Report of the 2005 ICES/NASCO Symposium on Interactions ...

NINA SPECIAL REPORT 34
heavy infestations <strong>of</strong> largely juvenile stages <strong>of</strong> sea lice. We
undertook laboratory-based infestation <strong>of</strong> wild sea trout
smolts with Lepeoph<strong>the</strong>irus salmonis, in order to determine
<strong>the</strong> threshold levels <strong>of</strong> sea lice which induce sub-lethal
physiological stress and osmoregulatory dysfunction. In a
parallel series <strong>of</strong> experiments for sea-lice infested postsmolt
sea trout, we also examined <strong>the</strong> physiological
consequences <strong>of</strong> premature return to fresh water. The
osmoregulatory ability and status <strong>of</strong> <strong>the</strong>se fish was
assessed by a variety <strong>of</strong> physiological, biochemical and
histological techniques including branchial, intestinal and
renal Na + K + -ATPase activity, plasma ion composition, and
drinking rate. Stress was assessed by determination <strong>of</strong>
plasma levels <strong>of</strong> cortisol, MSH, glucose and lactate and
liver glycogen levels. In addition, <strong>the</strong> integrity <strong>of</strong> skin and
gill tissue was assessed by SEM,TEM and confocal laser
scanning microscopy. This suite <strong>of</strong> analytical techniques
has allowed us to estimate <strong>the</strong> sea lice infestation levels
that trigger sub-lethal, chronic and acute physiological
stress in sea trout.
Survival and growth <strong>of</strong> sea-ranched Atlantic
salmon treated against salmon lice prior to
release
Ove T Skilbrei and Vidar Wennevik
Smolts were treated with SLICE ® (orally administered
emamectin benzoate) prior to releases in <strong>the</strong> River Dale,
western Norway, to study <strong>the</strong> potential effects <strong>of</strong> salmon
lice during <strong>the</strong> early stay in <strong>the</strong> sea. A total <strong>of</strong> 10,470
treated and control fish <strong>of</strong> 10 family groups were adipose
fin-clipped, micro-tagged, and released in <strong>the</strong> Dale River
on three different dates in 2002: May 11, May 25 and June
7, in accordance with <strong>the</strong> timing <strong>of</strong> <strong>the</strong> natural smolt run.
Grilse returns in 2003 did not differ between <strong>the</strong> treated
and control group smolts released in May 2002, but <strong>the</strong>
grilse returns from <strong>the</strong> treated smolts released on 7 June
2002 were almost twice those derived from <strong>the</strong>
untreated control group. The weights <strong>of</strong> <strong>the</strong> grilse
generally declined from <strong>the</strong> first to <strong>the</strong> third release date,
and <strong>the</strong> treated fish were approximately 15 % heavier
than <strong>the</strong> controls. The higher return rate <strong>of</strong> smolts
treated and released on June 7 was also observed for <strong>the</strong>
2-sea-winter salmon in 2004. We conclude that <strong>the</strong>
infestation level <strong>of</strong> salmon lice changed from non-lethal to
lethal levels during <strong>the</strong> period <strong>of</strong> <strong>the</strong> smolt migration, and
that non-lethal infestation levels may considerably affect
Atlantic salmon by reducing growth rate and spawning
size.
Exceptional production <strong>of</strong> pink salmon in
2003/2004 indicates that farmed salmon
and wild Pacific salmon can coexist
successfully in a marine ecosystem on <strong>the</strong>
Pacific coast <strong>of</strong> Canada
Richard J Beamish, Simon Jones, Chrys-Ellen Neville, Ruston
Sweeting, Grace Kareman, Sonja Saksida and Elysha Gordon
Juvenile pink salmon that entered <strong>the</strong> marine waters in a
marine ecosystem along <strong>the</strong> eastern margin <strong>of</strong> Queen
Charlotte Strait in 2003 and returned as adults in 2004
had very high marine survival. The early seaward
migration and mid-summer rearing in 2003 was in an area
containing 16 active Atlantic salmon farms. Two species <strong>of</strong>
sea lice were commonly found on farmed salmon and
wild salmon. The exceptional marine survival <strong>of</strong> pink
salmon indicates that pink salmon populations and farmed
salmon coexisted successfully in 2003.
Susceptibility to <strong>the</strong> sea louse
(Lepeoph<strong>the</strong>irus salmonis), Infectious
Salmon Anemia and Furunculosis among
salmon <strong>of</strong> wild, farmed and hybrid
parentage
Kevin A Glover
Genetic differences between Atlantic salmon <strong>of</strong> wild and
farmed backgrounds have been observed for a variety <strong>of</strong>
biological, behavioural and life-history traits. Notably,
several authors have demonstrated that salmon <strong>of</strong> farmed
parentage display reduced survival in natural ecosystems
compared to <strong>the</strong> <strong>of</strong>fspring <strong>of</strong> wild parentage. Despite
<strong>the</strong>se key differences however, at present, potential
differences in susceptibility to disease have been little
explored. Susceptibility to disease represents an
important aspect <strong>of</strong> fitness under both domestic and
natural environments. It is also conceivable that genetic
differences in susceptibility to disease may exist between
salmon <strong>of</strong> farmed and wild parentage due to <strong>the</strong> different
selection regimes <strong>the</strong>y are exposed to in <strong>the</strong>ir respective
environments. Here, we summarise <strong>the</strong> results <strong>of</strong> four
studies where salmon <strong>of</strong> wild, farmed and hybrid
backgrounds have been compared in <strong>the</strong>ir susceptibility to
<strong>the</strong> sea louse (Lepeoph<strong>the</strong>irus salmonis), Infectious Salmon
Anemia and Furunculosis. Toge<strong>the</strong>r, results from <strong>the</strong>se
studies indicate that large and systematic differences in
susceptibility to disease are unlikely to exist among salmon
<strong>of</strong> farmed and wild parentage. It is recommended,
however, that this topic deserves fur<strong>the</strong>r investigation.
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