by Craig Weatherby
A few weeks ago, we reported on efforts by Canadian biologists to block the threat of viral disease in farmed salmon, and its spread to wild salmon and other wild fish.
As we wrote then, “Salmon farms from Norway, Scotland, and Chile to Eastern Canada have all suffered outbreaks of a viral disease called Infectious Salmon Anemia (ISA).”
Even the generally pro-farming trade publication IntraFish worried in print that ISA will spread to the many offshore salmon farms located in British Columbia, to BC’s wild salmon and other wild fish.
This threat to wild fish was highlighted by the escape late last year of 43,000 farmed salmon from a pen located near British Columbia’s Klemtu region.
Today brought word of yet another of many worldwide outbreaks—some approaching a million fish—this time on an industrial salmon farm sited near Scotland’s Shetland Islands.
Farms may breed greater viral virulence and frequency
The ISA virus is natural to wild salmon, and farmed salmon can get it from nearby wild salmon... or, and this is key, from the hatchery eggs from which all farmed salmon are born (Nylund A et al. 2007; Vike S et al. 2008).
The ISA in wild salmon usually occurs in benign forms that produce no symptoms.
Instead, the fears for wild salmon stem from virulent strains that can occur in the wild, but do little harm, probably because of the generally very low density of wild fish per square mile.
Salmon farms seem to serve as effective incubators and reservoirs, and may help virulent strains develop due to the very high density of fish accelerating the speed of viral transmission and mutation.
Transmission of the virus from farmed salmon to wild Pacific Salmon has yet to be documented, because ISA has not yet appeared in Canadian farms.
If ISA appears on Canadian salmon farms and spreads to wild Pacific salmon, the extent of its damage to wild stocks could become apparent too late.
We recently published a letter from marine biologist Alexandra Morton to Premier Gordon Campbell of British Columbia. See “Farmed Salmon Virus Threatens Wild Pacific Salmon.”
And we thought you’d be interested to see the literally incredible response to that letter, which Ms. Morton received from Canada’s Ministry of Fisheries and Oceans, rather than Mr. Campbell.
Why does this dispute matter to US consumers? Americans purchase some 80 percent of the farmed salmon produced in British Columbia’s offshore waters, many located too near to migratory rivers for the health and safety of wild salmon (See “Canada’s Wild Salmon Need Americans' Help”).
Alexandra Morton’s Response to Premier Gordon Campbell
This is the letter Alexandra Morton wrote back to Premier Campbell, pointing out the barefaced untruth and evasion contained in the Ministry’s response to her warning against the threat of ISA infections on British Columbian salmon farms:
Dear Premier Campbell:As you indicated I have now received a response from DFO to my letter regarding the global spread of the fish farm virus Infectious Salmon Anemia (ISA).Infectious Salmon Anemia is a highly contagious, rapid-mutating, flu-like virus following the salmon farming industry around the world. When the industry’s own publication IntraFish wrote: “How Long Can BC Avoid ISA? (Jan. 12) I wrote to you requesting the BC border be closed to farm salmon livestock imports.I don’t think you understand the enormity of the ISA threat and clearly neither does Mr. Thompson, Regional Director /Fisheries and Aquaculture Branch DFO.In his email he assured me there are measures in place to protect BC from ISA because, “The ISA virus is not transmitted vertically (i.e. from adult to eggs/embryos),” suggesting the fish farming industry can continuing importing livestock in the form of eggs.Please note the following scientific paper:ISA virus in Chile: evidence of vertical transmission (Vike et al 2008, Arch. Virol. 2009). “…. the best explanation for the Norwegian ISA virus in Chile is transmission via embryos, i.e. vertical or transgenerational transmission. This supports other studies showing that the ISA virus can be transmitted vertically” (Vike S et al. 2008).Premier Campbell, DFO’s assurances are meaningless if they are not keeping up with the science and do not understand how this virus spreads. As such BC fisheries are entirely at risk. What can you possibly be thinking to risk Canada’s North Pacific herring, halibut, salmon and trout stocks with an imported virus as virulent as ISA?Premier Campbell you are responsible for salmon farming in British Columbia. What are you going to do? Leave the border open to the virus or close it?Alexandra Morton
Recent findings on ISA
Four years ago, Norwegian scientists proposed some hypotheses about how wild and farmed salmon interact with regard to ISA.
The following excerpts come from “Emergence and maintenance of infectious salmon anaemia virus (ISAV) in Europe: a new hypothesis” (Nylund A et al. 2003):
Based on existing information about infectious salmon anaemia (ISA) and new information emerging from the present study, it is hypothesized that:
- ISAV is maintained in wild populations of trout and salmon in Europe
- It is transmitted between wild hosts mainly during their freshwater spawning phase in rivers
- Wild salmonids, mainly trout, possibly carry benign wild-type ISAV isolates
- A change (mutation) in virulence probably results from deletions of amino acid segments from the highly polymorphic region (HPR) of benign wild-type isolates
- ISA emerges in farmed Atlantic salmon when mutated isolates are transmitted from wild salmonids or, following mutation of benign isolates, in farmed salmon after transmission from wild salmonids
- Farming activity is an important factor in transmission of ISAV between farming sites in addition to transmission of ISAV from wild salmonids to farmed salmon
- Transmission of ISAV from farmed to wild salmonids probably occurs less frequently than transmission from wild to farmed fish due to lower frequency of susceptible wild individuals
- The frequency of new outbreaks of ISA in farmed salmon probably reflects natural variation in the prevalence of ISAV in wild populations of salmonids
- Craig N. Deadly ISA fish disease hits Scotland. Accessed online Feburary 1, 2009 at http://www.practicalfishkeeping.co.uk/pfk/pages/item.php?news=1948
- DiPietro B. How Long can B.C. Avoid ISA? Intrafish.com. January 12, 2009. Accessed online at http://www.intrafish.no/global/news/article237546.ece
- Ely B. Infectious Salmon Anaemia. National Institute for Medical Research. Accessed online January 12, 2009 at http://www.nimr.mrc.ac.uk/MillHillEssays/1999/isa.htm
- Morton A. Email communication received February 2, 2009.
- Morton A. Email communication received January 12, 2009.
- Nylund A, Devold M, Plarre H, Isdal E, Aarseth M. Emergence and maintenance of infectious salmon anaemia virus (ISAV) in Europe: a new hypothesis. Dis Aquat Organ. 2003 Aug 15;56(1):11-24.
- Nylund A, Plarre H, Karlsen M, Fridell F, Ottem KF, Bratland A, Saether PA. Transmission of infectious salmon anaemia virus (ISAV) in farmed populations of Atlantic salmon (Salmo salar). Arch Virol. 2007 Jan;152(1):151-79. Epub 2006 Aug 28.
- Plarre H, Devold M, Snow M, Nylund A. Prevalence of infectious salmon anaemia virus (ISAV) in wild salmonids in western Norway. Dis Aquat Organ. 2005 Aug 9;66(1):71-9.
- USDA Animal and Plant Health Inspection Service. Infectious Salmon Anemia, Canada, November, 1999: Impact Worksheet Update. Accessed online January 12, 2009 at http://www.aphis.usda.gov/vs/ceah/cei/taf/iw_1999_files/foreign/isacanadaupd.htm
- USDA Animal and Plant Health Inspection Service. Infectious Salmon Anemia: January 2002. Accessed online January 12, 2009 at http://www.aphis.usda.gov/lpa/pubs/tnisa.html
- Vike S, Nylund S, Nylund A. ISA virus in Chile: evidence of vertical transmission. Arch Virol. 2009;154(1):1-8. Epub 2008 Nov 26.