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Subject: Sea lice from wild salmon
From: "Salonius, Peter" <[log in to unmask]>
Reply-To:'Biology and control of sea lice"
Date:Tue, 4 Apr 2006 10:35:32 -0400

text/plain (118 lines)

With regard to "the probability of resistance being lower in the west due to the number
of [non resistant]sea lice coming into the area from returning wild salmonids", we can be sure that sea lice transfer is a two way street - from wild salmon to the farms (original source) - and later considerable transfer from farmed salmon to wild seaward migrating juvenile salmon, a transfer that in some areas in Norway occasionally infected over 90% of smolt as they passed aquaculture sites. 

So the avenue for the transfer of SLICE resistance(when and if resistance ocurrs) to the parasite population on wild salmon is ready and waiting.

Peter Salonius

-----Original Message-----
From: 'Biology and control of sea lice"
[mailto:[log in to unmask]]On Behalf Of Ross, Neil
Sent: Tuesday, April 04, 2006 10:59 AM
To: [log in to unmask]
Subject: Re: research on Sea lice resistance to Emamectin Benzoate

Forwarded on behalf of Dr. John Burka to keep discussion in public
-----Original Message-----
From: John Burka [mailto:[log in to unmask]]
Sent: Tuesday, March 28, 2006 2:48 PM
To: [log in to unmask]
Cc: Ross, Neil; [log in to unmask]; [log in to unmask]
Subject: Re: Re: research on Sea lice resistance to Emamectin Benzoate

Hi Kate:  The answer to your question is basically in any parasitology
textbook in sections on resistance to parasiticides.   Scientists at the
McGill University Institute of Parasitology have been working on
parasite resistance for years and are leaders in the field.  There is
always a bell curve with regards to resistance to a parasiticide.  The
more sensitive ones will be killed off and only the resistant ones will
survive.  If, eventually, there are only resistant parasites left, and
no parasites from outside replenish the population, then the resistant
population will dominate ... however they could be still be sensitive to
a parasiticide with another mechanism of action and be controlled.  Thus
the need for alternate drugs!  That is why we have suggested that there
be more drugs than avermectins available to control sea lice.  If sea
lice from outside populations reinfest the fish, the resistant
populations are diluted and control can be maintained.  In Atlantic
Canada, the wild salmon population is low and thus the number of sea
lice repopulation would be low ... unless they are coming from another
source than Atlantic salmon.  However, despite the theoretical higher
probability for resistance development in Atlantic Canada, none has
developed.  Thus SLICE is therapeutically effective.  In BC, there is a
huge wild salmon population (compared to eastern Canada) and thus
providing sufficient new sea lice to dilute any resistant pool.  There
could also be other sources of sea lice than salmon, such as
sticklebacks, as has been shown by Simon Jones.  I don't know where you
are getting your data that there are few leps in the wild population in
BC, as Todd's study has shown them to have been in the Pacific for
thousands, if not millions of years (Canadian Journal of Fisheries and
Aquatic Sciences 61, 2004, 1176-1190).  They did not just appear there
with the advent of fish farming.  

Thus, resistance to SLICE is not occurring in no jurisdiction where it
is used.  This may mean that it is an extremely effective drug or that
the whole process of resistance development is even more complicated
than we now know it.  

I hope this answers your question.  Cheers,  John

-----Original Message-----
From: "Kate Pinsonneault" <[log in to unmask]>
To: <[log in to unmask]>
Date: Tue, 28 Mar 2006 10:13:46 -0800
Subject: Re: research on Sea lice resistance to Emamectin Benzoate

Hi John,
Thanks for your prompt reply.  I was interested in your information re
the probability of resistance being lower in the west due to the number
of sea lice coming into the area from returning wild salmonids.  I
wonder if you could provide me with a lead to the research  on this.  I
am very curious as my understanding is that the sea lice on the
returning salmon is primarily caligus while the sea lice that are most
prevalent on the farms are predominantly lep's.  I would be very
interested in finding out more about this.  Any information you could
provide or leads to studies on this would be very much appreciated.
Kind regards,
----- Original Message -----
From: "John Burka" <[log in to unmask]>
To: <[log in to unmask]>
Cc: <[log in to unmask]>
Sent: Monday, March 27, 2006 3:25 PM
Subject: Re: research on Sea lice resistance to Emamectin Benzoate

> Hi Kate:  Not that I know of.  Just for your information, the 
> probability of incidence to emamectin benzoate occuring on the west 
> coast is very much lower than on the east coast due to the high number

> of sea lice coming in to farms from wild samonids, i.e. a high refugia

> population. Hope this information is useful.  Cheers,  John
> -----Original Message-----
> From: Kate Pinsonneault <[log in to unmask]>
> To: [log in to unmask]
> Date: Mon, 27 Mar 2006 14:27:25 -0800
> Subject: research on Sea lice resistance to Emamectin Benzoate
> Hi,
>    I have recently been asked whether there is any research being done

> on sea lice resistance to Emamectin Benzoate (Slice) here on the west
> Please let me know if you are aware of any studies underway.
> Thanks,
> Kate
> Kate Pinsonneault
> Stewardship Coordinator
> Broughton Archipelago Stewardship Society

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