The physiological and ecological
effects of salmon lice infection
on anadromous salmonids.
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By
Bengt Finstad (NINA) and Pål Arne Bjørn (FF)
Wild sea trout infected by salmon lice
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Wild sea trout infected by salmon lice
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Life cycle of salmon lice
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nauplius
copepodid
chalimus
adult male
preadult male
preadult female
adult female
Aims (1993-1998)
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• To test the survival time of salmon lice through a delousing
process on fish in fresh water
• To describe the development, distribution on the host and
pathogenicity of salmon lice on sea trout
• To test the physiological effect of salmon lice on sea trout
and Atlantic salmon post smolts
• To describe the salmon lice infection on wild Atlantic
salmon, sea trout and Arctic char post smolts in areas with
and without salmon farming activity, and consider possible
effects of the infection.
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Salmon lice registrations in Norway
Survival of salmon lice on Arctic char in freshwater
Total number of salmon lice on fish
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250
200
150
100
50
0
0
28 56
84
112 140 168 196 224 252 280 308
Time (hours)
504
Conclusions
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(Finstad et al., 1995. Aquaculture Research, 26:791-795)
• 60% of the salmon lice survived one week in freshwater.
• Salmon lice may survive for up to three weeks in
freshwater.
• The delousing process was a continuos one.
• The results imply that attached lice could maintain their
salt balance by feeding on the host, and this may damage
the host even during delousing in freshwater.
Development of salmon lice
100
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Day 7, n=20
60
Frequency (%)
20
100
Day 14, n=20
60
20
100
Day 19, n=20
60
20
100
Day 24, n=20
60
20
100
Day 29, n=20
60
20
100
Day 38, n=20
60
20
CH1 CH3 P1M P1F P2M P2F ADM ADF
Developmental stages
Conclusions
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(Bjørn and Finstad, 1998. Can. J. of Zool. 76: 970-977)
• Male lice developed faster than female lice, taking 29 and
38 days, respectively, to reach the adult stage, but less than
40% of the lice reach the adult stage.
• The chalimus larvae preferred the gills and the fins,
especially the dorsal fin, and caused minor skin damages.
• Preadult and adult lice stages preferred the head and dorsal
areas of the fish, and caused severe skin damages.
• Salmon lice seem to have more or less the same
developmental rates, distribution on the host and
pathogenicity as seen in Atlantic salmon.
Mortality in lice infected sea trout post smolts
Accumulated mortality (n)
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30
25
20
15
10
5
0
1
7
14
19
24
Days post infection
29
38
Relative density of lice on sea trout post smolts
Relative density (lice/fish weight)
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3.0
2.5
infected
2.0
moribund
1.5
1.0
0.5
0
7
14
19
22-25
26-29
Days post infection
30-38
Plasma cortisol concentration in sea trout post smolts
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Cortisol (nmol/l)
800
400
200
infected
100
control
0
7
14
19
24
Days post infection
29
38
Plasma chloride concentration in sea trout post smolts
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Chloride (mmol/l)
260
240
infected
220
control
200
180
moribund
160
140
120
7
14
19
22-25
Days post infection
26-29 30-38
Conclusions
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(Bjørn and Finstad, 1998. Nord. J. of Freshw.
Res. 73: 60-72; Finstad et al., 2000. Aquac. Res. 31: 795-803)
• Heavy salmon lice infections causes a stress response in
salmonids, even at chalimus stages of the lice.
• Chalimus stages, however, causes only minor
osmoregulatory disturbances to the fish.
• Preadult and adult stages of the lice causes severe
osmoregulatory problems to the host, thereby leading to
mortality with high infection.
• The results on Atlantic salmon and sea trout post smolts,
imply that a relative infection of 0.75 and 1.6 lice larvae
per gram fish weight, respectively, can be suggested.
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Wounds on wild sea trout caused by salmon lice
Field sampling techniques
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Experimental design
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• Atlantic salmon post
smolt were captured by a
pelagic par-trawl.
• Different zones of
Trondheimsfjorden were
trawled annually in
May/June 1992 to 1998.
• Salmon lice number
and developmental
stages on the fish were
counted.
N
Zone 6
Zone
5
Zone 4 Zone
3
Zone
2
Zone
1
Trondheim
Salmon lice infection intensity
Year Zone Prevalence Mean
>10 lice (%)
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1992
1993
1994
1995
1996
1997
1998
1
3
1
2
3
4
5
3
6
2
3
4
1
2
3
1
2
3
5
6
2
3
0
54
0
0
1.5
0
0
12
46
0
4
19
25
29
26
1
4
5
5
11
44
53
4.8
8
1
2.6
1.6
1
2.6
1.5
4.9
2.2
1.2
1.5
2
1.3
22
7.2
0.9
3.4
0.3
11.1
11.8
Conclusions
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(Finstad et al., 2000. Aquac. Res. 31: 795-803).
• Atlantic salmon post smolt may become infected with
salmon lice during fjord migration.
• The migrating post smolts were only infected with
chalimus stages, and the infection level was generally low.
• However, in some years, the infection level was higher,
and indicated that salmon lice may be a possible cause of
Atlantic salmon post smolt mortality.
Experimental design
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• Sea trout and Arctic char
were captured in June, July,
August and September
1997 at the exposed (Vik)
and the unexposed area
(Bogen).
• Fish were gill-netted in
the sea and sampled by
electrofishing in freshwater.
• At the exposed locality,
sea trout captured both in
sea and in freshwater were
in addition blood sampled.
Vik
Harstad
Bogen
Narvik
Exposed locality
Sampling week
Hab
n
Prev
mean min
max
SW
FW
SW
FW
SW
FW
FW
SW
27
12
27
11
14
19
1
3
89
76
96
91
93
95
100
33
Hab
n
Prev
mean
min
max
SW
FW
SW
FW
SW
FW
SW
FW
21
3
11
2
9
0
16
1
61.9
0
54.5
0
88.9
1
1
4
6
1
13
6
2
12
68.8
100
13
1
36
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26
29
32
37
123
133
203
206
53
45
6
8
11
1
10
1
0.3
1
445
279
471
532
101
160
13
1
Unexposed locality
Sampling week
26
29
32
37
Plasma cortisol level in wild sea trout post smolts
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Cortisol (nmol/l)
500
400
300
Habitat
200
100
SW
0
FW
N=
5 14
6 2
7 12
low
medium
high
Relative intensity (lice/fish weight)
Salmon lice density on wild sea trout post smolt
Relative density (lice/fish weight)
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10
8
6
Habitat
4
2
SW
0
FW
N=
24 9
26
26 10
29
Week
13 18
1 1
32
37
Conclusions
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(Bjørn et al., 2001. Aquac. Res. 32: 947-962.
• The salmon lice infection is very high in the exposed area,
and heavily infected sea trout tended to return prematurely
to freshwater.
• The salmon lice infection is low in the unexposed area, and
few sea trouts were captured in freshwater.
• Heavy salmon lice infection caused a stress response in
wild sea trout, and 30-50% of the fish from the exposed
locality is expected to suffer from physiological
disturbances or mortality because of the infection.
• Salmon lice may, therefore, have the potential to cause
mortality of sea trout, and with time, may even render the
population at the risk of eradication.
Experimental design
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• Sea trout and Arctic char were captured
in sympatry at sea in June, July and August
1992 and 1993 at the exposed (Alta) and
the unexposed area (Lille Porsanger).
• Number of lice and developmental stages
on the hosts were counted in the
laboratory.
Altafjorden
Laksefjorden
Lille Porsanger
River Hals
Exposed system
Unexposed system
Salmon lice abundance of all stages
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Altafjorden 1992
Sampling week
26
29
32
n
Prev
mean
min max
40
30
20
7.1
80.0
65.0
0.1
23.6
12.1
0
0
0
3
97
74
13
22
28
15.4
77.3
75.0
0.2
4.4
13.0
0
0
0
1
24
84
42
31
77
0
12.9
94.8
0.3
19.9
0
7
0 134
5
20
40
0
10.0
82.5
0.2
3.9
Laksefjorden 1992
26
29
32
Altafjorden 1993
25
28
31
Laksefjorden 1993
25
28
31
0
0
3
21
Conclusions
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(Bjørn and Finstad, 2002. ICES. J. of Mar. Sci. 59: 131-139)
• The salmon lice infection differed significantly between
the exposed and unexposed area on both species.
• The salmon lice infection also differed within and between
years.
• The infection pattern in the exposed area showed an
epidemic tendency.
• The results imply that salmon lice epidemics may also
occur on Arctic char in the northernmost area of Norway.
Summary
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• Salmon lice were able to survive for up to 3 weeks in
freshwater.
• Adult males developed faster than adult females. Fourty
percent survival up to adult stages were observed. Mobile
stages caused severe skin damage.
• Physiological studies showed that a relative density of
0.75 and 1.6 lice per gram fish weight led to mortality.
Severe stress responses were also monitored.
Summary (cont.)
Fiskeriforskning
• Salmon lice infection may cause mortality of fjord
migrating Atlantic salmon post smolt in some years,
although the infections mostly were low.
• The salmon lice infection were, however, significantly
higher in an exposed compared to an unexposed locality in
Nordland county, and may affect the population severely.
• The same tendency was also found at an exposed locality
in Finnmark, and both Arctic char and sea trout seem to be
susceptible to infections.
• Considering some of these results, salmon lice must at
present be regarded as a major threat to wild populations of
salmonids in some areas of intensive fish farming activity.
Fiskeriforskning
New results (1999-2001), future
strategies og research needs
• Increased research and monitoring of salmon lice
on farmed and wild salmonids.
• Epidemiological studies and risks of infestation.
• Strategies
Monitoring of sea trout and Arctic charr;
examples from 2000.
Number of lice on wild salmonids
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60
13
50
40
9
30
14
12
10
20
1
11
8
10
3
2
47
5
6
15
0
-10
-10
0
10
20
30
40
Exposure index for farmed salmon
50
60
70
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Monitoring in bag nets - coast/fjord
Monitoring of salmon lice on returning wild- and
farmed Atlantic
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1997
Locality Type
N
Large
Female
Total
W
92
5±9
5±3
9±6
18 ± 16
E
81
11 ± 18
6±5
12 ± 8
28 ± 24
W
18
64 ± 190
7±8
5±6
76 ± 192
E
104
130 ± 241
8 ± 11
6±6
145 ± 247
Large
Female
Total
Coast
Fjord
Larvae
1998
Locality Type
Coast
Fjord
N
Larvae
W
59
1±4
2±3
9±9
13 ± 11
E
58
7 ± 39
3±4
7±7
16 ± 39
W
26
32 ± 100
4±4
9±8
46 ± 102
E
219
39 ± 112
3±5
2±6
43 ± 115
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•
Salmon lice - wild/farmed fish
Average costs to produce 600 000 kg salmon* in 20 net pens á 10 000
salmon (Mustafa et al. 2001, Can. Vet. J. 42). * smoltprice Can$2.00.
1. Farm without
sea lice problem
2. Farm with sea
lice problem (no
treatment)
3. Farm with sea lice
problem (regular treatment)
Can$ 3 600 000
Can$ 3 936 000
Can$ 3 696 000a
Can$ 3 678 000b
Can$ 3 708 000c
1-2=
Can$ 339 000
1-3=
Can$ 96 000
Can$ 78 000
Can$ 108 000
a
Azamethipos
Hydrogenperoksyd
c
Teflubenzuron
b
Meta project 2002-2005
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NRC salmon
programme
Growth and survival
of Atlantic salmon
National monitoring
Escaped salmon and
salmon lice
Geographic
Duration of residence in
fjords
EU, NINA & NRC
Migratory routes
Infestation studies
Migratory routes
Laboratory studies
Modelling sites for
“safe”
establishment of
fish farms
Modelling wind and water
currents
NRC salmon
programme
Spread of salmon
lice
Water quality in freshwater
FHF & NRC
Water quality and
smolts
Migratory models
Geographic variations
AquaNet, NINA &
Statkraft
Migratory routes
Risk of infestation