SLICE AND SALMON LICE
RAINCOAST CONSERVATION SOCIETY
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
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.
SALMON: THE HARD FACTS -- TO SWALLOW
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
• 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.
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
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.
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.
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.
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
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
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.
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
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
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.
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
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.
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.
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."
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
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
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
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
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."
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.
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.