Download Human Health Risks Associated With Salmon Farming

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

October 9, 2001
Presentation to the Leggatt Inquiry
Jointly presented by Dr. Warren Bell of the Canadian Association of Physicians for the
Environment (CAPE) and Sergio Paone, Ph.D., Anima Mundi Environmental Consulting.
Human Health Risks Associated With Salmon Farming
Most of the salmon produced in BC now comes from open netcage farming rather than
traditional fisheries. In fact, it seems clear that the general policy direction of the Department of
Fisheries and Oceans favours the development of salmon farming. This shift introduces direct
human health risks and other negative impacts, some of which are similar to those associated
with the farming of land-based animals. The consumer's opportunity to select meats that are free
of these risks is being reduced. For farmed salmon these risks include:
Drug residues in farmed salmon and in other seafood, like shellfish, that are wild but
live in the vicinity of the salmon farm.
Increases in antibiotic resistance among bacteria carried by farmed fish, which can in
turn pass on resistance to bacteria that cause human disease.
Exposure of salmon farm workers to antibiotics and other chemicals used on the farm.
Changes in the nutritional value of farmed salmon relative to wild salmon.
Net loss of protein for human consumption as a result of feeding wild fish to farmed
These risks may be divided into two categories. Some risks, like chemical residues in
and the nutritional value of farmed salmon, are of concern mainly to the individual who
consumes it. Other risks, however, have broader global and social implications, and
should also be of concern to those who choose not to eat farmed salmon. In this second
category fall the risks such as the development of antibiotic resistance and the risk of
depletion of global seafood supplies.
Drug residues
Antibiotics, and other drugs, are administered to farmed salmon only when a disease
outbreak is identified. In contrast, other animal farming industries also administer antibiotics on
a prophylactic basis (to prevent disease from occurring) and as growth promoting agents (subtherapeutic levels of antibiotics, which increase animal rate of growth). The drugs are usually
administered as additives in the feed. In an effort to prevent drug residues in salmon heading for
market, a withdrawal time is mandated. This is to allow time for salmon to excrete the drug from
their bodies. The BC provincial Aquaculture Regulations state that salmon are not to be
harvested less than 105 days after being treated with drugs, unless federal Food and Drug
Regulations specifies a different standard or a veterinarian has prescribed a different minimum
withdrawal period (1).
The potential human health effects that are associated with drug residues are toxicity
allergic reactions and the development of antibiotic resistance in bacteria affecting humans.
Prior to 1997, it was the responsibility of the federal Department of Fisheries and Oceans (DFO)
to inspect farmed salmon for the presence of drug residues. This ended in 1997, when the
Canadian Food Inspection Agency CFIA) was created under Health Canada to, among other
duties, inspect all meats for drug residues.
In both BC and eastern Canada, the two main classes of antibiotic residues monitored are
sulfonamides and tetracyclines. In addition, as small number of farmed salmon in BC are tested
for ivermectin, a parasiticide used to combat sea lice. The CFIA compares the results of the drug
residue tests with the Minimum Recommended Level (MRL), a concentration established by
regulation. A particular batch of farmed salmon is considered to be a health hazard if the sample
shows drug residues above the MRL.
Three main issues with respect to the CFIA farmed salmon inspection program are:
The amount of harvested farmed salmon produced with drug residue levels above the
The reliability and thoroughness of the CFIA farmed salmon-testing program.
Actions is taken by CFIA when high drug residue samples were found.
We will now look at these three points in more detail.
How much harvested farmed salmon contains high drug residues?
Results of all tests for drug residues in farmed salmon were obtained from the Federal
government through a Freedom of Information Act search. Between 1997 and 1999, 0.4 to 1.1 %
of the farmed salmon tested in British Columbia showed drug residues above the MRL. For New
Brunswick, data was only available to us up to 1998. The fraction of samples in that province
that were above the MRL was 5.5% in 1997 and 1.5% in 1998. In Newfoundland, drug residue
tests were only conducted between 1990 and 1994 (with the exception of 1 fish each in 1997 and
1998, which is not statistically significant). From 1990 to 1994, an astonishing 29 to 50% of
farmed salmon tested showed drug residue levels above the MRL.
Although the percentage of farmed salmon contaminated with drug residue for BC and
New Brunswick is small, the amounts are significant when one looks at the weight of farmed
salmon that they represent. Table 1 summarizes this.
Table 1:Summary of farmed salmon production & amount produced with antibiotic residue
levels above the MRL for all provinces tested.
British Columbia
New Brunswick
Total Farmed
Amount produced with
antibiotic residue above
MRL (tonnes)
How reliable is the CFIA Farmed Salmon Inspection Program?
When looking at the above results for drug residues found in farmed salmon, one must
bear in mind that there are several identified problems related to how the CFIA conducts it's
inspections. A June 2001 report, by Minister of Public Works and Government Services Canada,
assessed the CFIA testing of aquaculture products (2). The report found that drug residue tests
were not conducted for all the drugs used on salmon farms. Also, the amount of testing did not
always reflect the level of production, or the pattern of drug use. Some important examples of
this are as follows:
Florfenicol is an antibiotic widely used on fish farms in BC, yet the CFIA has done
no analysis for residue. In 1999, 33% of all medicated feed in BC contained
A new drug, Emamectin Benzoate (not yet approved for this use, but available by
veterinary prescription), has been used in salmon farms in the Maritimes since1998.
Its residue is not being tested for even though, in 1999, 38% of all medicated feed in
the Maritimes contained this drug.
In March, July and October of 1999, no drug residue tests of any kind were conducted
in BC. This despite the fact that these three months accounted for 25% of farmed
salmon production and 28% of drug use for the year.
In the Maritimes, 31% of all residue tests for 1999 were conducted in December, a
month that accounted for just 12% of farmed salmon production and a mere 2 % of
drug use.
Response of the CFIA when high residue levels are found.
The stated purpose of the CFIA testing program is to prevent the public from being
exposed to the health risks associated with consuming farmed salmon with high drug residues.
Despite this formal commitment, the actions of the CFIA do not always clearly reflect such a
In the above mentioned assessment report of the CFIA(2), the response of the CFIA was
reviewed for eight recent cases where tests showed fish with drug residue levels above the MRL.
Most of the efforts of the CFIA went into investigating the root cause of the high levels.
However, their efforts in preventing contaminated farmed salmon from reaching the consumer
wholly inadequate. Some problematic examples are:
In only two of the eight cases of contaminated fish that the report reviewed, did the
CFIA initiate a farmed salmon product recall.
The time it took to get test results was up to several weeks, by which time the farmed
salmon had been sent to market, bought and consumed by the purchaser.
The criteria for recall used by the CFIA were not always clear. In one of the eight
recent cases, the Agency used a 1994 Health Canada health risk assessment which
gave 0.2 parts per million (ppm) as the 'safe' residue level for oxytetracycline this
conflicts with the standard of 0.1 ppm which was the MRL at the time of the test.
The CFIA also investigates consumer complaints related to illnesses from fish products.
Between 1997 and 1999, the CFIA assessment report reviewed 15 complaints that involved
farmed fish. They found that;
" in almost all cases, documentation was incomplete and that it was not possible to
evaluate the appropriateness of the investigations. We noted that in three cases, the
reported symptoms were allergic reactions, and there is no evidence to show that the
presence of drug residues, which are recognized to be potential allergens, was
investigated as a possible cause."
As currently conducted, salmon farming results in the production of some farmed salmon
with drug residue levels above the minimum recommended by Health Canada. The Canadian
Food Inspection Agency, under current programs, does not adequately sample for these drug
residues and does not prevent most of the farmed salmon it finds to be hazardous for consumers
from reaching market.
Drug residues in wild seafood.
Neither the CFIA nor the DFO routinely test wild seafood in the vicinity of salmon farms
for drug residues. Yet the drugs administered to farmed salmon do make their way into the
marine environment. A few studies have shown that these drugs also find their way into nontarget organism as well. Some findings from this research include (3):
88% of 189 fish caught in the vicinity of fish farms had levels of antibiotics above the
The presence of antibiotic residues above the MRL in wild fish caught up to 400
metres from a fish farm.
Drug residues present in mussels and oysters collected in the vicinity of fish farms in
Norway and Finland.
There is no program in Canada that monitors drug residues in wild fish near salmon farms. Such
a program would be useful in order to warn the public of times when the harvesting of wild fish
or shellfish near salmon farms should not be conducted. It would also clarify how much drug
residue is making its way into wild ecosystems, something that at present is completely
Antibiotic Resistance
It is well established that repeated use of antibiotics to treat bacterial diseases leads to
selection of and increase in the population of antibiotic-resistant strains. As early as 1991 it was
estimated that 50% of the bacteria responsible for a salmon disease called furunculosis in
Scotland were resistant to oxytetracycline (4). In British Columbia, strains of furunculosis
resistant to three approved antibiotics have been described since 1993 (5). In addition to bacteria
that cause specific diseases such as furunculosis, many other bacteria in the marine environment
in the vicinity of fish farms have been found to be resistant to antibiotics used on the farms (6,7).
Does this increase in antibiotic resistance in bacteria associated with farmed fish and their
marine environment lead to resistance in bacteria that cause disease in humans? Strong evidence
says yes, it does. Consider the following:
Several types of bacteria recovered from salmon or their marine environment can lead
to disease in humans (8, 9).
Resistant strains of bacteria causing animal disease can transfer their antibiotic
resistance to human bacteria (10,11)
One family of bacteria that are found in many places in nature, including both humans
and fish are enteric or gut bacteria. Among this family are various strains of E. Coli, Salmonella
and Serratia, which can leads to various diseases in humans, often resulting from is often the
consumption of meat that has been improperly processed or stored. Research indicates an
increase in antibiotic resistance in these types of bacteria worldwide.
In 1999, Alexandra Morton, a Vancouver Island biologist, caught a farmed salmon
shortly after an escape from a salmon farm. Samples from the salmon were sent for analysis. The
results showed that the salmon was infected with Serratia liquefaciens and Serratia plymuthia,
two enteric. Disturbingly, the bacteria showed resistance to 11 of the18 antibiotics tested on
them, including several antibiotics used to treat human diseases (9).
The Serratia family of bacteria is interesting in that, until recently, they were considered
relatively harmless to humans. In recent years it has also become clear that the Serratia bacteria
are opportunistic and can cause severe illness, such as respiratory and urinary tract infections, in
humans. The Serratia liquefaciens bacterium is responsible for 5 blood transfusion related deaths
in recent years in the U.S.A (10).
Transfer of antibiotic resistance.
In the above examples, antibiotic-resistant bacteria from fish can present a health hazard
to humans because these same bacteria also cause human diseases. But what of the other bacteria
associated with fish and their marine environment that develop resistance but are not directly
pathogenic to humans? These also represent a health risk because antibiotic resistant bacteria
have the ability to transfer that resistance to other bacteria that have never been exposed to
antibiotics. This is done through the transfer of a plasmid, a piece of genetic material, from the
strain of bacteria that has developed resistance to one that hasn't.
The problem of an increasing incidence of antibiotic resistant strains of bacteria is a
severe one, both in animal husbandry and in the treatment of human diseases. Many bacterial
infections in humans are proving difficult to treat with conventional antibiotics because of the
appearance of massive resistance. As we saw earlier, diseases that are a problem on fish farms
are also becoming more difficult to treat with conventional antibiotics. In the past, these two
areas of antibiotic use have been treated as separate. But can an increase in resistance among fish
diseases in the marine environment occur without any consequences for human health? A recent
study strongly suggests not. This research examined the distribution of oxytetracycline resistant
bacteria in aquaculture environments and in hospitals, and concluded that "the aquaculture and
human compartments of the environment behave as a single compartment" (12). In this
study, oxytetracycline resistant strains of Aeromonas bacteria were isolated from fish farms and
from hospital sewage. It was found that the plasmid, which genetically encoded the resistance in
the bacteria, was identical in bacteria from both environments. Furthermore, both the fish farm
and hospital bacteria were able to transfer that plasmid to strains of E. Coli, bacteria commonly
found in the intestines of humans. This study provided direct evidence, for the first time, "that
related tetracycline resistance-encoding plasmids have disseminated between different
Aeromonas species and E. Coli and between the human and aquaculture environments."
This transfer of antibiotic resistance through the free exchange of genetic material has
prompted researchers, such as professor Stuart B. Levy, director of the Centre for Adaptation
Genetics and Drug Resistance at the Tufts University School of Medicine, to state:
“The exchange of genes is so pervasive that the entire bacterial world can be
thought of as one huge multicellular organism in which the cells interchange their genes
with ease.”
Any measure increasing of antibiotic resistance for any bacteria, increases the genetic
reservoir of resistance available to all bacteria. Put another way, our capacity to treat human
diseases with antibiotics is a non-renewable resource. Every time we use antibiotics, we diminish
that capacity a bit more. If we use antibiotics other than for the treatment of human diseases, we
must be very careful that such use is urgently justified, and is managed impeccably. At present, it
seems clear that the use of these powerful drugs in fish farming is neither.
Nutritional Risks
Fat Content
The feed given to an animal and the conditions under which it is kept will influence the
animal’s composition. It is well known that wild land-based animals are leaner than their
domestic counterparts. Not surprisingly this is also the case for salmon. As early as the 1980’s,
Canadian consumer groups and health agencies expressed concern over the fat content of farmed
versus wild salmon. Not only is the fat content of farmed salmon higher than that of wild salmon,
but the composition of farmed salmon fat is less healthy than the that of wild salmon fat. Table 2
summarizes this.
The fats most strongly associated with human disease are saturated fats. Saturated fats are
available in many foods that we eat, primarily those of animal origin. The average North
American diet tends to supply much more saturated fats than the body needs. Saturated fats
contribute to heart attack, bowel cancer, gallbladder disease, and stroke. Poly-unsaturated, and
mono-unsaturated fats are far more healthful, especially the ones known as the essential fatty
acids (EFAs). The body cannot produce EFAs and we must get them from our diet.
These latter fats are divided up into omega-3 and omega-6 fatty acids. While both are needed,
health experts agree that it is important to consume foods that are ample in omega-3 fats, as these
confer many of the most desirable health benefits to humans. Excessive consumption of omega-6
fatty acids, on the other hand, can aggravate health problems. While omega-6 fats are widely
available from many sources, omega-3 fatty acids are more difficult to obtain; the best source is
from various types of seafood.
Table 2: Fat Composition comparison among various fish. Data obtained from the United States
Department of Agriculture nutrition database (12). Based on 100 gram serving of raw fish.
Type of fish
Total fat content
Omega-3 to omega-6
% of total fat that is
fatty acid ratio
omega-3 fatty acids.
Farmed Atlantic salmon 10.85
Wild Atlantic salmon
Farmed coho
Wild coho
Wild chinook
Wild chum salmon
Wild pink salmon
Wild sockeye
Wild mackerel
Wild anchovies
Table 1 compares the fatty acid composition for various types of fish. It can
be seen that farmed Atlantic salmon has 70% more fat than wild Atlantic salmon, and farmed
coho has 30% more fat than wild coho. Of specific interest to BC, however, is the comparison of
farmed Atlantic salmon (which accounts for 85% of farmed salmon production in BC) to the five
Pacific species of salmon. Farmed Atlantic salmon is about 200% higher in fat than wild pink or
chum salmon, 83% higher than wild coho, 27% higher than wild sockeye, and about the same in
total fat as wild chinook. It is also interesting to note that farmed Atlantic salmon has
significantly more fat than jack mackerel and anchovies, two of the species that are used to make
feed for farmed salmon.
If we now look at the last two columns in Table 1, which show the percentage of total fat that is
composed of omega-3 fatty acids, and the omega-3 to omega-6 ratio, the nutritional difference
among the different fish becomes even clearer. The highest percentage (32 to 33%) of omega-3
fats is found among wild pink salmon, anchovies, and wild Atlantic salmon. The group with the
second highest percentage range (20 to 25%) is wild coho, chum, and mackerel. The lowest
percentage (15 to 18%) of omega-3 fats is found among farmed Atlantic and farmed coho
salmon, as well as wild chinook and sockeye. Also, compared to Atlantic salmon, the other fish
in table 1, including chinook and sockeye salmon, have much higher omega-3 to omega-6 fat
ratios, an important factor for health considerations. For nutritional quality based on total fat,
percentage of omega-3 fats, and the omega-3 to omega-6 fat ratio, farmed Atlantic salmon is
the least desirable food source of all the above.
Net Loss of Seafood.
Salmon farming proponents often state that, since wild fisheries are collapsing all over
the Planet because of over-fishing, farming the oceans is necessary to feed a hungry world. They
claim that the fish farming industry can supply food while taking pressure off wild ocean
resources. This position is disingenuous and simplistic. The resource consumption of aquaculture
(the farming of a seafood species) varies, depending on what species is farmed and what method
is used. With regard to taking pressure off ocean resources, a key factor is whether the species
being farmed is carnivorous or not.
There are more than 250 different species of seafood currently farmed in the world and
about 85% of the total production is made up on non-carnivorous species. In British Columbia,
however, the majority of aquaculture production consists of salmon. Salmon are carnivores. In
order to try and mimic their natural diet, carnivorous species are given feed that is high in
fishmeal and fish oil. These key ingredients are obtained from wild fish such as sardines,
mackerel and anchovies, which are mainly supplied by South American wild fisheries.
From an ocean resource point of view, the total amount of wild fish used to make feed for
farmed salmon, compared to the total amount of salmon produced is of critical interest. But this
ratio is not recorded by the fish farm industry. Since feed is one of the most expensive
components of a salmon farm operation, fish farmers track the Feed Conversion Ration (FCR),
which is how much dry feed is used to make a given amount of salmon for market. The average
FCR for BC salmon farms is currently about 1.3 4 (1.3 tonnes of dry feed needed to make 1
tonne of fish for market). But this amount represents only a fraction of the weight of actual fish
used to make fish farm feed. The real question is: what weight of wild fish is needed to make that
1.3 tonnes of feed?
It is the fish oil component of salmon feed that consumes most of the wild fish used to
make that feed. Consequently, in order to obtain enough of this prized component, it is necessary
to use about 3 kilograms of wild fish to produce the 1.3 kilograms of fish feed. This in turn is
used to produce one kilogram of farmed salmon. Rather than taking pressure off ocean resources,
salmon farming is currently adding greatly to that pressure.
It takes 3 kilograms of wild fish to produce one kilogram of farmed salmon. As a result,
salmon farming results in a dramatic net loss of fisheries resources.
How did we get here? And how do we move on?
How did we get here?
This paper has outlined serious problems vis à vis human health, both local and shortterm, and widespread and long-term, associated with salmon farming as it is now practiced in
B.C. Not addressing these problems will result in the steady exacerbation of human health issues
on a number of fronts.
We believe that there are solutions to all the problems we have outlined. But first, we
would like to offer some brief comments on possible reasons why the current situation has
There is a fundamental conflict of interest inherent in the role of the CFIA (a conflict of
interest shared with other regulatory bodies). On the one hand responsible for monitoring the
Canadian food supply to ensure its safety and value, this CFIA is also mandated to promote sales
of Canadian food products and enhance the amount and dollar value of food sold.
It is impossible to serve two masters well, especially if their goals are in absolute conflict.
Let us furnish some examples.
There has been a long tradition of denial of the inter-relatedness of ecosystems, to some
extent within the scientific community and the citizenry at large, but today increasingly isolated
to parts of the commercial and regulatory sectors. Such a view is at odds with current, wellvalidated data, as we have shown above (11,12). But if a regulatory agency such as the CFIA has
a vested interest in promoting product sales, then its staff will be encouraged, at the level of
policy and operations, to ignore or downplay evidence of adverse ecological and human health
impacts of the industry it monitors.
Researchers at the University of Illinois have recently shown conclusively, using DNAamplification methods, that antibiotic resistance is created in bacteria in hogs. These bacteria
disperse from hog barns throughout streams and other surface waters (14). This is in accord with
the findings related to aquatic systems which we have noted above (11,12). If land and sea-based
farming operations spread antibiotic resistance, why would the CFIA not take decisive action to
address this issue? Why would containment of fish farm residues not be a sine qua non of
permitted technologies in B.C and throughout Canada?
The only explanation, we believe, is that the agency is unable to take human and
ecosystem safety concerns seriously because it is internally biased against these concerns when
they conflict with its other mandate, that of promoting and enhancing sales of Canadian food
products. Only thus can one explain the gross inadequacies in its monitoring activities, and its
acceptance of technologies that contribute to the generation of negative impacts. These include:
test results available only after food has been consumed;
an exceptionally incomplete pattern of monitoring;
inaction by the agency when confronted with stark scientific evidence of
burgeoning antibiotic resistance problems and transference of resistance to
human pathogens;
and most critically, the lack of serious discussion of the net loss of seafood
resources resulting from salmon farm feeding practices.
How do we move on?
Solutions exist for the current dilemmas in salmon farming outlined by this paper. Without being
exhaustive, they include:
1) Separating out the regulatory mandate of the CFIA from its mandate to promote
food sales and production. Whether this is done by creating a separate agency or
some other means, it is time for some agency to work solely for the protection of
human and ecosystem health (which are indissolubly linked) vis à vis the food
2) Converting the current open cage system to an exclusively closed system.
Currently there are pilot projects in progress to determine the viability of several
types of closed fish farm systems. These projects need to be expanded and properly
supported by both Federal and provincial governments.
3) A hard look at the issue of net loss of seafood resources. We believe a scientific
panel should be struck to examine this issue and give guidance to the industry and its
4) Widespread acknowledgement and promotion of the scientifically verified
principle of ecosystem interconnectedness. The source of much of the inadequate
regulatory actions and of the alarming passivity of the CFIA and other governmental
agencies arises from denial of this fundamental principle of living systems. What we
do to fish on fish farms, to hogs in hog barns, to soybeans in farmers’ fields, and to
ourselves in human communities, affects all other components of the one unified
Planetary ecosystem. To ignore this principle is to create conditions for future
generations that will make their lives straitened and impair their well-being in known
and unimaginable ways.
We do not believe it is our right to permit open-cage salmon farming, or any other
activity with disruptive effects on human and ecosystem health, to continue without correction.
We hope that this Commission will agree with us that drastic changes are needed, both short and
long-term, in the way salmon farming is conducted in this province and this country. We hope
that the Commission will not be swayed by rhetoric and unsubstantiated claims, but will focus on
scientific evidence and unequivocal documentation.
1) BC Environmental Assessment Office. 'Salmon Aquaculture Review', 1997, Volume 1, page 41.
2) Minister of Public Works and Government Services Canada. 'Health Canada Food Safety Assessment Program:
Assessment Report of the Canadian Food Inspection Agency Activities Related to the Safety of Aquaculture
Products'. June 2001. Available on the Health Canada Website at
3) EVS Environmental Consultants. In 'Impacts of Freshwater and Marine Aquaculture on the Environment:
Knowledge and Gaps (Preliminary Report). Prepared for Canadian Department of Fisheries and Oceans, June
2000, pp. 12.
4) Richards, R.H., et. al. Variations in antibiotic resistance patterns of Aeromonas salmonicida isolated from
Atlantic salmon (Salmo salar) in Scotland. In: C. Michel and D.J. Alderman (eds.). Chemotherapy in
aquaculture: from theory to reality. Symposium Paris, March 12-15, 1991. Office International des Epizooties,
Paris, France, pp. 276 - 287.
5) Ellis, D. and Associates. (1996). Net Loss: The Salmon Netcage Industry in British Columbia. A report to the
David Suzuki Foundation, pp. 107-108.
6) Lunestad, B.T. Fate and effects of antibacterial agents in aquatic environments. In: Chemotherapy in
aquaculture: from theory to reality. Symposium Paris, March 12-15, 1991. Office International des Epizooties,
Paris, France, pp. 152 - 161.
7) Smith, P.M., et. al. Bacterial resistance to antimicrobial agents used in fish farming; a critical evaluation of
method and meaning. Annual Review of Fish Diseases, Vol. 4: pp. 273 - 313, 1994.
8) Ellis, D. and Associates. (1996). Net Loss: The Salmon Netcage Industry in British Columbia. A report to the
David Suzuki Foundation, Appendix 14.
9) Morton, A. (1999). Lab report from Fish Pathology Lab, Ontario Veterinary College, University of Guelph,
submitted to Alexandra Morton, on the results of analysis of swab samples taken from an escaped Atlantic
salmon in the Broughton Archipelago, BC.
10) Roth, V. Blood product Contaminated with unusual bacteria. Presented at the Interscience Conference on
Antimicrobial Agents and Chemotherapy, September 26 - 29, 1999, San Francisco, California.
11) Midtvedt, T., et. al. Putative public health risks of antibiotic resistance development in aquatic bacteria. In:
Chemotherapy in aquaculture: from theory to reality. Symposium Paris, March 12-15, 1991. Office
International des Epizooties, Paris, France, pp. 302-314.
12) Rhodes, G., et. al. Distribution of oxytetracycline resistance plasmids between Aeromonads in hospital and
aquaculture environments: Implication of Tn1721 in dissemination of the tetracycline resistance determinant
Tet A. Applied and Environmental Microbiology, Vol. 66(9): pp. 3883 - 3890, Sept. 2000.
13) United States Department of Agriculture Database. Available at
14) ‘Conclusive link between hog mega-barns and antibiotic-resistant bacteria.” Union Farmer Monthly Vo52:5,
pg.7, August, 2001.