A newsletter on the biology and control of sea lice distributed free to researchers,aquaculture and fisheries industry, educators, consultants, and managementauthorities.
This fifth issue of
4th International Conference on Sea Lice
28th-30th June 1998, Trinity College, Dublin, Ireland
The 3rd international conference held in Amsterdam in 1998 focused on
sea lice biology. This meeting will thus focus on applied aspects of
• progress and future options for vaccines
• Integrated Lice Management strategies
• lice population dynamics, including production, dispersal,
transmission between farms and between farms and wild fish.
Submission of abstracts
A limited number of rooms has been booked in good quality
accomodation in Trinity College, Dublin. This is the most convenientplace to stay for the conference, is in the city centre and is half the
price of hotels and guesthouses. When these rooms are full, delegates
will have to make their own arrangements for accommodation. Rooms
will only be reserved for named persons on payment of costs.
Reports and News
*All rooms have access to a kitchen if people want to make their own
Offers of papers must be submitted by 26th February 1999. Final
versions of abstracts are required by 31st March 1999. All peoplepresenting papers must pre-pay their registration fee.
Standard guidelines for the presentation of posters and talks and
Wrasse – do they transfer diseases to salmon?
Department of Fisheries and Marine Biology, University of Bergen, Norway
Being in close contact with salmon in netpens, feeding partly from their mucus layer or on lice filledwith salmon blood, as well as on the carcasses of dead salmon, wrasse would be likely to contractpathogens present in the salmon population. Given the wrasses ability to escape from salmon pens,diseases could be spread to wild wrasse populations, or to new salmon farms with subsequent capture ofescaped wrasse.
Likewise the possibility of introducing new pathogens to salmon farming, by stocking wild wrasse
with an unknown history of disease, has been a concern of the salmon farming industry. In some areasthis has hindered the commercial use of wrasse as delousers.
This article summarizes the results from a three-year project on wrasse health, including screening of
wild wrasse populations, the role of wrasse as a vector for diseases, and the prevention and treatment ofdiseases in wrasse. The goldsinny (Ctenolabrus rupestris)
was chosen as a model, as it is the speciesmost frequently used as a delouser in salmon farms.
DISEASES OF WILD WRASSE
A goldsinny population from the western part of
Only parasites with a direct life cycle, which
Norway was sampled every second month from
might be transferred from wrasse to salmon
February to November. Simultaneously fish from
potential problem in salmon farming. In this
transferred to a salmon farm was sampled. For
each population and sample date 30 fish were
trichodinids on the gills of the goldsinny. The
examined immediately after transfer to the
trichodinids did not cause any pathogenicity, even
laboratory, and another 30 were put into a latent
in the most heavily infected goldsinnys, and
carrier test. The goldsinny was screened for
seemed to be species specific for wrasse. The
presence of bacterial diseases, IPN-virus and
screening of the parasite fauna was done as a
Solberg (Dept. of Fisheries and Marine Biology,
goldsinny gave no cytopatic effect on CHSE-
WRASSE AS A POSSIBLE VECTOR OF
cells. The CHSE-cells, however, will only
sustain growth of a limited number of viruses, so
Infectious Salmon Anemia (ISA)
the presence of “new” viruses in goldsinny can
This viral disease causes mortality and clinical
not be ruled out by this screening. There is no
signs of disease mainly in farmed Atlantic salmon
evidence from the literature that wild wrasse
but sea trout (Salmo trutta)
carry viruses, but experiments have shown that
(Nylund and Jacobsen, 1995),
goldsinny are susceptible to IPNV (Gibson and
(Nylund et al., 1997) and
herring (Clupea harengus)
have proved to be asymptomatic carriers with the
Examination of freshly caught goldsinny from the
ability to transfer ISA to healthy salmon. To
wild revealed no external or internal signs of
either confirm or rule out the wrasse as a possible
bacterial diseases, and pathogenic bacteria could
not be isolated from the kidney. After the Latent
Carrier test the picture was completely altered. In
Blood from salmon positive for ISA, from natural
one particular sample a maximum of 33 % of the
outbreaks and from earlier transmission trials,
goldsinny were found to have covert infections of
an atypical Aeromonas salmonicida
while the common incidence was 6-10%.
2 x 30 goldsinny cohabiting with 5 ISA-injected
Atypical and classical furunculosis
As wild wrasse may carry an atypical variant of
2 x 30 salmon cohabiting with 5 ISA-injected
it is of great importance
to find out if this bacteria may be transmitted to,
30 goldsinny injected with HBSS (negative
and cause disease in, salmon. Earlier work have
demonstrated that wrasse are susceptible to
30 untreated salmon kept with 5 untreated
classical furunculosis from salmon, both in
laboratory experiments (Bricknell et al., 1996)
30 salmon injected with ISA (positive control).
and in a farming situation (Hjeltnes et al., 1992).
From all treatment groups, and from goldsinny
In a laboratory experiment, groups of 2 x 30
negative control, five fish were taken out for
goldsinny wrasse and Atlantic salmon were
examination every fifth day from day five until
intraperitonally injected with “high”
day forty after infection. Moribund fish were
(107CFU/fish) and “low” (105CFU/fish) doses of
taken out for examination on a daily basis. All
fish were examined externally and internally for
salmon or atypical Aeromonas salmonicida
clinical signs of disease. Blood samples were
taken for determination of hematocrit. Tissue
In salmon injected with a “low” dose of
samples from several organs was fixed for
examination in light and electron microscope, and
mortality started at day three and reached 100 %
frozen for later immunohistology. From the ISA-
within day eight post-injection. In the salmon
injected goldsinny blood and tissue was frozen
groups injected with the atypical variant there
for later re-infection experiments with salmon.
was no mortality, and sequential examination of
While mortality started on day 17 and ceased
fish showed no signs of disease. The experiment
on day 28 (90% mortality) in the ISA injected
gave no indications that the atypical furunculosis
salmon, there were no mortality in the goldsinny
from wrasse could be transmitted to salmon,
injected with ISA, in goldsinny cohabiting with
which corresponds to the findings of Costello et
injected salmon, or in salmon cohabiting with
injected goldsinny. Neither were there any
In the goldsinny groups injected with “high
clinical signs of disease or drop in hematocrit in
doses” the mortalities for both isolates reached
these groups. Samples of tissue processed for
about 80 % within 15 days. In thewhile in the
light microscopy or for immunohistology did not
“low dose” groups mortalities were a bit higher in
show any signs of tissue damage, or positive
the atypical group (45 %) than in the classical
reaction for the presence of ISA Virus.
group (35 %). When given an intraperitoneal
In the re-infection experiment blood and tissue
taken from the ISA-injected goldsinny (day 5, 10,
susceptible to classical furunculosis from salmon
15, 20, 25, 30, 35 and 40) was prepared and
as to atypical furunculosis from wrasse. This
intraperitoneal injected into eight groups of
implies that under farming situations with
healthy salmon. There were no mortality in any
classical furunculosis present in the salmon
groups of salmon, neither clinical signs of disease
population the use of goldsinny as cleaner fish
or drop in hematocrit in salmon sampled from
should be avoided, because of the risk of
these groups. In a positive control group of
mortalities in the wrasse and spreading the
The conclusion from the experiments must be
Prevention and treatment of atypical
that it is highly unlikely that goldsinny will be
furunculosis in wrasse
able to transfer ISA to or between salmon groups
under natural conditions. The virus does not
Preliminary trials with vaccination of freshly
seem to be able to establish an infection in
caught goldsinny in April-May demonstrated the
goldsinny, and through the cohabitation trials the
problems with vaccinating a carrier population.
role of goldsinny as a possible passive vector
The stress of handling was sufficient to cause an
At present all material from the experimental
goldsinny, and from 400 fish ip injected with an
groups, frozen and stored in liquid nitrogen, are
commercial oil-based triple-vaccine only 50%
being screened by the use of PCR, to examine
survived the five-week long immunization period.
clearance rate and possible traces of ISA- virus inthe samples.
A following challenge with atypical and classical
furunculosis proved to be rather inconclusive.
chemotherapeutics to wild-caught goldsinny via
the oral route, but even though ip. injection is
vaccinated in December with an oil-based trial
quite labor-intensive it will reduce the amount of
vaccine made of formaldehyde-killed atypical
antibiotics used and thereby spare both costs and
bacteria. As goldsinny
are scarcely available in early spring, when the
100,000 smolts using 5,000 goldsinny (1: 20) will
salmon smolts are put to sea, trials with winter-
need 250 ml Aquacycline ¨ vet., or 12.5 g
storage of goldsinny have been conducted.
Oxytetracycline. Further investigation will
Simultaneous vaccination would give several
probably show that the dose could be further
advantages with the possibility of disease
outbreaks being lower during the winter months,
lower social interactions between the goldsinny,
The screening of a goldsinny population from the
and a much longer immunization period (5-6
pathogens that should pose an threat to salmon
reaction caused by low water temperatures.
farming, neither were the goldsinny able to
transmit ISA or atypical furunculosis to salmon.
promising results as mortalities in vaccinated
The main problem seems to be the mortality in
group receiving subsequent handling-stress was
the goldsinny, caused by stress-induced outbreaks
significantly lower than in unvaccinated groups.
of atypical furunculosis, after transfer to netpens.
Challenge experiments with ip injection of
This disease may be treated efficaciously by
atypical Aeromonas salmonicida
injection of Oxytetracycline. Vaccination of
to demonstrate any effect of vaccination, but this
goldsinny is difficult when the population
method for challenge may be unsuitable.
contains carriers with covert infections, but
Treatment with antibiotics
vaccination combined with winter-storage has
Given the high mortality caused by stress-induced
outbreaks of atypical furunculosis and the
difficulties in vaccinating the fish, a more
Bricknell, I.R., Bruno, D.W. and Stone, J., 1996. Aeromonas
applicable approach to reduce mortality could be
infectivity studies in goldsinny wrasse,Ctenolabrus rupestris
. Journal of Fish Diseases, 19: 469-
treatment with antibiotics. An experiment using
three different antibiotics to treat a natural
Costello, M., Deady, S., Pike, A. and Fives, J., 1994.
outbreak of atypical furunculosis was therefore
Parasites and diseases of wrasse (Labridae) being used as
conducted in the laboratory. Three antibiotics
cleaner-fish on salmon farms in Ireland and Scotland. In
were chosen on the basis of sensitivity studies of
Wrasse –Biology and use in Aquaculture, Sayer, M.D.J.,Treasurer, J.W. Costello, M.J. (Eds.), pp: 211 –
Gibson, D.R. and Sommerville, C., 1996. The potential for
caused by atypical furunculosis started. For each
viral problems related to the use of wrasse (Labridae) in
treatment 2x55 fish was used. Fish in two groups
the farming of Atlantic salmon. In Wrasse –Biology anduse in Aquaculture (Sayer, M.D.J., Treasurer, J.W. and
were ip. injected with 0.5 ml Tribrissen ¨vet. (400
Costello, M.J., eds.), pp: 240 - 246. Oxford: Fishing
mg/ml Sulfadiazine – 80 mg/ml Trimethoprim),
and two with 0.5 ml Aquacycline ¨ vet. (50 mg/ml
Hjeltnes, B., Bergh, O., Holm, J.C. and Wergeland, H.,
Oxytetracycline). Two groups were bath treated
1995. The possibility of transmission of furunculosis
with Flumequine (0.5 g/l) for three hours, and
from farmed salmon to marine fish. Diseases of AquaticOrganisms, 23: 25-31.
two groups kept as control. Dead and moribund
Nylund, A. and Jacobsen, P., 1995. Sea trout as a carrier of
infectious salmon anaemia virus. Journal of Fish
At the termination of the experiment, 28 days
after treatment, the cumulative mortality was 47.5
Nylund, A., Kvenseth, A.M., Kross¿y, B. and Hodneland,
% both in control groups and Tribrissen injected
K., 1997. Replication of the infectios salmon anaemiavirus (ISAV) in rainbow trout, Oncorhynchus mykiss
(Walbaum). Journal of Fish Diseases, 20: 275-27
mortality reached 34% while in the Aquacyclin-treated groups mortality was only 14%.
Summary of the Irish sea trout problem
Salmon Research Agency, Co. Mayo, Ireland
This article was circulated on the sealice e-mail discussion group in August 1998
In reply to those requests for information on the
sea trout collapse in the west of Ireland and
whether sea lice were the cause of the collapse, it
was clear from the uninformed statements and
ordinated a broadly based research programme
questions that have appeared recently on e-mail
which, it was hoped, would identify the extent of
that it is necessary to restate the problem and
the problem and define a possible cause or causes.
where it has occurred. There is a substantial body
of published reports and papers which are
implicating sea lice as the major component of the
collapse, are summarised in Whelan (1992).
During the following two years the research
species, there has been increasing evidence during
programme concentrated on five principal areas:
the past two decades of a slow decline in some
• Monitoring of sea trout survival in a range of
stocks and this was largely attributed to poaching
with fine mesh monofilament and a range of
• Further investigations into the role of sea lice
environmental problems such as: field drainage,stream drainage and maintenance fertilization of
• A physiological profile of sea trout smolts to
the hillsides, afforestation and more recently
study their state of fitness when entering
hillside erosion, due to overgrazing by sheep
Whelan (1991, 1992, 1993) and Poole et al
• The development of practical sea trout
(1996), described the appearance of a more
serious decline which appeared in many fisheries
In 1991 the Department of the Marine established
along the western seaboard in 1986 which, by
a Sea Trout Working Group and the results of the
1989, resulted in a population collapse in most
sea trout research programme were examined by
mid-western sea trout fisheries. Subsequent
this group at the end of each year (Anon, 1991,
research programmes (Anon 1990, 1992, 1993,
1992, 1993, 1994). The "sea trout problem" in
1994) confirmed that the declining rod catches
the Irish context was defined as the following:
reflected an actual spawning stock collapse,approximately 90-98% reduction in ova
deposition rates in one catchment studied.
severe infestations of juvenile (chalimus)stages of lice, Lepeophtheirus salmonis
The major collapse occurred in 1989 when,
the presence of larger badly emaciated fish
tragically, there was little sea trout research
a severe reduction in spawning stock, across
taking place and only some anecdotal information
is available on the sequence of events which tookplace during the May/June period of 1989.
However, the following details are known:
The most severe collapse in sea trout stock
levels occurred in the area from Clew Bay in
some mending kelts appeared in the estuaries
the north to Galway Bay in the south.
Of the 60+ rivers sampled around the coast of
Ireland between 1991 and 1996, no exception
has been found to the observation that the sea
available showing the level of lice damage
trout problem, as defined above, has been
to the skin and fins of the more seriously
recorded only in areas where salmon farming
In some fisheries, appreciable numbers of
• No evidence of a disease was found which
In the latter half of the 1980's, farm salmon
was consistent with the stock collapse. A
production in the bays of the mid-west of Ireland
range of internal parasites were identified but
expanded to an unprecedented extent. Sea lice
none that provided an explanation for the
consequence juvenile lice production soared. No
Holland & Poole 1993; Anon. 1991).
observed data exist for juvenile lice production
• There was no evidence of sea trout feeding
during this period but extrapolation from the lice
regularly in the vicinity of cages, where it was
production figures indicates the massive release
claimed pollack and coalfish were eating the
of larvae which took place at this time. It has also
fish, or that sea trout smolts were straying
been shown that increasing sea temperatures in
the late 1980's were directly linked with faster
• From the stomachs of the sea fish caught,
generation times in the louse life cycle (Tully &
while sampling for sea trout, there was no
evidence of reduced food availability at sea or
a lack of specific food items (e.g. sandeels).
shown; the sea trout smolts, and adults where
The collapse in the elver (young eel) stocks
present, are consistently infested by juvenile lice
and predation by seals were also discounted.
and that in the mid-west of Ireland during 1991,
• While acid flushes or chronic acidification
95% of the total nauplius larval production of
, the louse causing the
problem, was of fish farm origin. It has also been
direct evidence to identify a causal link.
shown that sea trout were infested with juvenile
lice within two to three weeks of migrating to sea
environmental changes have taken place and
and that morphological and physiological impact
these undoubtedly affect stocks in specific
of the lice on the trout was sufficient to cause
catchments. The sea trout stock collapse,
correlations have also been found between both
individually or collectively to these changes.
abundance and intensity of lice on sea trout with
• No global failure of osmoregulatory ability of
distance from neighbouring fish farms. While
sea trout, which could explain the premature
these correlations are by their very nature
return of sea trout smolts to rivers, was
relatively crude, they have provided the impetus
for further detailed in-bay research into themechanisms governing sea lice infestation from
The only consistent factors to emerge from the
research carried out to date are the early return of
In 1996 the Salmon Research Agency attended
both smolts and kelts to the estuaries in early to
the ICES Working Group in Edinburgh and the
main conclusions of this group were as follows:
infestations of juvenile salmon lice (Anon. 1991,
• Highest numbers of lice on wild sea trout
1993a, 1993b, 1994; Tully & Whelan 1993, Tully
post-smolts in Ireland, Scotland and Norway
. 1993a, Tully et al
. 1993b). The sea trout
comparable levels of infestation have not
observed in areas adjacent to intensive salmon
been recorded outside farming areas (also
farming. The problem is therefore geographically
note ref. Tingley et al
. 1997, ICES J. Mar.
distinct and any valid hypothesis must be able to
• The phenomenon of sea lice related early
returning sea trout post-smolts and related
promoted as having been involved but results to
date, particularly the high survival rates of
stocked parr, would indicate that it is a marine
• In Norway, sea trout post-smolts do not return
based mortality of trout and no common factor, or
early except where they are infested with sea
suite of factors, have been identified as having
lice. These infestations are dominated by
caused the sea trout stock collapses in the west of
juvenile stages, as also observed in Scotland
Ireland. The "building of dams, roads, gravel
digging, silage etc" (Kvenseth, Caligus 20/7/98)
do not have any connection with the current sea
It is now known that salmon lice cause stress,
trout situation in the west of Ireland.
mortality to host fish such as sea trout, salmon
Poole, W.R., Whelan, K.F., Dillane, M.G., Cooke, D.J. and
Matthews, M. 1996. The performance of sea trout,
l., stocks from the Burrishoole system
western Ireland, 1970-1994. Fisheries Management &
infestation on early returns of sea trout post-
Poole, W.R. & Whelan, K.F. (1996). The sea trout stock in
salmon lice significantly shorten sea trout's
the Burrishoole catchment and a review of the symptoms
of the west of Ireland sea trout collapse. Paper presented
to: ICES Workshop on the Interactions between Salmon
Data relating to the proximity of fish farms
Lice and Salmonids, ICES CM 1997/M:4.
and the lice infestations in sea trout from
Tully. O., 1991. Assessment of the impact of sea lice
Scotland indicate that a similar correlation to
) infestation on sea trout smolts
Ireland may have been present in 1994 - the
on the west coast of Ireland during 1990 and 1991. The
only year considered in detail by the ICES
Salmon Research Agency of Ireland Inc. Internal Report.
Tully, O., Poole, W.R. and Whelan, K.F. 1993a. Infestation
• The data suggest that lice emanating from fish
parameters for Lepeophtheirus salmonis
farms may transfer to wild trout populations
(Copepoda:Caligidae) parasitic on sea trout (Salmo trutta
but this has as yet not been quantified.
L) post smolts on the west coast of Ireland during 1990
and 1991. Aquaculture and Fisheries Management, 24
Tully, O., Poole, W.R. and Whelan K.F. and Merigoux
• The scarcity of wild salmonids inshore in
1993b. Parameters and possible causes of epizootics of
(Kroyer) parasitic on sea trout
February to April reduces the possibility that
L) on the west coast of Ireland.
Proceedings of the First European Crustacea Conference.
the spring pulse of larval lice was derived
Paris, August 31 - September 5, 1992 Pathogens of wild
from wild sea going salmonids present at or
and Farmed Fish, Sea Lice
(ed. by G.A. Boxshall). Ellis
Tully, O. and Mulloy, S. 1993c. Infestation of sea trout
The commisioned report examining the 1992 -
L.) by the salmon louse (Lepeophtheirus
1996 sea trout sampling programme, undertaken
(Kroyer) in Ireland during 1993. ICES CM
by Dr Ian Cowx, identified a number of perceived
and actual inaccuracies in the programme. These
Tully, O., Gargan, P. and Whelan, K.F. 1993d. Infestation
were fully addressed in the 1997 programme. The
of sea trout (Salmo trutta
L.) by sea lice (Lepeophtheirus
inaccuracies identified were found to have not
(Kroyer)) in systems close to and distant fromsalmon farms in Ireland. ICES CM 1993/M:56.
significantly altered either the database or the
Tully, O. and Whelan, K.F. 1993e. Production of nauplii of
conclusions drawn from it and the 1997 modified
programme completely corroborated the 1992-
from farmed and wild Atlantic salmon (Salmo salar
the west coast of Ireland during 1991 and its relation to
Hopefully this description of the current status
infestation levels on wild sea trout (Salmo trutta
Fisheries Research 17. 187-200.
Whelan, K.F. 1991. Disappearing sea trout - decline or
population collapses in the west of Ireland will
collapse? The Salmon Net No. 23. 24-31.
help to inform those looking for such information.
Whelan, K.F. 1992. Management of salmon and sea trout
stocks. Environment and Development in Ireland.
Proceedings of a Conference held at University College
Anon., 1990. Declining sea trout stocks in the Galway /
Dublin. The Environmental Institute, University college
south Mayo region - A scientific appraisal. The Salmon
Research Agency of Ireland Inc. Internal Report.
Whelan, K.F. 1993. Historic overview of the sea trout
collapse in the west of Ireland. In: Aquaculture in
Anon., 1991-94. Reports of the Sea Trout Working Group.
Ireland - towards sustainability. Ed. J. Meldon.
Fisheries Research Centre, Department of the Marine,
Proceedings of a Conference held at Furbo, Co. Galway.
30th April - 1 May. 1993. 51-53. An Taisce, Dublin.
Mulloy, S., Holland, C. and Poole, R. 1993. Helminth
Whelan, K.F. 1993. Decline of sea trout in the west of
parasites of brown and sea trout Salmo trutta
L. from the
Ireland: an indication of forthcoming marine problems
west coast of Ireland. Biology and Environment: Proc.
for salmon? Proceedings of the Fourth International
Roy. Ir. Acad., Vol. 93b no. 3. 137-142.
Atlantic Salmon Symposium, St. Andrews, N.B. Canada,
Murphy, T., Drinnan, E.H., Poole, W.R. and Whelan, K.F.
June 1992. Salmon in the Sea and New Enhancement
1993. Histological and virological investigations into the
- (Ed. D. Mills) Fishing News Books, Chapter
collapse of sea trout populations in the west coast of
Sea lice management methods in Scotland
Marine Harvest McConnell, Lochailort, Inverness-shire PH38 4LZ, U.K.
This paper was presented at the workshop on sea lice control on fish farms in Trondheim, November1997.
(a) sea lice infestation patterns on farms in Scotland investigating whether the source of infection isexternal or is generated from within the farms;
(b) factors governing infestation cycles and the pattern of infection;
(c) methods to prevent and treat sea lice and
(d) the choice of medicine, the timing of the treatment and how frequently the fish should be treated.
Internal or external infection patterns?
sites and it is difficult to conclude whetherCaligus
are an increasing problem. Annual
Smolts (1992 year class) stocked on a production
fluctuations in settlement of Caligus
farm in west Scotland with one sea winter
were evident on a farm in Loch Sunart over four
production fish already present (1991 year class)
year classes (Fig 2). Treatment with Aquagard-
were rapidly infected with Lepeophtheirus
Novartis (dichlorvos 50% w/v) is normally very
and copepodids were found on the
effective in removing Caligus,
and there is no
newly stocked fish within 3 days (Fig. 1). Up to 8
indication of reduced sensitivity to this
mobile L. salmonis
were recorded 4 weeks after
stocking and the fish were treated with Aquagard(dichlorvos) at regular intervals through the first
In farms that have been fallowed the recruitment
summer. In the following year the farm was
of lice in late spring in the second year is a
fallowed for several weeks and this subsequent
critical period in sea lice control (Fig. 3). In this
year class remained relatively uninfested with lice
example there was an initial infestation with
through the first year and only one treatment with
and this declined naturally without
Aquagard was required during this period. In
many farms where fallowing is applied, lice
numbers of chalimi of L. salmonis
treatment is not required for up to 15 months
rapidly followed by a rise in weeks 18 to 20 of
following transfer to sea and this treatment can be
mobile L. salmonis
to an average of 12 per fish.
then solely for Caligus elongatus
rather than L.
At this point fish were treated with Aquagard.
. This was also the conclusion from an
One further treatment was required at the
intensive study of four Scottish salmon farms that
beginning of August. The increase in lice
established that recruitment of lice was initially
slow following fallowing and emanated from
logarithmic. Several factors may be involved in
wild fish (Bron et al., 1993). Thereafter the build
this rapid increase in sea lice infestation in weeks
up of lice was largely internally generated within
16-20, including increasing day length, rising
water temperatures and increasing salinity(allowing greater larval survival). In addition,
The pattern of infestation with Caligus
copepodids may be less viable in winter due to
well established direct route of transfer from wild
smaller egg size and a reduced nutrient reserve,
although larger numbers of smaller eggs are
therefore fallowing has little effect on controlling
produced. In late spring fewer larger eggs are
this species. Caligus
numbers on salmon often
produced, and larger eggs may give more viable
decline naturally with the onset of colder weather
in November or an influx of freshwater. Therecruitment of Caligus
varies greatly between
Estuarine plankton are adapted to prevent wash
been used to give protection in cages. On one
out including mechanisms for vertical movement
farm used as an example (Fig. 5) smolts were
in seawater. Nauplii and copepodids of sea lice
stocked with larger fish, as this was a broodstock
are likely to behave in the same way as other
site. In 1994 smolts were treated with Aquagard
zooplankton. Bron et al. (1993) indicated the
on three occasions but no treatment was required
average survival time of copepodids at 10°C as 7
in 1995 after wrasse were stocked on a group of 8
days but it could be as much as 21 days in a farm
situation in a confined bay area. Two tides each
Wrasse have been found to be less effective in
day, each with flow and ebb movements, provides
the second year of the production cycle. I have
four opportunities per day for copepodids to pass
carried out a trials with larger corkwing wrasse
through a farm. Over a week this is 28 occasions,
on 2 cages but with little effect. An alternative
and over 3 weeks 84 opportunities. Together with
would be to try ballan wrasse as good results
high egg production this can explain the rapid
using ballan have been reported from Norway.
increase in lice numbers from a relatively small
Ballan are relatively uncommon in Scotland
(Treasurer, 1996b), about 1% of the catch, and
Lice control methods in Scotland
culture of ballan would be required.
Part of the ineffectiveness of wrasse in the
management is being followed and this may
second year is the disappearance of wrasse over
the first winter. Special hides have been
companies in certain sea loch areas.
developed by Martin Sayer of the DunstaffnageMarine laboratory, Oban providing a buffer to
sudden changes in salinity and temperature.
These have been trialled on farms but with no
companies operating in Loch Sunart included
conclusive results; although survival of wrasse
specifying a fallow period, on stocking a single
improved, they continued to be lost from the
year class, and on exchanging information on the
cages. Wrasse were not found dead and therefore
health of the fish. Prior to this, in the 1989 year
it was assumed that they have escaped through
class, lice infested fish rapidly following stocking
and remained high through the production cycle
Another problem has been the occurrence of an
(Fig. 4). The first treatment with Aquagard was in
atypical furunculosis, Aeromonas salmonicida
September of the first year and a total of 22
wrasse following capture, transfer and stocking in
treatments was required in this year class. In 1991
cages. Wrasse should be vaccinated although the
when a fallow period of 8 weeks was used,
induction period is too short and there would
numbers of L. salmonis
were low through the first
year with only Caligus
present in any numbers
and not sufficiently high to require treatment. Itwas 15 months before the first treatment was
required. Fallowing was therefore very effective
There are only three licensed medicines for
with a 50% reduction in the number of treatments
treatment of salmon infested with sea lice in
compared with the 1991 year class. The option to
Scotland. Dichlorvos (Aquagard-Novartis) as 1
fallow may not be available to small companies
ppm active is applied as a bath treatment with the
who have a limited number of farms or only one
cage enclosed with a tarpaulin. The discharge of
farm and where fish of various sizes are required
this medicine is regulated by the Scottish
Environmental Protection Agency and the volume
of dichlorvos that can be discharged has beenreduced in many cases in line with the Paris
In 1994 a questionnaire was sent to fish farming
Convention 1974 for the protection of the North
companies in Scotland asking about their use of
wrasse (Treasurer, 1996a). Wrasse were stocked
requirement to reduce the use of various toxic
widely with the smolt input, 150,000 wrasse in
and persistent chemicals including dichlorvos.
1994 representing 33% of farms and 39% of fish
put to sea that year. Wrasse have been effective
available to treat a farm once per annum. Also
in the first year of the production cycle where
many lice populations are resistant to the use of
wrasse have been treated carefully and hides have
LEGEND FOR FIGURESFig. 1. Comparison of numbers of mobile L. salmonis
in 1991 on a farm in west Scotland with mixed yearclasses with 1992 after fallowing (single year class). Arrows indicate dates of treatment in 1991. Time is shownas the weeks of the year (i.e. 1-52 from January to December).
Fig. 2. Mean numbers of mobile Caligus elongatus
in the first year of the production cycle in 1991, 1993, 1995and 1997Fig. 3. A typical pattern of infestation with L. salmonis
showing the increase in lice numbers in the second year.
The reduction in numbers corresponds to 2 treatments with Aquagard.
Fig. 4. Comparison of numbers of mobile L. salmonis
in 1989 when there was no management agreement with1991 when the sea loch system was fallowed.
Fig. 5. Comparison of numbers of L. salmonis
in 1995 when wrasse were stocked with 1994.
Fig. 6. An example of the efficacy of hydrogen peroxide as a treatment for sea lice in spring of the second year ofthe production cycle. Arrows indicate treatment dates.
Fig. 7. A comparison of chalimus numbers in 1996 on a farm in west Scotland following 3 winter treatments(treatment dates indicated with an arrow) with 1994 when this policy was not applied.
Fig. 8. A comparison of numbers of mobile L. salmonis
following winter treatments (compare Fig. 7).
this organophosphate, particularly at lower water
medicine has to have a marketing authorisation in
temperatures, and treatments can be ineffective
(Jones et al
. 1992). Azamethiphos (Salmosan,
authorisation are submitted to the Veterinary
Novartis) has recently been granted a marketing
Medicines Directorate (VMD) and are assessed
authorisation and discharge consents have been
on the quality, efficacy and safety of the product.
The VMD is advised by the independentVeterinary Products Committee. Obtaining a
The third medicine is hydrogen peroxide,
supplied as Paramove by Solvay Interox and
consuming and expensive process, e.g.
Salartect by Brenntag. This is also applied as a
azamethiphos took 6 years from the beginning of
bath treatment and can be very effective (Fig. 6).
the Animal Test Certificate (ATC) trials.
Although up to 80% of lice recovered fromtreated cages were active after an hour (Treasurer
Un-licensed medicines can be prescribed by a
& Grant, 1997), there have been no reported
veterinarian where treatment is necessary on
cases of significant resettlement on salmon. The
main problem with hydrogen peroxide is toxicity
alternatives are considered as being ineffective.
at water temperatures in excess of 14°C. In
The veterinarian makes a series of decisions
addition, chalimi are unaffected, effectiveness
against mobile lice may not be complete, and egg
In addition, the medicine has to be granted a
bearing females are more difficult to remove.
discharge consent by the Scottish Environmental
These medicines are both applied as a bath
Protection Agency (SEPA). Under section 23 of
treatment and there can be variations in enclosed
the Water Act 1989 fish farms are classified as
volume compared with target volume. When the
trade premises and any wastes are classified as
tarpaulin has not been filled adequately a higher
trade effluent and require a discharge consent.
more toxic concentration is achieved and with a
An application for a consent has to made for each
large fill the target concentration is not attained,
individual farm and depending on the size of the
farm extensive hydrographic data are required to
applications are labour intensive, may stress fish,
predict the scale of discharge that can be made
and licensed medicines do not kill the larval
without breaching short term Environmental
stages. Furthermore, the appetite of fish is
Quality Standards. An application for a discharge
frequently affected by treatment and fish are
consent is advertised in the local press.
starved on the day before and during treatment.
Following extensive laboratory and field trialsand environmental impact studies, SEPA gave alimited issue of restrictive consents for
ivermectin for a trial period. Efficacy has been
Within the terms of the Medicines Act 1968, any
good but there have been political issues in
substance intended to be used as a veterinary
national strategy was launched by the Scottish
Pharmaceuticals) has been trialled under an
Animal Test Certificate and this medicine will
planned sealice treatments throughout designated
shortly receive a marketing authorisation. The
areas in spring to coincide with the time of year
product is very effective against mobile and to a
when copepodid survival has been shown to be
lesser extent larval stages. Discharge consents
lowest (Wadsworth et al., 1998). The results of
the strategy have not been published but havebeen reported to be favourable and further
No in-feed treatment is licensed (but see
improvement will be possible if more effective
ivermectin), although three possibilities have
medicines such as cypermethrin are more widely
been used in limited trials under ATC. Onions
and garlic have been tried in bags and in feed butwere ineffective. Neither have light luresdemonstrated efficacy.
The development of a successful vaccine is notimminent. While immune stimulants have given
Bron, J. E., Sommerville, C., Wootten, R. & Rae, G.
good laboratory results (Simon Wadsworth, pers.
(1993). Fallowing of marine Atlantic salmon,
comm.), they have not been found to be effective
L. farms as a method for the control of
sea lice, Lepeophtheirus salmonis
Journal of Fish Diseases 16, 487-493.
Immediate assistance would be the provision ofother more effective medicines but at present the
Jones, M.W., Sommerville, C. & Wootten, R. (1992).
most effective use of current medicines must be
Reduced sensitivity of the salmon louse,
considered, particularly hydrogen peroxide. This
to the organophosphate
involves strategic or winter treatments; treating
dichlorvos. Journal of Fish Diseases 15, 197-202.
fish when sea lice numbers are low and stable at
Ritchie, G., Mordue, A.J., Pike, A.W. & Rae, G.H.
the beginning of the year. Ritchie et al. (1993)
(1993). The reproductive output of Lepeophtheirus
showed that many small eggs are produced at this
adult females in relation to seasonal
time and survival of copepodids is poor because
variability of temperature and photoperiod. In :
of a low nutrient reserve. In an example from
Pathogens of wild and farmed fish: sea lice.
Boxshall, G.A. & Defaye, D. Ellis Horwood,
Loch Sunart fish were treated with hydrogen
peroxide on 3 occasions from March atapproximately 6 weekly intervals, weeks 10, 17
Treasurer, J.W. (1996a). Wrasse (Labridae) as cleaner-
and 23 (Fig. 7). This had the effect of reducing
fish of sea lice on farmed Atlantic salmon in west
the spring increase in sea lice numbers. A
Scotland. In: Wrasse: biology and use inaquaculture. Sayer, M.D.J., Treasurer, J.W. &
comparison is made of the 1993 with the 1995
Costello, M.J. Fishing News Books, Oxford, 185-
year class in the second year of the production
cycle. Chalimus numbers in 1996 weresignificantly less (ANOVA on log transformed
Treasurer, J.W. (1996b). Capture techniques for
data, P<0.05), 5.5 on average compared with 21.8
wrasse in inshore waters of west Scotland. In:Wrasse: biology and use in aquaculture. Sayer,
in 1994 (Fig. 7). Numbers of mobile L. salmonis
M.D.J., Treasurer, J.W. & Costello, M.J. Fishing
were also less, 13.4 weekly average for the
second year compared with 31.1 in 1994 (Fig 8).
The number of treatments in the second year was
Treasurer, J.W. & Grant, A. (1997). The efficacy of
reduced by up to 46%, the length of time between
hydrogen peroxide for the treatment of farmedAtlantic salmon, Salmo salar
L. infested with sea
treatments was extended, damage to fish was
lice (Copepoda: Caligidae). Aquaculture 148, 265-
reduced, there were fewer mortalities and
improved fish quality (Wadsworth et al
Wadsworth, S., Grant, A. & Treasurer, J.W. (1998). A
This policy and procedure should be allied to
strategic approach to lice control. Fish Farmer 21
coordinating treatments between farms in a
prescribed area and followed up with subsequenttreatments based on a lice surveillance system.
The availability of more effective medicines willenhance the success of this initiative. Recently a
Vaccine against salmon lice
Dr Rob Raynard
FRS, Marine Laboratory, Victoria Road, PO Box 101, Aberdeen AB11 9DB, Scotland, U.K.
Summary of a project funded under the EC FAIR Research programme: AIR2-CT93-1079
The immune system of fish, as in human, reacts against invading foreign substances. Faced with adisease, the immune system will try to eliminate the infectious agent or substance, for example infectiousbacteria, as soon as it has been identified. However, the infection may be too advanced by the time theimmune system is fully reacting. Vaccines can accelerate this process. During vaccination, specificportions of the infectious agent (antigens) are injected to stimulate a specific reaction of the immunesystem (build up of antibodies) to prevent recurrence of the disease. The risk of infection is limited, asonly antigens and not the disease agent are injected. During future infections, the immune system willreact quicker to the already known disease and consequently improve the chances of survival of theanimal.
This common method of vaccination can not be developed against lice as only the exoskeleton and mouthparts of the lice are in contact with the fish. The immune system does not recognise any foreignsubstances in the blood stream and the active defence mechanisms are not being triggered. However, licefeed on skin and mucus of salmon and thereby take blood meals. As the antibody, which recognise thetarget, and the white cells, which destroy it, are present in the blood, it was suggested that fish mightfight against lice externally through the action of their blood’s defence mechanisms ingested by the lice.
Indeed, if the immune system is prepared to react against gut cells of lice, it will be triggered within thelice gut and against it. Therefore, lice could be eradicated by the action of the fish immune systemfollowing a blood meal. Such vaccination techniques have been used to fight bloodsucker parasites ofcows and sheep.
The partners of this project managed to design several vaccines aimed to be used as described above.
However, tests on salmon challenged with lice showed only a limited efficacy of the vaccination. Severalreasons may explain this poor success. Firstly, lice, unlike bloodsuckers, only ingest a limited amount ofblood. Secondly, there is still room for some improvements of the vaccine. Nevertheless, this newapproach for treatment of parasites in fish is of great interest and research efforts are being continued toimprove the present vaccine. Further development may be expected in a near future.
Cloning and characterisation of Lepeophtheirus salmonis microsatellite genetic elements as useful
tools for the study of sea lice ecology.
Brief description of project
A two-year research project funded under the Operational Programme for Fisheries (1994-1999) andadministered by the Marine Institute (Dublin) seeks to develop DNA profiling techniques and examinetheir usefulness in improving our knowledge of the ecology of the sea louse Lepeophtheirus salmonis
The method being developed is based on examining repetitive DNA elements termed microsatellites, andis used in conjunction with the polymerase chain reaction (PCR) allowing the genetic profile ofindividual sea-lice to be determined. This type of DNA fingerprinting has proved useful in the researchof other species including areas such as identity testing, pedigree analysis, disease diagnosis, andpopulation genetics. Once described, the DNA profiling tools will be tested and assessed for theirability to detect genetic variation in sea-lice recovered from both farmed and wild fish. The researchaim is to describe the genetic variation within identified single populations of L. salmonis
and alsobetween different populations of L. salmonis
The work is being conducted by Dr Richard Powell (Department of Microbiology) and Dr Sam Martin,(National Diagnostics Centre, BioResearch Ireland) of the National University of Ireland, Galway. Theyare currently at the half-way mark, and have cloned and determined the DNA sequence of forty sea-licemicrosatellites, and developed ten microsatellite-PCR assays. The final year of the project will now bespent examining whether these new DNA profiling tests have the potential to provide new informationon the monitoring and movement of sea-lice populations.
Semiochemicals for sea lice control
Zoology Department, Aberdeen University, Tillydrone Avenue, Aberdeen AB24 2TZ.
Semiochemicals are naturally occurring chemicals
As a result of these studies, we now have
unequivocal evidence that male and female salmon
organisms. Some of these compounds have been
lice exhibit behavioural responses to a variety of
exploited in order to regulate insect behaviour. For
fish-derived stimuli, and that the molecules
example, sex pheromones are used to lure, trap
involved are quite stable in seawater. These
and disrupt the behaviour of some moth pests1 and
responses are directional and kinetic, and provide
the compounds that attract some veterinary pests
the first evidence that L. salmonis
to their mammalian hosts have also been used in
positive rheotaxis to fish-conditioned water.
traps2. Such approaches now form important
semiochemical sources elicit the greatest attractant
response, we will extract the organic components
The theory, methodologies and technologies
that have given rise to such strategies are now
electrophysiological techniques to record the
being applied to the problem of Lepeophtheirus
sensory responses of lice to these compounds. The
. We are in the process of identifying the
aim of this is to show a clear relationship between
semiochemicals which attract salmon lice to their
hosts and male lice to their mates*. It has long
chemoreceptors and the triggering of host-finding
been suggested that parasitic copepods use fish-
behaviour. At this point we can embark on
derived odours, at least in part, to identify their
detailed studies of the particular molecules
hosts3,4 and preliminary work has shown that lice
eliciting this chain of events. It is these we hope to
do have a behavioural response to these stimuli5.
investigate for their potential in trapping and
The successful identification of such compounds
will allow us to investigate the possibilities ofdesigning lice traps or of creating disruptive
*Link Aquaculture (SAL 11). Aberdeen University - AJ
Mordue, AW Pike, W Mordue; Nottingham University - I
Currently, our research focuses on host-finding
Duce; IACR-Rothamsted - JA Pickett, L Wadhams. Fundedby Natural Environment Research Council, the Scottish
behaviour by adult lice. Significant numbers of
Salmon Growers Association and the Shetland Salmon
lice transfer between hosts in sea cages, and host-
Farmers Association. In collaboration with Marine-Harvest
finding may be important in the reattachment of
lice dislodged from their hosts, and for the
(1) Howse P, Stevens I, Jones O (1996) Insect Pheromones
redistribution of males searching for unmated
and Their Use in Pest Management. Chapman and Hall,London 256pp.
females6. It may also prove possible to encourage
(2) Torr SJ, Mangwiro TC (1996) Upwind flight of tsetse
lice to leave their host given sufficiently strong
(Glossina spp) in response to natural and synthetic host odour
in the field. Physiological Entomology 21 (2) 143-150.
In this initial phase, the project centres on the
(3) Fasten N (1913) The behaviour of a parasitic copepod
design and use of simple flow chambers allowing
Lernaepoda edwardsii Olsson. J Anim Behav 3 36-60.
different stimuli, present in host–conditioned
(4) Boxshall GA (1976) The host specificity of
seawater, to be proffered to lice. The copepods are
Lepeophtheirus pectoralis (Muller1776)(Copepoda:Caligidae). J Nat. Hist 8 681-700.
(5) Hull MQ (1997) The Role of Semiochemicals in the
behavioural responses. Using a digital tracking
Behaviour and Biology of Lepeophtheirus salmonis (Kroyer
system, the relative strength of these responses can
1837): Potential for Control? PhD Thesis. University of
be assessed by measuring the speed and direction
of movement. Other assays, which allow the lice
(6) Hull MQ, AJ Mordue, AW Pike, G Rae (1998) Patterns of
to exhibit preference for one stimulus over
pair formation and mating in an ectoparasitic caligid copepodLepeophtheirus salmonis (Kroyer 1837); implications for its
another, are used to gauge whether a stimulus is an
sensory and mating biology. Phil.Trans.R.Soc.Lond.B. 353
attractant. By making a choice of odours available
to the lice, we can discern which are the moreeffective.
Aqua TT – European Aquaculture Network
Aqua TT is a European Network of co-operative Universities and Industries involved in the aquaculturesector with the following main aim:
"To support the strategic goals of the aquaculture industry by facilitating collaborative university/industry action in education, training, technology transfer, research and development."
Aqua TT was founded in 1992 under the EU COMETT programme as the University Enterprise TrainingPartnership (UETP) for the European aquaculture industry. The initial proposal arose from theidentification of a clear need to systematize, coordinate and develop the training requirements of theindustry through a single body.
AQUAFLOW- European Network for the
dissemination of Aquaculture RTD information
participation in a number of EUprogrammes such as COMETT,LINGUA, FORCE, TEMPUS, FAIR,
The European Aquaculture Society (EAS), Aqua TT
and the Federation of European Aquaculture
Producers (FEAP) are jointly promoting a new EU
• Transnational exchanges of staff from
Known as AQUAFLOW, the project aims to establish
a wider and more rapid circulation of information
concerning the results and progress of EU funded(and, eventually, relevant non-EU funded)
programmes for research, technological development
and demonstration (RTD) in aquaculture. The target is
the potential end user in Europe and will include
farmers, technicians, vets and other professionalpeople who are active within the aquaculture sector.
The project works in a simple manner- each month a
number of single-page sheets will be prepared. Thesetechnical sheets will provide a concise summary of the
research project, together with the main findings and
conclusions. The sheets will then be widely
distributed, reaching aquaculture interests across
Europe. In addition a series of workshops are planned
over the 3 year period, the first being scheduled for"Aquaculture Europe" to be held in Bordeaux, France
network of almost 600 membersthroughout the European aquaculture
Aquaflow will also collect feedback from the small
and medium aquaculture enterprises (SMEs) to be able
to identify further the needs for aquaculture research
institutes, governmental laboratories and
& technology and associate information services as
well as being able to respond to problems and
bottlenecks encountered in the project.
for the European aquaculture sector.
Further information on the project available from:
Frederic Luizi, EAS Secretariat, Slijkensesteenweg 4,
8400 Oostende, Belgium Tel: +32 59 32 38 59 Fax:
Report on the 1998 sealice conference in Amsterdam
About 70 persons attended the sealice sessions at the Fourth International Crustacean Congress, July 20-24,Amsterdam. Delegates were from industry (43%) universities (41%), government (14%) and non-governmental(2%) organisations. Many of these papers have been submitted for publication and are currently undergoing peerreview. The proceedings will be published in the journal Contributions to Zoology (formerly Bijdragen tot deDierkunde). The following papers were presented at the sealice workshop sessions. Note that the titles andauthorships of papers submitted for publication in the proceedings do not necessarily match those presented at theconference.
Banks, B.A., A.P. Shinn, J.E. Bron & C. Sommerville. The
having implications for inter-host transfer of
use of RAPDs to establish the interspecific relationships of
the ectoparasitic caligid, Lepeophtheirus salmonis
Ibrahim, A., B.M. MacKinnon & M.D.B. Burt. The
influence of sub-lethal levels of zinc on smoltifying
Bashirullah, A.K. Non-interactive coexistence of two
Atlantic salmon Salmo salar L. and on their subsequent
parasitic copepods of Caranx hippos
in eastern Venezuela.
susceptibility to infection with Lepeophtheirus salmonis
Bell, S., J.E. Bron, & C. Sommerville. The distribution of
exocrine glands in Lepeophtheirus salmonis
Jackson, D., S. Deady, D. Hassett & Y. Leahy. Population
and Caligus elongatus
dynamics of sea lice on wild sea trout post smoults.
Boxaspen, K. & T. Næss. Development of eggs and
Jackson, D., S. Deady, D. Hassett & Y. Leahy. Caligus
planktonic early life stages of salmon lice (Lepeophtheirus
Nordmann as parasites of farmed salmon in
) at low temperatures.
Braidwood, J.C. The use of Crangon Crangon
Jackson, D., D. Hassett, S. Deady & Y. Leahy.
the potential environmental impact of Excis sea lice
(Krøyer) (Copepoda: Caligidae)
Bron, J.E., A.P. Shinn & C. Sommerville. Ultrastructure of
McAndrew, K., R. Wootten & C. Sommerville. Survival and
the cuticle of the chalimus larva of the salmon louse
egg production of Lepeophtheirus salmonis
(Krøyer, 1837) (Copepoda:
infections of Atlantic salmon (Salmo salar
Nordhagen, J.R., P.A. Heuch & T.A. Schram. Size as
Bron, J.E., A.P. Shinn & C. Sommerville. A description of
indicator of origin of salmon lice Lepeophtheirus salmonis
moulting in the chalimus larva of the salmon louse
(Krøyer, 1837) (Copepoda:
Roth, M. The availability and use of chemotherapeutic sea
Bron, J.E., G. Wainwright, R.P. Smullen & C. Sommerville.
Schram, T.A. The egg string attachment mechanism in
The cuticle and ecdysis in larval stages of Lepeophtheirus
(Krøyer, 1837) (Copepoda: Caligidae).
Costello, M.J. & A.W. Pike. Towards a quantification of
Shinn, A.P., B.A. Banks, N. Tange, J.E. Bron, C.
salmon lice population dynamics and infestation potential.
Sommerville, T. Aoki & R. Wootten. Comparison of 18S
Dawson, L.J., A.W. Pike, D.F. Houlihan & A.H. McVicar.
and 1TS sequences obtained from Lepeophtheirus salmonis
Effects of Sea Lice, Lepeophtheirus salmonis
, on Sea
parasitising Atlantic salmon (Salmo salar
) in Scotland.
Trout, Salmo trutta
, at different times after seawater
Shinn, A.P., Bron, J.E., Gray, D.J. & C. Sommerville.
Elemental analysis of Scottish populations of the
El-Rashidy, H. & G.A. Boxshall. Coevolution of the
ectoparasitic copepod Lepeophtheirus salmonis
parasitic copepods of the family Ergasilidae
(Poecilostomatoida) and host fishes of the family
Treasurer, J.W., A. Grant & P.J. Davies. Physical constraints
of bath treatments of Atlantic salmon (Salmo salar) infested
Firth, K.J., S.C. Johnson & N.W. Ross. Investigation on the
with sea lice (Copepoda: Caligidae).
role of skin mucus proteases of Atlantic salmon during
Tully, O., W.R. Poole, K.F. Whelan. Temporal variability in
physiological conditions of sea Trout in the marine
Grimnes, A., B. Finstad & P.J. Jacobsen. Salmon lice:
environment: Implications for the impact of Sea Lice on
Haji Hamin, H.L., J.E. Bron, A.P. Shinn & C. Sommerville.
Tully, O., P. Gargan, W.R. Poole, K.F. Whelan. Spatial and
The occurrence of blood feeding in Lepeophtheirus
temporal variation in Sea Lice infestation of Sea Trout in
Hull, M.Q., A.W. Pike, A.J. Mordue & G.H. Rae. Should I
Vikeså, V. & K. Boxaspen. The effects of salinity and
stay or should I go? New on- and off- host parasite data
temperature on early life stages of salmon lice,Lepeophtheirus salmonis
Recent publications on sealice
Collier, L. M. and Pinn, E. H. 1998. An assessment of the
and field studies of effects of dichlorvos exposure on
acute impact of the sea lice treatment ivermectin on a
acetylcholinesterase activity in the gills of the mussels,
benthic community. Journal of Experimental Marine
L. Aquatic Toxicology
Biology and Ecology, 230(1), 131-147.
McVicar, A. H. 1997. Disease and parasite implications of
Costelloe, M., Costelloe, J., Coghlan, N., O'Donohoe, G.
the coexistence of wild and cultured Atlantic salmon
and O'Connor, B. 1998. Distribution of the larval
populations. ICES Journal of Marine Science
stages of Lepeophtheirus salmonis
in three bays on the
west coast of Ireland. ICES Journal of Marine Science
Murison, D. J., Moore, D. C., McHenery, J. G., Robertson,
N. A. and Davies, I. M. 1997. Epiphytic invertebrate
Davies, I. M, Gillibrand, P. A., McHenery, J. G. and Rae,
assemblages and dichlorvos usage at salmon farms.
G. H. 1998. Environmental risk of ivermectin to
sediment-dwelling organisms. Aquaculture
, 163, 29-46.
Thain, J E, Davies I M and G H Rae, 1997. Acute toxicity
Dawson, L. H. J. 1998. The physiological effects of
of ivermectin to the lugworm, Arenicola marina
salmon lice (Lepeophtheirus salmonis
) infections on
returning post-smolt sea trout (Salmo trutta
L.) inwestern Ireland. ICES Journal of Marine Science
Grant, A. and Briggs, A. D. 1998. Toxicity of ivermectin
to estuarine and marine invertebrates. Marine PollutionBulletin
, 36, 540-541.
Grant, A. and Briggs, A. D. 1998. Use of ivermectin in
Aquaculture America ’99.
marine fish farms: some concerns. Marine Pollution
Hull, M. Q., Pike, A. W., Mordue, A. J. and Rae, G. H.
1998. Patterns of pair formation and mating in anectoparasitic caligid copepod Lepeophtheirus salmonis
(Kroyer 1837): implications for its sensory and mating
Fifth Central American Symposium on
biology. Philosophical Transactions of the Royal
Society of London
B 353, 753-764.
MacKenzie, K., Longshaw, M., Begg, G. S. and McVicar,
A. H. 1998. Sea lice (Copepoda: Caligidae) on wild
sea trout (Salmo trutta
L.) in Scotland. ICES Journalof Marine Science
World Aquaculture ’99
MacKinnon, B. M. 1998. Host factors important in sea lice
infections. ICES Journal of Marine Science
Exposition of the World Aquaculture Society.
Mo, T. A. and Heuch, P. A. 1998. Occurrence of
Sydney, Australia, 26 April - 2 May 1999.
(Copepoda: Caligidae) on sea
trout (Salmo trutta
) in the inner Oslo Fjord, south-
eastern Norway. ICES Journal of Marine Science
7th International Conference On Copepoda
O'Donoghue, G., Costelloe, M. and Costelloe J. 1998.
Development of a management strategy for the
Curitiba, Brazil, from 25 to 31 July 1999
reduction/elimination of sea lice larvae, Lepeophtheirus
, parasites of farmed salmon and trout. Marine
No. 6, 51 pp.
Rolland, J. B. and Nylund, A. 1998. Infectiousness of
organic materials originating in ISA-infected fish and
4th International Conference on SeaLice
transmission via salmon lice (Lepeophtheirus
). Bulletin of the European Association ofFish Pathologists
, 18(5), 173-180.
Schram, T. A., Knutsen, J. A., Heuch, P. A. and Mo, T. A.
1998. Seasonal occurrence of Lepeophtheirus salmonis
and Caligus elongatus
(Copepoda: Caligidae) on sea
17th International Conference of the World
trout (Salmo trutta
), off southern Norway. ICES
Association for the Advancement of
Journal of Marine Science
, Copenhagen, 5-19
Davies, I. M., McHenery, J. G. and Rae, G. H. 1997.
Environmental risk of dissolved ivermectin to marineorganisms. Aquaculture
McHenery, J. G., Linley-Adams, G. E., Moore, D. C.,
Rodger, G. K. and Davies, I. M. 1997. Experimental
Best current strategies for the control of lice on salmon farms
This document arose from the discussions at the Trondheim workshop on sea lice control on fish farms,as part of the EU Concerted Action on ”Lice control in Fish Farms”, under the FAIR programme, andwas drafted by Kjell Maroni, KPMG Management Consulting, Flatanger, Norway
The following report is made as a pointed list,
to avoid maturing females (keep the numbers
and not as an in depth advice. This is done as a
below 1 per fish, preferably zero!).
consequence of the fast development of new
• A winter treatment (November - February),
methods for lice treatment, and also is the most
region, has given very promising results (see
article by Treasurer in this issue).
• It is important to document past experience at
Prevention of infestation
a farm so as future staff can consider this inplanning further treatments.
• Use single generations sites, or if not possible,
fallow at least one month betweengenerations.
• Avoid sites found to have persistently high
biological method, using cleaner-fish (wrasse).
• Use cleaner-fish (wrasse) if possible.
The advantage is that they clean the fishcontinuously, and pick off the lice with egg
These precautionary methods will also reduce the
strings first. The disadvantage is their low
transfer of other diseases within and between
activity at low temperatures (< 6 °C), and the
method is only partly developed for big salmon (>2 kg). However, Ballan wrasse seem very
promising on such big fish (see Kvenseth article,
Caligus, Issue 2). It is necessary to avoid heavily
fouled nets, because the wrasse will feed on the
when to treat if you don’t monitor lice.
fouling rather than the lice. It is also possible to
• Motivation for lice sampling is important -
capture lice released when moving or grading
teaching about lice and “standard protocol for
Chemical treatment can be used if preventive
• Use monitoring results to get information
methods or cleaner-fish do not do the job. The
about the population structure and infection
application of chemotherapeutants by spray or dip
when grading is effective and uses and releases
less chemicals. It was agreed that in-feed
Exchange counting results between farms in
methods seem very promising, but documentation
and practical results are still scarce. For example
the time between dose and effect on lice and
• The initiatives of EwosAS and Skretting
relative impacts on chalimus, mobile and egg
(Nutreco) in distributing laminated A4 colour
Chemical methods should be chosen so that the
life cycle of the lice is broken. Bath methodseffective against juveniles should be chosen whentreating early in the life of the salmon, while
methods killing the adult lice only can be used
• The action level will depend on time of year.
Low numbers must be attained especially in
• Short term methods: Chemical treatment
the spring. The most important goal must be
• Long term methods: Cleaner-fish (wrasse)
and the consumer. However there is inadequate
co-ordination between different regulations forchemotherapeutants both within and between
countries, including the EU and EEA countries.
It is important to have cooperation between the
fish farmers and the authorities. The authorities
permitted to be released into the sea or may not
should go for a preventive strategy, and help the
have maximum residue limits established for
salmon farming industry to quantify benefits from
lice control (economic, less lice pressure on wildfish, market image).
It is felt that some countries (apart from Norway)have an over-protective strategy when it comes to
Farmers need to have the methods and best
legislation of new treatment methods. This can
advice on how to treat lice now. The priority for
result in resistance problems, and also leaves the
action here is to improve management and co-
farmers fewer methods to use under different
ordination of regulations. A longer term view
conditions. The authorities must use their “law-
identified novel areas of research which may
power” to force fish farmers who do not follow
produce more effective treatments. This includes
the agreed (co-ordinated) treatments in a region.
research into how lice find their host, if it is
Both “carrot” and “stick” are necessary!
possible to upset the digestive system of lice (e.g.
through a vaccine), and to improve techniques forthe use of different species of cleaner-fish to
control lice. Another priority is for moresophisticated and quantitative models of lice
Most chemotherapeutants used against lice have
population dynamics including their host location
been developed for other animals so considerable
behaviour and hydrographic conditions.
information already exists on their risk to staff
New delousing compound, ALPHA MAX Tmvet, from ALPHARMA successfully in use in
Pelle Kvenseth reports the following news on a new lice control compound, from talking toAlpharma, fish vets and farmers.
ALPHARMA has under general exemption from licensing, been given permission to sell a newlydeveloped delousing compound in Norway. ALPHARMA has been working with the developmentand testing of this new formula for the last four years. The new compound is a pyrethroid and is soldunder the trade name ALPHA MAX TMvet. As with all other treatment on farmed fish in Norway,both treatment and medicine must be prescribed by a veterinarian. Before permission is given by theNorwegian Medicine Control Authorities (SLK), corresponding to VMD in Great Britain, for a newdelousing compound, it has to be extensively tested. Many tests are necessary to establishconcentrations, effect on treated fish, effect on different life-stages of lice and effect on non targetorganisms and effect on the environment.
The active ingredient in ALPHA MAX is deltamethrin. The method of treatment is the traditionaluse of closed tarpaulin to surround the infected fish in a ‘bath’. Treatment concentration is 3 ppbduring 30 minutes in closed tarpaulin. The withdrawal period before slaughtering is 3 days. Thetreatment is reported to be effective against all stages of sealice, both sessile and mobile, and hasbecome very popular, especially in Western Norway and Trøndelag. According to veterinarians andfarmers, ALPHA MAX is an efficacious treatment, and it has largely replaced other bath treatmentsin several regions.
Internet e-mail discussion group for
Sealice Web site
lice biology and control
A World Wide Web site has beenestablished at
The Caligus listserver is an e-mail discussion
to host the Concerted Action Homepage.
interested in lice biology and control to provide
and request information from others in the
group. The group relies on people voluntarily
workshops and conferences, the registerof persons interested in lice biology and
control, a bibliography of sealiceliterature as well as contact details and
(a) send an email to <[email protected]
(b) leave the ‘subject’ line blank, and
(c) type in the following command in the main
CALIGUS first-name surname”. Do not include
To leave the list, send the message “SIGNOFFCALIGUS” to <[email protected]
> will send the
message to all subscribers to the group. If you
research projects, viewpoints, letters and
whether it is more appropriate to send it back to
newsletter. Please send details to Ms J.
everybody, or only to the individual who sent
the message. The latter may avoid annoying
This newsletter is funded under the European Union FAIR (aquaculture) research programme
as part of a project
entitled ‘Biology and management in the control of lice on fish farms’ (contract number CT96-1615). The project is a
‘Concerted Action’ and so does not involve new research but rather facilitates the communication of information related to
the control of lice on fish farms. This is being achieved through providing a World Wide Web site and e-mail network,
hosting of meetings (workshops and conferences), establishment of a list of researchers, farmers and authorities interested
in lice control, producing a computerised bibliography, and publishing the bibliography, newsletter, and proceedings of
The project is co-ordinated by Dr Mark J. Costello (EcoServe, Dublin) in partnership with Dr Geoffrey A. Boxshall
(Natural History Museum, London), Mr Kjell Maroni (KPMG, Lauvnes), Mr Per Gunnar Kvenseth (Norsk Hydro a/s), and
Dr Carmel Mothersill (Dublin Institute of Technology). Enquires about the project should be sent to:[email protected]
; Dr M. J. Costello, Ecological Consultancy Services Ltd, 17 Rathfarnham Rd, Terenure, Dublin
6W, Ireland; or any of the project’s partners.
Copyright statement. The information in Caligus
may be published elsewhere without prior permission for non-profiting making purposes provided its source is clearly acknowledged. Recommended acknowledgement is“From Caligus
, a newsletter funded under the EU FAIR programme”. EcoServe, December 1998
This newsletter is printed on recycled paper
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