farming and did a search on the chemical, I found only confusing and conflicting information. For example, I learned on one page that "there are no hormones or chemicals used on food fish in the B.C. aquaculture industry." Then I found a graph that indicated that the volume of emamectin benzoate used to control sea lice infestations had increased eight-fold since 1999.

Next, I found a statement that emamectin benzoate is considered a drug rather than a chemical but that "many farmed salmon are never treated with any medication throughout their entire life cycles." Another graph showed that the use of antibiotics has more than doubled since 2001.

The website assured me that the "Canadian Food Inspection Agency tests fish destined for market, for drug residues to ensure no trace of any medication is present" -- which is not what the Raincoast report says federal documents show.

What I couldn't find on either provincial or federal websites was easily understood information about the toxic effects of emamectin benzoate on higher organisms. That doesn't mean the information is not there, it just means that if a journalist skilled in web searches can't find it easily, it doesn't seem likely too many consumers and casual web users will find it, either.

However, at the safety information website of Oxford University's Physical and Theoretical Chemistry Laboratory, I did find the compound listed as "very toxic," having a half-life in the environment of up to 15 months and killing 50 per cent of rainbow trout after 96 hours at exposure levels of 174 parts per billion.

At the U.S. Environmental Protection Agency, I found reports on systemic toxicity of emamectin benzoate at a range of dosages in mice, rats, rabbits and dogs.

Among the effects: "marked neural degeneration," "tremors," " hind-limb splaying," "changes in brain and spinal cord, sciatic and optic nerves and skeletal muscles in males," "pathological signs of neuro-toxicity consisting of skeletal muscle atrophy and white matter multi-focal degeneration in the brains of both sexes," "increased incidence of severity of infections."

On the California Environmental Protection Agency site the compound was associated with "possible adverse effects" accompanied by numerous notations that there were gaps in the research knowledge.

I'm certainly not saying or even attempting to imply here that dosing farmed salmon with emamectin benzoate results in any elevated risk to consumers. I assume our health authorities, the manufacturers and the producers believe it doesn't.

But while I trust my doctor implicitly, I also expect her to make sure that I understand all the possible side-effects of what she prescribes so that I can decide what benefits outweigh what risks.

It follows that when any agricultural drug is associated with neurological effects in laboratory animals and is possibly present in the food chain - even at trace levels -- consumers deserve, and authorities have a duty to provide, a transparent, easily understood and easily located source for all the relevant information about that drug and the science behind its approval.

Related articles:
Teflon and your Toxicity
Retreat from Meat
Cell Phone Users Beware
The Soya Bean Conspiracy
Can Red Meat Take the Heat

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