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0/0This report not to be cited without reference to the Council*

International Council forthe Exploration of the Sea

REPORT 01' THE

C.M. 1990/F:13Session T

WORKING GROUP ON PATHOLOGY AHn DISEASES

01' MARINE ORGANISMS

(Vigo, 23-27 April, 1990)

This document is areport of a Working Group of the InternationalCouncil for the Exploration of the Sea and does not necessarilyrepresent the views of the Council

* General SecretaryICESPalaegade 2-4DK-1261 Copenhagen KDENMARK

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SUMMARY

The Working Group met for 5 days (23-27 April, 1990, at theInstituto de Investigaciones Marinas (CSIC), Vigo, Spain, with 23participants from 14 countries. National reports on diseases inmarine fish and shellfish stocks were presented from 8 countriesand discussion cent red on prevalence data in connection withconsidering possible biological effects of pollution on marinefish populations. Developments and experiences with techniquesto measure immunocompetence as biomarkers of pollution effectswere appraised for ACMP. Regarding diseases in mariculture(fish and/or shellfish), national reports were received from14 countries on the current status and these were considered withernphasis on emerging diseases and methods for their diagnosis,prevention and contro!. The WG also reviewed problems ofmedication in mariculture and agreed that a publication on thisirnportant sUbject should be produced. Considering other futurepublications, the WG agreed further additions to the ICES diseaseidentification leaflets and also that the training guide formarine fish diseases should be proposed for ICES publication.Finally, the WG proposed 3 main recommendations to be put to ICESCouncil.

RESUME

Le groupe de travail s'est r~uni pendant 5 jours (23-27 avril1990) a l'Instituto de Investigaciones Marinas (CSIC), Vigo,Espagne avec 23 participants de 14 pays. Huit rapports nationauxsur les maladies des poissons marins, crustac~s et mollusquesetaient present~s et les discussions se sont concentr~es sur desdonn~es de la pr~dominance par rapport aux effets biologiquespossible sur les populations des poissons marins provoqu~s par lapollution. Des d~veloppements et exp~riences avec les techniquespour mesurer l'immunosuffisance comrne bioindicateur des effets dela pollution ont ~t~ evaluees pour presentation au Comite d'Avissur la Pollution Marine. En ce"qui concerne les maladies dans lamariculture (poissons ou/et crustac~s et mollusques) 14 pays ontsournis des rapports nationaux sur l'etat actuel de ce probleme.Ces rapports ont ete consideres en soulignant les maladies quiemergent ainsi que les methodes pour le diagnostic de cesmaladies, 1a prevention et le contröle.

Le groupe de travail a egalement examine les problemes del'emploi des rnedicaments dans la mariculture et a concorde qu'unepublication sur ce sujet important devrait etre presentee.

En considerant d'autres pUblications futures, "le qroupe detravail a convenu que des fiches additionelles surl'identification des maladies et parasites des poissons,crustaces et mo11usques devraient etre publiees, et uneproposition devrait ~tre soumis au CIEM de publier le guided'instruction pour l'identification des maladies des poissonsrnarins.

"Finalement. le groupe de travail a propose au conseil du CIEM 3recommendations principales.

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TABLE OF CONTENTS

Section Page

1 OPENING OF THE MEETING 1

2 TERMS OF REFERENCE, ADOPTION OF AGENDA, SELECTION OFllAPPORTEORS

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3 REPORT ON THE 1989 lCES STATOTORY MEETING AND COUNCILRESOLUTIONS

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DISEASES IN WILD POPULATIONS OF MARINE ORGANISMS4

4.1 NATIONAL REPORTS ON DISEASE PREVALENCE IN MARINE FISHSTOCKS (1989)

4.2 ICES/IOC WORKSHOP ON BIOLOGICAL EFFECTS TECHNIQUES, 4BREMERHAVEN, 12-30 MARCH, 1990

4.3 NORTH SEA TASK FORCE 4

4.4 COMPlLATION AND ANALYSIS OF DATA ON DISEASE PREVALENCE 4RATES IN MARINE FISH STOCKS IN NORTH SEA, BALTIC SEAAND IRISH SEA

4.5 REVIEW OF EXPERIENCES WITH TECHNIQUES TO MEASURE 7IMMUNOCOMPETENCE AS A BIOMARKER OF POLLUTION EFFECTS

5. DISEASES IN MARICULTURE 8

5.1 REVIEW OF CURRENT DISEASE STATUS OF MARICULTURE IN ICES 8MEMBER COUNTRIES

5.2 EMERGING DISEASES AND METHODS FOR THEIR DIAGNOSIS, 12PREVENTION AND CONTROL

5.3 Vibrio STRAINS CAUSING DISEASE IN ICES MEMBER COUNTRIES 14AND VIBRIOSIS VACCINATION FAlLURES

5.4 PROGRESS REPORT ON INTRODUCTION OF GENETICALLY- 15MANIPULATED Crassostrea gigas INTO CHESAPEAKE BAY FORDISEASE CONTROL

5.5 REVIEW OF PROBLEMS OF MEDICATION IN MARICULTURE 16 •6. PUBLICATIONS 18

6.1 GLOSSARY OF TERMS USED IN PATHOLOGY 18

6.2 DIAGNOSTIC FICHES 18

6.3 PROPOSED TRAINING GUIDE FOR MARINE FISH DISEASE SURVEYS 19

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Section

6.4 OTHER POSSIBLE PUBLICATIONS

7. ANY OTHER BUSINESS

8. RECOMMENDATIONS

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ANNEX 1: LIST OF PARTICIPANTS 23

ANNEX 2: TERMS OF REFERENCE 26

ANNEX 3: AGENDA 27

ANNEX 4: RAPPORTEURS 28

ANNEX 5: SYNOPSES OF NATIONAL REPORTS ON DISEASE 29PlUNALENCE IN MARINE FISH STOCKS

ANNEX 6: SYNOPSES OF NATIONAL REPORTS ON DISEASE STATUS 33IN MARICULTURE

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REPORT OF THE WORKING CROUP ONPATHOLOGY AND DISEASES OF MARINE ORGANISMS

(Vigo, 23-27 April, 1990)

INTRODOCTION

The meeting Working Group on Pathology and Diseases of MarineOrganisms (WGPDMO) met at the Instituto de InvestigacionesMarinas (CSIC), Vigo. Spain, with Dr B J Hill as Chairman(C.Res.1989/2: 34). Local arrangements had been made by DrAntonio Figueras who welcomed the participants at 10.00 on 23April and gave abrief account on the research activities of theInstitute.

1. OPENING OF THE MEETING

The WG Chairman thanked Dr Figueras for his preparatory work andopened the meeting, welcoming the participants, particularly thenew members recently appointed by their national delegate toICES. The list of participants is attached as Annex 1.

2. TERMS OF REFERENCE, ADOPTION OF AGENDA, SELECTION OFRAPPORTEORS

The Chairman referred all those present to the Terms of Referencefor the meeting given to the WG by ICES Council via C. Res.1989/2.34 (as given at Annex 2), copies of which had beencirculated to all WG members at the beginning of the year. Healso drew attention to a letter he had received from the Chairmanof ACMP, Dr J Portmann, explaining the reason for the deletion ofthe item on seal disease which the WG had included in the list oftasks it recommended in last year's report that it should attendto at this meeting. This was because there is already an ICESworking group specifically charged with this task and neitherACMP nor the Consultative Committee felt it necessary for theWGPDMO to deal with it.

Instead, ACMP asked that the WG consider an additional item (task"i" in the Terms of Reference) concerning the possible use ofmeasurements of immunocompetence as biomarkers of. pollutioneffects. In addition to this specific item, the Chairman ofACMP had identified tasks a, band e as items of particularinterest to the Committee who wished to see the WG I S report onthese items at its meeting during June 4-15. It had beenrequested that the sections of the WG report dealing with thesetasks be sent to ICES Environmental Officer, Janet Pawlak, byearly May.

The proposed Agenda sent out to all members in advance wasdiscussed and after minor amendments was adopted (Annex 3).

The Chairman emphasised that the WG would be dealing with a heavyprogramme of work in the days ahead and in view of thedesirability of having an agreed report more or less ready by the

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end of the meeting, rapporteurs were requested to complete theirtasks as quickly as possible. The Chairman recognised thatbeing a rapporteur was not always particularly popular and tomake it less onerous on this occasion the workload would bespread amongst a larger number of. individuals than at previousmeetings. The Chairman also feIt that some recognition shouldbe given to the individuals acting as rapporteurs and he proposedto include a list of the members reponsible for individual itemsas an annex in the report. The list is shown at Annex 4.

3. REPORT ON TUE 1989 ICES STATOTORY MEETING AND COONCILRESOWTIONS

The Chairman gave abrief report on the 77th Statutory Meetingheld at the Hague, 5-13 October 1989, drawing attention to thoseitems arising which had relevance to the WGPDMO. In particular,he drew attention to the part of the report of the Mariculture •Committee dealing with the WGPDMO report. In discussion theMariculture Committee had agreed that paragraph 3 on page 10 ofthe report should be amended following objections from Francethat an item of information on Bonamia disease in Francepresented to the WGPDMO at its meeting Kiel was inaccurate. TheChairman regretted that this had been necessary and reminded allpresent of the need to ensure that statements about diseasefindings in their respective countries are supportable by fact.It was proposed and accepted that the WG's report should, fromhenceforth, identify the person responsible for compiling thenational report.

ICES Council had noted the views expressed by the WGPDMO in itslast report concerning the preferability for the editorship ofthe diagnostic fiches to rest with an active member of the WG,particularly one competent in both English and French. Thissuggestion had been discussed with the existing editors, Dr C JSindermann and Dr C Maurin, and it had been agreed to appoint DrGiles Olivier, Canada, as the new editor for future fichesproduced. The Chairman congratulated Dr Olivier on hisappointment.

4. DISEASES IN WILD POPULATIONS OF MARINE ORGANISMS

4.1 NATIONAL RE;<=P;-=O~R:.::Tc=S,---=O:.::N:......;D::.I:::S=.:EAS=:::E:::S::...-.:.P.:.:REVALE===N:;:CE=-=Ic.:.:N~MAR=:;:I:.:NE:=..~F~I.:::S.::HSTOCKS(T989)

Full reports were presented by eight countries: Belgium, •Denmark, FRG, Finland, Netherlands, Norway, Sweden and UK.Synopses of the reports are given at Annex 5. Some countries,in addition to the narrative report, presented numerical fielddata on fish disease prevalence rates on the new standardisedreporting sheets recommended in ICES Coop. Res. Rep. 166, 1989.Other countries were, however, still reporting on the old sheets.All WG members were requested to present their data on the new-style reporting sheets and to send them to the ICES headquartersfor compilation for future analysis.

No significant studies on diseases in marine fish stocks were

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carried out in 1989 by France, Ireland, Spain, Portugal, Canadaand Iceland. However, for the latter country, surveys areplanned in the near future. The Portuguese representative,Dr Menezes, reported a locally high (up to 30%) infection ofsardine with Kudoa, the enzymes of which make the fleshunmarketable if the fish cannot be cooled directly after capture.From Ireland it was reported by Dr McArdle that there had been acollapse of the sea-trout population along its west coast. Theremaining fish obviously suffered from starvation, which hasadded to the conflict between local aquaculture and anti-fishfarming groups.

No reports were received from the Baltic States of GDR, Polandand USSR, or from the USA.

Discussion of the National reports presented focussed on thefollowing points:

1. There are still big gaps in knowledge of diseases occurringin marine fish stocks and, particularly, the causes of somediseases, disorders, and starvation-related stock depletions.Every year new cases and conditions are reported to the WG, theexplanation for which in many cases remains unclear.

2. Special attention was drawn to a nUrnber of cod diseases ofill-defined or unknown cause, some of which appear to be lethal.These include "yellow pest" of young cod, X-cell disease andspleen liquefaction in older age groups. The cause (s) ofgranulomatosis in cod remains unresolved; some WG mernbers wereconcerned by the unusual report from Bel~ium of Ichthyophoniosisas a cause and requested verification through further studies.Several different types of ulcer diseases have been reported fromthe North Sea and the Baltic Sea. It is not unlikely that someof these diseases (including infection with the copepodLernaeocera branchialis in the O-group) are affecting cod stocksat the population level.

3. There was confirmation of findings of previous years thathigh prevalence of certain fish diseases can be limited toclearly defined areas of only a very few square kilometres.This is true particularly for X-cell lesions of dab along theScottish and the Danish coasts. The reason for this sharpdelineation is unknown, but it suggests that there are flatfishgroups which do not mix with other groups and which do not leavetheir localised area over a long period of time.

4. Very high prevalences of flounder diseases were reported insmall areas near to sluices in Dutch coastal waters as well as inthe centres of several German estuaries. In both cases, strongfluctuations in salinity were considered to be the direct(osmoregulation) or indirect (starvation) cause of increaseddisease prevalences. It was generally agreed that laboratorystudies under controlled environmental conditions are needed toelucidate the cause of these phenomena.

5. Interpretation of results from field surveys for diseaseprevalence suffer from the fact that the influence of fisheriesactivities on fish health has not, so far, been considered

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properly. lt is likely that these will include effects ofmechanical damage to discarded and escaping fish, thepreferential capture of fish disabled by disease and theinfluence of fishing effort on the age structure of the fishpopulation.6. As in former years, the lack of information for diseases inthe Baltic from the east European countries was regretted.lIowever, the WG was pleased to hear areport from J. Thulin thatthe supply of data on flsh diseases in these areas will improvewith the recent establishment of the Baltic Marine BiologistsWorking Group on Fish Diseases and Fish Parasites in the Baltic,whose Chairman (G Bylund) and four other memebers are alsocurrent members of the WGPDMO.

4.2 ICES/IOC WORKSHO",P~="O.;;Nc;--nBi7IO,:;;LOG;:=;:;;l;:;;CAL==--"E~F..;oF.;::E.;::C..;oT.::;S__TE=CHN=;;..:I:.JQ,,-,UE=.=S,-,-,BREMERHAVEN, 12-30 MARCH, 1990

A brief summary of the Workshop,was presented by 0 Bucke and 0Vethaak, who gave an account of the Pathology Group' sinvestigation and presented some preliminary results.. An earlyreport of the complete Workshop will be prepared by the WorkingGroup on Biological Effects of Contaminants and the final resultswill be presented at the lCES Statutory Meeting, 1991, withsubsequent publication. During discussion some WG memberspointed out that the German Bight transect investigated mightcontain different stocks of dab which could interfere with causalinterpretations of any observed differences in disease prevalencerates at the different stations. Attention' was drawn to thefact that this study programme was planned to collect broadly­based information, including several parameters of pollutioneffects and not only disease prevalence rates in dab. Otherparameters investigated included several chemlcal aspects ofwater and sediments, abnormalities of embryonie development ofdab, oyster larvae bio-assay and enzyme activities in dab. ltwas commented that these other parameters might be betterindicators for the estimation of pollution levels than thedisease prevalences of dab. The disease prevalence levels indab in the study area are al ready weIl recorded and differencesbetween certain areas seem to remain fairly constant. If dab isused as a target fish for demonstrating pollution effects, the WGfeIt that the liver seems the best organ for gross andmicroscopic studies.

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4.3 NORTH sn TASK FORCE (NSTF)

An outline of the origins of the NSTF and its current proposed •programme of field work was presented by D Bucke. The maininterest for the WG was the fish disease investigation includedin the biological effects monitoring programme. None of the WGmembers was acquainted with the programme, nor had been involvedin design of the fish disease study. This was considered byseveral members to be regrettable in view of the fact that theWG, on behalf of lCES, has put in considerable effort in recentyears in improving and standardising the methodology of fishdisease surveys and this expertise could have been made use of inthe NSTF programme planning. Some members expressed the view

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that the programme as it stood would be unlikely to add much tocurrent understanding of the situation and could be a waste ofresources.

4.4 COMPlLATION AND ANALYSIS OF DATA ON DISEASE PREVALENCE RATESIN MARINE VISS STOCKS IN NORTS SEA, BALTIC-S:EA~ IRISS SEA

A sub-group of 4 members of the WGPDMO ( D Bucke, S de Clers,J Thulin and D Vethaak) was formed at the meeting to evaluatethe present status of available data and the methodology ofcollecting and analyzing disease prevalences in marine fishstocks in the ICES area. They met separately and reportedback to the full WG with their findings as foliows:

Consideration was given to the quantity and quality of thedata. It almost exclusively concerned the North Sea.Information on prevalences of fish diseases in the BalticSea is still very inadequate. The conclusion was that datamore than 3 years old would prove difficult if notimpossible to analyse. The principal problems defined wereassociated with diverse study designs (notably small samplesizes and lack of length standardisation). A paperdedicated to this subject is to be submitted forpresentation at the 1990 lCES Statutory Meeting by D.Vethaak.

Using data for the North Sea as a model, the statisticalanalysis required is an interpretation of long-term trends(Le. over a minimum of 5 years) for the prevalence ofdiseases in each station, separately, and for the North Seaas a whole. The data should be presented, through maps andtables, on a background of biotic and abiotic data collectedindependently by other lCES working-groups.

A standardised methodology has been developed to reportannually on selected fish diseases (see Methodology ofFish Disease Surveys, ICES Coop. Res. Rep. 166) and,additionally, a supplementary ICES Training Guide forFish Disease Studies iss being prepared by the WGPDMO.Some WG participants now use standardized forms topresent their data and most North Sea countries have beenusing the standard methodologies for the last 3 years.The scope of the statistical data analyses agrees withthe aims and recommendations of ICES. Only datareported in the standard format, when compatible, couldbe considered by the sUb-group, but some mernber countrieshave other prevalence data which could be made compatibleover a longer period.

The data reported to ICES by the WGPDMO describes thenurnber of fish affected with a chosen nurnber of diseasesin a total number of fish examined on one station at agiven date. The information also included thefollowing: sampling year and month; mean length (+/-SO)of fish in three given length groups by sex and fishspecies. Two minor modifications of the ICES reportingform are recommended by the sub-group:

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(a) the exclusion of X-cell gill lesions for dab on thegrounds that most infected fish are smaller than therecomrnended length size for sampling, thus not beingnoted on the forms.(b) the inclusion of the condition factor for guttedfemale dab of the 20-24 cm length range.

The sub-group identified two directions for futurestudies on statistical methods:

(a) research to develop new statistical tools forassessing the significance of variables not reported todate. For example: the age of the fish in the sampie,and the occurrence of several diseases in a single fish.lt was also feIt that for some diseases (e.g.lymphocystis) the prevalence coding should besupplemented by an intensity code.

(b) routine data analysis performed by lCES usingexisting statistical techniques and data. For theanalysis, the use of Generalized Logistic Models issuggested. These models can identify the stations withstatistically different prevalences, and can provideobserved and expected va lues to be illustrated on lCESmaps.

The WG will determine for each disease the difference inprevalence judged to be biologically significant.Levels of significance depend on e.g. natural samplingvariability and spatial patchiness of the disease.

The following is a list of variables needed as backgroundinformation for the lCES subsquare nearest to thesampling coordinates:

Abiotic variables

- standard hydrographical parameters- sediment composition- contamination characteristics.

Biotic variables

These variables refer to any fish species used as a modelto monitor diseases (e.g. dab, flounder, cod):

- characteristics of the benthic comrnunity,- catch composition of other fish species.

On the model species the following parameters are alsoneeded:- catch per unit effort,- general stock assessment information available to leES,- annual age-length keys,- map of fishing intensity,- stock separation and migration pattern,- stomach content analysis.

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Conclusions:

1. The use of the revised ICES reporting forms inconjunction with the proposed ICES training guide onmarine fish diseases is to be strongly recornrnended.

2. At the beginning of each year WG mernbers shouldprovide the ICES-Secretariat with data of the previousyear to analyse. These results are to be returned tothe WG in the form of prevalence values on. maps andtables.

3. The first evaluation by the WG of trends should takeplace in 1992.

The WG accepted the sub-group I s report after discussion on thecurrent relative lack of information about disease prevalences infish stocks in the Baltic Sea. lt was welcomed that resultsshould be forthcoming in the future via the new BMB WorkingGroup. There was also discussion about the possibilities forindividual countries to re-evaluate and standardise older data tobe compatible with the recent data submitted on the new-stylereporting forms. The WG decided that the proposed manner ofhandling the submitted fish disease data forms should be made asa Recornrnendation in the WG report.

4.5 REV7EW OF EXPERIENCES WITH TECHNIQtrES TC MEASUREIHMONOCOMPETENCE AS ABIOMARKER OF POLLUTION EFFECTS

The Chairman explained that this agenda item was given to the WGby ACMP arising from remarks in the 1989 WGPDMO Report. Thequestion being asked was whether methods currently in use havebeen sufficiently developed to be applicable to field situationsand to consider whether irnrnunocompetence could be used as analternative assessment method for biological effects monitoring.A summary review paper by B A Weeks et al. entitled"lmmunocompetence to Assess Environmental Stress" had beenprepared for the WG at the request of the Chairman. During itsdiscussion the following were the main points to arise:

(1) Knowledge of the irnrnunology of the marine fish speciesinvolved in current disease studies is limited. The informationavailable indicates that pollution may affect the irnrnune systemof fish and there is some knowledge of particular elements of theimmune system responding to specific pollutants. Many otherfactors such as nutritional status, maturity and temperature canaffect irnrnunocompetence so the appearance of changes in immuneparameters in polluted areas may not necessarily indicate apollution effect. Although in fish farms the relationshipbetween environmental stress, decreased immunocompetence andincreased disease with associated mortality is weIl established,this information is generally lacking for wild marine fish.ldeally, assessment of disease levels in populations asinfluenced by pollution should precede measurement ofimmunocompetence.

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(2) An additional indicator of pollution which has an unknownbiological significance is not desirable. It is thereforenecessary to determine the relationships between the degree ofchange in the immune status of fish and the degree of change insusceptibility to disease and survival. Measured alterations ofaspects of the immune system do not necessarily indicatesignificant change in disease susceptibility, possibly only thatthe fish is responding or adapting. The use of laboratory basedtrials such as those taking place in the Netherlands, FRG,England and Scotland are to be encouraged and particularly theuse of disease challenge trials following exposure tocontaminants.

(3) Field studies have not demonstrated conclusively acause/effect relationship between pollution and alteration of theimmune status in marine fish, or even that the two areconsistently or directly correlated when changes are found.Analysis of existing data on multiple diseases in individual fishcould indicate if pollution was acting on non-specific immunemechanisms.

Conclusions:

Evidence for immunosuppressive effects of pollution have beendemonstrated in experimental systems and in the fresh/brackishwater field situations. The frequency, reliability, specificityand significance of such changes in marine fish is poorlyunderstood at present and available knowledge is not yet directlyapplicable to field studies with any degree of certainty. Forprogress towards this objective, research is required on theinfluence of different environmental factors (pollution and non­pollution) on the immune status of fish. The normal range ofvariability in immunocompetence must be determined andinformation obtained on the validity of extrapolation of datafrom individual fish and experimental systems to wild fishpopulations.

S. DISEASES IN MARICOLTURE

5.1 REVIEW 01' CURRENT DISEASE STATUS 01' MARICOLTURE IN ICESMEMBERCOUNTRIES

written reports were submitted to the wG by 13 member countries:synopses are given at Annex 6. During discussion the mainproblems identified were as folIows:

(a) FIsa

(i) ATLANTIC SALMONIPN was isolated in Canada (B.C.) for the first time with aserotype different from Ab, Sp and VR 299 strains. An increasein outbreaks of II?N was observed in Scotland giving cause forconcern because of evidence for synergistic effect with pancreasdisease in concurrent infections.

Infectlous salmon anaemla (ISA) isNorway; 64 farms are affected and,

an increasing problem inas with furunculosis, the

No new developments in the vibriosis situation were

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disease is considered as one of the most economically importantdiseases in this country.

Panereas-disease is a growing problem in many countries and iscurrently the most serious problem in Atlantic salmon culture ofIreland. The severity seems, to some extent, to be related tostock management on the farms.

Cold water vibriosis (Hitra disease) was observed in Canada forthe first time, so far only associated with low mortalities. InNorway, Hitra disease seems to be under control due to widescalevaccination.

Furunculosis, caused by Aeromonas salmonicida, continues to bethe most serious disease of marine farmed Atlantic salmon. InIreland, Scotland and Canada problems of antibiotic resistanceare occurring. In Norway, furunculosis has spread both northand southwards, and is threatening the most important Atlanticsalmon farming areas. Furunculosis has spread along the Balticcoast of Sweden and seems also to affect the wild broodstock.Furunculosis was detected for the first time in Spain. In boththe Norwegian and Baltic situations, the disease seems to spreadby escaped salmon and 'wild' fish. A new vaccine againstfurunculosis is under development in Scotland.

Vibriosisreported.

Enterie redmouth disease is no longer a problem of anysignificance in salmon farms in Norway, or in other countries.

Bacterial kidney disease was detected for the first time inFinland, probably originating from Sweden where it was observedfor the first time in 1987. It seems that this disease spreadsrapidly in the Baltic area where there is low salinity (5.6°/~).

Sea lice infestation remains a serious parasitic problemfor cageculture of Atlantic salmon. New drugs have been tested andshowed promising results (Ivermectin, Ireland; Pyrethrum,Norway). A vaccine is in the experimental stage in Scotland.

The parasites Hexamita salmonis and Gyrodactyloidesbykowskii have been reported for the first time in marine salmonculture in Norway.

Conclusions:

There is an apparent serious trend of increasing disease problemsin Atlantic salmon farming with well-established diseases such asfurunculosis, sea lice and pancreas disease, although somediseases, such as coldwater vibriosis in Norway, have beenbrought under control through use of vaccine. The increaseddisease problems have contributed in a large way to decreasedperformance and increased mortalities in salmon farmed inseawater. Developments in vaccine and chemical contral methodsare weIl in progress in several ICES countries, but also thetrend is towards greater control through management techniques(e.g. reduction in stocking densities and fallowing of sites),

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particularly in Scotland and Norway.

The WG noted that viral disease (especially IPN) anddiseases suspected to be of viral aetiology (pancreas disease andILA) are increasing at an alarming rate. This is a cause formajor concern because these diseases are not treatable and canonly be controlled by substantial changes in farm managementpractices. Since diagnosis of these diseases can beproblematic, because the viruses cannot be cultured in vitro asyet, even the use of management tools can be very difficult andnot entirely effective. A strong effort to increase virologicalresearch on farmed Atlantic salmon is urgently needed.

(ii) OTHER SALMONIDS

IPN virus of the He serotype was recorded for the first time introut in Finland: it has previously been found only in Germany.

Pancreas disease, associated with low mortalities, has beenobserved in brown trout in France. This is the first record ofthis disease in a species other than Atlantic salmon.

Furunculosis is spreading rapidly amongst rainbow trout farmsalong the Baltic coast of Finland following the first cases in1988.

Conc1usions:

As culture of "other salmenid species" has not expanded at thesame speed as Atlantic salmen culture, outbreaks of new diseasesor changes in present disease status have been much less.

(iii)OTHER FISH SPEeIES

IPN virus has been iselated from both turbot and halibut inNerway, but whether this is a cause ef observed mortalities isnot clear. However, in France, astrain of this virus has beenshown te be pathogenic fer juvenile turbot.

Vibrio angui~~arum is the main causative agent in epizootics injuvenile turbot in Spain. A new Vibrio sp. related to V.anguillarum, V. splendidus and V. pelagius, has been involved indisease problems in most cultured species in (Galicia) Spain.In turbet, where this bacterium has caused disease, there was anassociated iridovirus infection ef, as yet, unknown significance.

Costiasis was, fer the first time, the apparent cause ef a •significant mortality in sea bass in France.

Conclusions:

The increasing culture of new fish species, e. g.. turbot andhalibut, is promoting new disease problems, including untreatableviral infections. The WG again identified the pressing need forincreased efforts in virological research in mariculture.

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(b) SHELLFISR

(i) MOLLUSCS

(1) Rudltapes philippinarum

"Brown rinq disease" (Vibrio sp. P1 tentative1y identified as thepathological agent) of Ruditapes phllippinarum has beencontrolled successfully in France by destruction of infectedstocks. A regular epidemiological monitoring survey for thedisease is now in progress. Moreover, an efficient preventivetreatment of spat has been establ1shed. Brown deposits inshells have been detected in several individual R. philippinarumin Spain, but these were not clearly associated with anypathology and a few individual clams have been found infectedwith Perkinsus sp.

(2) Rudltapes decussatus

A drop from 80% to 20% in mortality caused by Perkinsusatlanticus was reported for c1ams cultured in Portugal. Thisimprovement was achieved by the introduction of better managementtechniques.

(3) Ostrea edulis

Bonamia ostreae has shown only limited spread to new sites inEngland, Ireland and the Netherlands. The ELISA detectiontechnique"has been used effectively by some member countries fordetecting low prevalences of the disease organism in lightly­affected stocks, but histological examination was still beingwidely used for monitoring purposes.

Marteilia rerringens has shown a resurgence of virulence andspread in o. edulis in France. In Spain, where intensiveepidemiological studies of this species are being carried out, nosimilar resurgences have been reported. Ostrea puelchana hasbeen found to be sensitive to M. refringens by French scientists.

(4) ~ilus edulislgalloprovincialis

Marteilia spp. There is a continuing problem for regulation!control for the two Marteilia spp. (M. maurini and M. refringens)due to the difficulties of distinguishing between both the musselspecies and the parasite species.

~ilicola intestinalis. Although no mortalities or pathologyhave been directly associated with infection by this copepod, thehigh prevalences in some areas and the possibility ofdebilitatory effects in conjunction with other pathogens orenvironmental stresses led some WG members to suggestcontinuation of present precautions against further transfer ofthis pest to high density!value musse1 cultivation areas ••

(5) Crassostrea virginicalgigasRecent increases of infections with the protista, Haplosporidiurnnelsoni (MSX) and Perkinsus marinus throughout Chesapeake Bayhave almost decimated the remaining C. virginica population.

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Susceptibility trials with C. gigas are ongoing.

(6) Argopecten irradians

A new Perkinsus-like protozoan has been identified in bayscallops from Canada. Pathogenie proliferation appearsrestricted to the pre- and post-spawning period when the bayscallop is moribund. ldentification, transmission andpathogenieity studies are ongoing. Concern was raised that thisparasite may have been originally introduced to Canada from theeastern coast of the USA despite rigourous quarantineinvestigations following lCES guidelines on the introduction ofnon-indigenous species.

(7) Pecten maximus

Epidemiologieal studies suggest that the Rickettsia sp.discovered in the gills of scallops suffering from mortalities inFrance may be the cause of the pathology.

(8) Mercenaria mercenaria

On investigation of a 50\ mortality of hatchery-reared quahogs(1-2 years old) in Canada, the animals were found to be infectedby a previously undeseribed protozoan (possibly a gregarinespeeies).

Conclusions:

Bearing in mind the endemie nature of diseases in most eountrieswith molluscan aquaculture, it is important that the quality ofmanagement of cultivated stocks be assured. There is acontinued need for improving epidemiological surveys. Speed ofanalyses will soon be enhanced by the development of diagnostietechniques which can be automated , e.g. immunodiagnostics andDNA probes. Moreover, it was recognised that the development ofcell line cultures for investigation of molluse diseases ofpossible viral aetilogy is of utmost importance and the currentresearch in this field is to be encouraged.

(H) CRUSTACEA

Fusarium solani was reported in brood stocks of cultured prawns(Penaeus japonicus) in Portugal where there is a rapid expansionof production taking place.

5.2 EMERGING DISEASES AND METHODS FOa THEIR DIAGNOSIS,PREVENTION AND CONTROL

The WG consldered reports of a number of emerging diseaseproblems affecting cultured fish and molluscs in leES membercountries and the attempts belng made to control them. The mostsignificant of these are as fallows:

13

(i) Infectious anaemia in Atlantic salmon (ISA)

This disease is now regarded oneimportant emerging disease in Norway.

of the most economicallyThe major features are:

(a) mortalities on affected farms can reach more than 70%in some instances,

(b) fish of all sizes can be affected, mostly after smoltshave been introduced in sea water,

(c) affected fish (apparently only Atlantic salmon) showsluggish behaviour and a variety of clinical signs: lowhaematocrit values, pale gills, ascites and haemorrhages(particularly in liver),

(d) transmission experiments haveinfectious, and possibly to have a viralcultures have not been achieved, virus-likeseen in blood cells.

shown it to beaetiology, althoughparticles have been

(e) control is limited to stock reduction, but because theblood from affected salmon can be considered as infectious, it isimportant that attention be paid to slaughter houses as a sourceof transfer to new areas.

(ii) Pancreas disease in Atlantic salmon

From Scotland, there was information demonstrating that:

(a) the disease is highly infectious and on the increase,

(b) mortality can be significant, particularly with thesecondary involvement of other pathogenic factors,

(d) there is no control, apart from the limitation ofstressing factors.

(iii) Protozoal (micrcsporidian) disease in turbot

In France and in Spain, microsporidia were found encysted inviscera and muscle of turbot. Although the impact on health ofaftected fish seems not to be significant, possible effects onmuscle tissues could make the fish unsaleable. Control measuresare not available and the essential supply of juveniles from thesmall number of hatcheries makes health regulations difficult toapply without severe impact on this developing industry.

(iv) A form cf Vibricsis in clams

A Vibrio sp (strain PI) is believed to be responsible for theformation of a "brown ring syndrome" in the clam Ruditapesphilippinarum. However, the disease can be controlled by thetreatment of spat in a bath of Furazolidone (10 ppm, 3x24 h).

14

(v) Rickettsiae in sca110p (Pecten maximus)

In Franee, mortalities in natural beds of seallops may beassoeiated with a riekettsial gill infeetion. This type ofdisease in wild populations eould easily be overlooked andsensitive methods should be employed for diagnoses. Nueleotideprobes eurrently being developed eould be useful for anepidemiologie survey. The initial rearing of young seallops innon-infected areas eould limit the subsequent development ofinfeetion when they are later introdueed onto infeeted beds.

During a slide workshop, specimen mieroseope slides of a varietyof disease eonditions were examined and usefully diseussed,particularly those eoneerning:

- Infectious anaemia in salmon (ISA)- Turbot mierosporidiosis- Salmon liver granulomatosis- Turbot liver degeneration- Recently discovered pathogenie protozoan in Juvenile quahog- A Perkinsus-like protozoan in bay scallops from Canada.- Halibut gill-aporocyte (blood fluke) eggs.

From the discussien, the WG agreed it should draw the attentionof the Mariculture Cemmittee to the following peints:

(al There is a serieus disease risk in imperting salmon smelts,or other juvenile fish, er mellusean spat fer culture in ethereountries. If such an importatien is necessary, healthcertification sheuld be obtained frem cempetent authorities.

(b) Beeause of the serious ecenemie threat ef infectieus anaemiaef salmen (ISA), enly eviseerated salmen should be imperted forccnsumption from affected eountries.

(cl There was concern from the WG that new virulent virus ervirus-like diseases are emerging in mariculture, hut yet there isa laek of expertise available te research these problems becauseof a general reductien in this area of research in ICEScountries.

(d) More sensitive methods for detectien ef pathegens eausingserieus diseases in fish and shellfish need to be develeped.

5.3 Vibrio STRAINS CAUSING DISEASE IN ICES MEMBER COUNTRIESAm> VIBRIOSIS VACCINATION FAILURES

At the 1989 meeting cf the WGPDMO seme members suggested thatthere was need to conduct a small-scale collaborative study onseme ef the difficulties with identification of Vibrio spp. Onespecific question identified was: "When we are referring to•vibriosis I in fish, are we all referring to the same thing?"In order to answer this a sub-greup ef 5 WG members was fermed tocarry eut an inter-sessienal task of exchanging strains of vibriospp. from their eulture eolleetions and identifying them

methods, with optionalserology and the use of

15

according to their own laboratoryadditional tests like pathogenicity,rapid identification systems.

During the WGPDMO meeting in Vigo the sub-group met separately todiscuss their results. The amount of data generated on thecharacterization of these isolates was too great to allow a fullanalysis in the time available, but some interesting conclusionsabout vibrio strains and vibriosis were reached:

(a) almost identical strains occur in many European countriesand in Canada.

(b) there is a need for standardization of all techniques,biochemical and serologieal, to allow comprehensive comparison ofresults.

(c) there is a need to develop an identification key forbacterial pathogens of fish and to evaluate the possibility ofusing a modified rapid identification system for this purpose.

(d) further essential experiments on the pathogenicity of manyof the "vibrio"isolates need to be carried out.

(eI although the study by the sub-group was not completed, allmembers were very satisfied with this collaborative effort andhave agreed to pursue additional comparative studies before thenext WGPDMO meeting.

(f) apart from a few odd exceptions due mostly to mis-use,vibriosis vaccination now seems to be performing well in all ICESmember countries.

5.4 PROGRESS REPORT ON INTRODUCTION 01' GENETICALLY-MANIPULATEDCrassostrea gigas INTC CHESAPEAKE BAY rCR DISEASE CONTROL

Areport from E Burreson, USA, was received with informationabout the proposal of introduction of Crassostrea glgas into theChesapeake Bay to rejuvenate the oyster industry that has been~ecimated by diseases of C. vlrglnica.

Diploid and triploid Crassostrea glgas have been held inquarantine systems at the Virginia Institute of Marine Scienceand exposed to Perklnsus marlnus for periods of 3-5 months.Diploid and triploid strains of native eastern oysters,Crassostrea vlrglnlca, served as susceptible controls. In anexperiment using flowing seawater with treated effluent,Crassostrea gigas did become infected with Perklnsus marinus, butthe prepatent period was much longer than in C. virginlca andintensity of infection remained low in C. gigas compared withinfections in C. vlrginica. Most C. virginlca had already diedby the time infections first appeared in C. glgas. Inrecirculating systems, most P. marinus infections remained lightin all treatment groups, including C. virginica, makinginterpretation difficult. Data suggest that C. glgas can becomeinfected with P. marlnus, but the parasite is not pathogenic.There appears to be no difference in the susceptibility of

16

diploid and triploid strains. Laboratory challenge withHaplosporidium nelsoni (MSX) has not been possible because theinfective stage is unknown. Arequest has been made to theappropriate Virginia management agency for field challenge on asmall lot of C. gigas to begin 1 May 1990 in the lower ChesapeakeBay. This small-scale introduction will provide data by1 October 1990 on susceptibility of C. gigas to both P. marinusand H. nelsoni under natural conditions.

The WGPDMO expressed great interest in the report but,unfortunately, no representative from the USA was present toreply to the many quest ions that the information generated.Because of the applicability of these studies to other membercountries, such as Canada, France and Spain, the WG stronglyencouraged continuation of these studies. Specific membersinterested in the progress and details of this research will becontacting the USA representatives directly and it is hoped thatmore information will be provided by a US representative at thenext WG meeting.

5.5 REVIEW OF PROBLEMS OF MEDICATION IN MARICULTORE

The WG received the following papers (by the identified authors)which had been prepared as an inter-sessional task as agreed atthe 1989 WGPDMO meeting:

Diseases currently lacking medical treatment (variousmembers)

Justification for medication in mariculture (F Baudin­Laurencin)

Pharmacokinetics and drug residues (D Alderman)Public health implications of medication in mariculture (G

Bylund)Development of drug resistence (J McArdle and B Hjeltnes)Interactions between antibiotics and immunity in fish (G

Olivier).

Following the presentations, the various topics were discussed bythe WG and the following conclusions reached:

1. Medication continues to be a useful and necessary means ofcontrolling certain infectious diseases in farmed fish. Becauseof the nature of marine fish farming, disease will inevitablyoccur and medication is one of the most important ways ofcounteracting the economic losses due to such disease. Viraldiseases present a particular problem because of non-existence ofvaccines and medication to prevent and treat such diseases.

2. All participants reported increasing problems of drugresistance, ineluding multiple resistanee, which taken togetherwith the relatively few licensed antibiotics available for use inmarine fish farming will have a significant impact on the abilityto control infectious disease problems in the ICES area in thevery near future.

3. The main publie health implications arising from the use ofantibiotics and other types of medication in the marine

•

17

environment recognised by the WG were the accumulation ofresidues of pharmacologically active compounds in the flesh oftreated fish and the potential for transfer of resistence tohuman pathogens present in the marine environment in the area offish farms. Whilst the WG did not seek to minimise such risksthe scientific evidence currently available does not currentlyindicate that these phenomena pose areal public health risk atthis time.

4. To ensure the continued efficacy of medicines used in marineaquaculture and to minimise the public health risks from the useof such medicines, adequate controls on the availability of somemedicines is necessary.

5. The wG feIt that aprerequisite for the effectiveness ofmedication in marine fish farming was accurate and earlydiagnosis based on clinical history and disease signs and, wherepossible, supported by laboratory tests particularly isolation ofcausative pathogens and antibiograms.

6. The WG reviewed the role of medication and its effect onimmunocompetence in fish, and concluded that the availablescientific information was sparse and, in some cases,contradictory making a definitive conclusion impossible.However the small amount of information available calls for arational and restrained use of antibiotics and the avoidance oftheir prolonged use.

Based on the foregoing conclusions the WG agreed the followingneeds:

(i) Improvement of disease treatment strategies

It is feIt that there is a good deal of scope for research anddevelopment in improving the methods in which medicines can bepresented to the fish. Reports on novel sea lice treatments anddrug encapsulation are encouraging, although at an early stage ofdevelopment.

(ii) Encourage vaccination programmes

The effectiveness of a nUmber of fish vaccines against suchdiseases as vibriosis and Hitra disease is now generallyaccepted. The preliminary reports on the development ofvaccines against sea lice and genetically engineered vaccinesagainst furunculosis are also encouraging. The WG feIt that theuse of vaccines, where possible, should be encouraged in the leESarea as a preferred method of controlling disease to the use ofchemotherapy and help reduce the amounts of antibiotics and othermedicines being used.

(iii) Improve management at fish farm level

The WG recognised the need to optimise environmentalconditions, reduce stress and maintain good husbandry practices(e.g. fallow periodsl in marine fish farms for reducing theoccurrence of disease outbreaks and hence quantities of medicinesused.

18

(iv) Education for aguaculturists

The WG recommends that aquaculturists should receive adequateeducation in the correct use of antibiotics and therapy.

(v) Legislation

The WG recommends that governments in the leES area ensure thatadequate regulations are in place and enforced to control theavailability of medicines and chemicals used in marineaquaculture.

Finally. the WG agreed that the review had been a useful exerciseand that, with some expansion, the different papers preparedshould be amalagamated into a single review paper for publicationby lCES. lt was agreed that a draft should be prepared in timefor distribution to all WG members for consideration be forediscussion and approval at the next meeting. A lead authorwould be needed to co-ordinate the contributions and the WGunanimously accepted the proposal that this should be Dr 0Alderman.

6. POBLlCATIONS

6.1 GLOSSARY OF TERMS USED IN PATHOLOGY

Dr F Baudin-Laurencin and 0 Bucke presented a copy of theirGlossary of pathological Terms. The WG members commended theauthors for their work. lt was recognized that there are stillsome amendments to be made. WG members were asked to send theircomments to 0 Bucke before May 31, 1990. The final copy of theGlossary will then be sent to Dr H Rosenthai, Chairman of thelCES/ElFAC study group. However, the WG members recommend thatthe glossary of pathological terms should be published as aseparate entity by lCES. instead of simply being incorporatedinto the lCES/ElFAC Glossary on Aquaculture Terminology. Theadvantages of having aseparate document were feIt to be:incorporation of French terminology; expansion of somedefinitions; and addition of more terms, particularly those ofgreater relevance to fish disease surveys than to aquaculture.

6.2 DIAGNOSTIC FICHES

The latest series of leaflets (Nos 41-50) are currently beingedited. All WG members were concerned by the lack of publicitygiven by lCES to the availability of these fiches. It wasrecornrnended that scientific associations such as the EuropeanAssociation of Fish Pathologists and the American FisheriesSociety should be advised via their bulletins/newsletters aboutthe existence of these leES publications. It was also agreedthat the drafts of the next block of fiches (Nos.51-GO) should beconsidered at the next WG meeting.

e·

•

19

6.3 PROPOSED TRAINING GOlDE FOR MARINE FISH DISEASE SORVEYS

As decided at the 1989 WGPDMO, 0 Bucke, T Lang and 0 Vethaakprepared (as an inter-sessional task) a draft Training Guide withillustrated examples (colour prints) of the more common diseasesof marine fish with brief descriptions. The Training Guide isintended to be used for disease identification on field surveys.The WG members were very satisfied with the Training Guide andrecommend its rapid pUblication by ICES after minor amendments.The Guide will be very valuable as a complement to the lCESCooperative Research Report No.166, on the "Methodology of FishDisease Surveys", and will help to standardize such surveysbetween different countries. The WG, as a whole, recognized theneed for early publication of this document, possibly within thenext year and agreed that the final version should be submittedas soon as possible to leES. As this Guide is intended for useat sea, it will need to be printed on plasticized sheets, in aring folder, with colour illustrations (similar to the ICES"Plankton Identification Fiches").

6.4 OTHER POSSIBLE POBLICATIONS

It was suggested that the WGPDMO should prepare a video for ICESproduction as a complement to the Training Guide to help in thetraining of non-specialists prior to and during participation infish disease surveys. Members of the WG will consider how thismay best be approached and will discuss proposals at the nextmeeting.

As agreed under item 5.5, it is recommended that a multi-authorreview paper on the problems of chemotherapy in mariculture beprepared with Dr D J Alderman as the leading author.

7. ANY OTHER BOSINESS

(a) Future activities

(i) Liaison between WGPDMO and OIE.

It was pointed out to the WG that the Office International desEpizooties (OIE) has a Fish Diseases Commission with the remitbeing to consider serious diseases of aquatic anima1s and to makerecommendations to national authorities through its Animal HealthCode on appropriate health certification procedures and controlsto prevent disease spread through internationaltrade in livefish and shellfish. lt was suggested by some WG members thatperhaps it would be useful to have some liaison between WGPDMOand OIE, particularly concerning information on disease problemsin mariculture and advice on international effort to preventspread. There was not a clear view on how this could beachieved and the Chairman pointed out that ICES WGs should notcommunicate directly with outside organisations or issue any oftheir reports without prior clearance by Council. The matterwas left unresolved.

20

(ii) The influence of nutritional problems on the health ofmarine organisms.

The WG considered whether this should be an area for discussionin future meetings. It was concluded that, in view of the factthat other groups in ICES and EIFAC are involved in this area,and that the main purpose of the WGPDMO members is primarily withpathological conditions, it was agreed that only cases ofdiseases caused by nutirion should be considered by the WG andthat data on these could be included in the national diseasereports.

(b) Direotory of specialists

A proposal that a detailed list of specialists working onresearch topics (mode lIed on the Frisk Fisk Norwegian Programme)be published was rejected because of the problems of the constantneed for updating. It was agreed, however, that it would beuseful if each national report to the WGPDMO oould have anaddendum listing current research projects on diseases of marineorganisms in that country to be included as an annex of the WGreport.

(0) National Reports

In future, the following protocol will be followed to avoidlengthy discussion du ring the WG meeting:

(i) Full national reports will be sent to all members of the WGweIl in advance of the WG meeting.

(ii) A synopsis of each national report for direct inclusion inthe WG report will be provided by each country's representativeto the Chairman prior to WG meeting.

(iii) Only significant changes or trends during the previousyear should be identified by each country's delegate and a shortdiscussion prepared for presentation at the WG meeting.

During the WG meeting specialist interest sub-groups (e.g salmondiseases, mollusc diseases) should meet, separately, to discussthe details or trends and developments within their specialistarea, and subsequently make areport with recommendations to thefull WG.

(d) Baltlc Marine Bioloqists (BMB) Working Group 25 (HG 25)

BMB is a group of independent biologists from the Balticcountries, and WG 25 was formed to consider fish diseases andfish parasites in the Baltic. Drs Thulin and Bylund reportedthat accounts of WG 25 metings, symposia and field studies(cruises) will be made available to ICES through meetings of

WGPDMO.

WGPDMO commended the initiative being shown by this organisation

•

21

and welcomed the prospect of improved provision of much-neededdata on marine fish disease from all Baltic countries.

(e) ICES/EIFAC Codes of Practice and Manual of Procedures forConsideration of Introductions and Transfers of Marine andFreshwater Organisms

In light of recent advances in diagnostic techniques, changingdisease profiles and appearance of new diseases in molluscs, itwas pointed out that some of the disease aspects of the "Codes ofPractice" guidelines, particularly Appendix 1, are in need ofupdating. It was agreed that relevant members of the WGPDMOshould review the current molluscan disease control guidelinesfor each country as an inter- sessional task and report on thesefor discussion at the next WG meeting.

(f) Impact of disease on marine fish stocks

It was feIt by several WG mernbers that lethaI or acute diseasesin marine fish stocks are likely to have more serious effect atpopulation level than chronic on-going diseases used ininvestigating pollution effects. A review of current andhistorical data on lethaI diseases of wild fish is necessary inorder to see which should be taken into account, for improvingunderstanding of population dynamics as part of stock assessment.WG mernbers will give further thought to this during the inter­sessional period and discuss again at the next meeting.

8. RECOMMENDATIONS

(1) As a consequence of ICES resolution (C. Res. 1989/2.34),data on diseases in marine fish stocks is being collected bymernber countries and compiled on an annual basis for submissionto ICES. It is recommended that ICES statistically process thisdata according to the guidelines presented in WGPDMO 1990 (Reportsection 4.4) and the results returned to the WG forconsideration.

(2) It is recommended that current mo11uscan disease controlmeasures for each ICES country and their applicability to new oremerging diseases, changing disease profiles as well asdiagnostic techniques be evaluated in order to update the diseaseaspects of the ICES/EIFAC Codes of Practice for introductions andtransfers of marine organisms.

(3) That the WGPDMO meet for 4 days at the Fisheries ResearchSta.tion, Ostende, Belgium, 19-22 February 1991: under the Chairmän­Sh1p of Or B. Hill~ to carrY'out the following tasks:

(al to consider the National Reports on diseases in wildand shellfish stocks throughout leES mernber countries,special reference to the anticipated new information beingavailable from Baltic countries;

fishwithmade

22

(b) to consider recent disease trends and developments inmariculture throughout ICES member countries, with specialattention to advice on preventive and control measures;

(c) to receive a review of current molluscan disease controlmeasures in ICES member countries in order to provide advice onupdating the relevant ICES!EIFAC "Codes of Practice" guidelineson introductions and transfers of non-indigenous organisms;

(d) to review current and historical data on lethal diseases ofwild marine fish and consider the possible relevance to stockassessment;

(e) to review information on dab (Limanda limanda) and flounder(Platychthys flesus) migration habits, as these may haverelevance to studies on disease prevalence in polluted areas ofthe North Sea, Baltic Sea and Irish Sea.

CLOSING CF THE MEETING

The Chairman, of behalf of the WG members, expressed manythanks to the Instituto de Investigaciones Marinas (CSIC) fortheir hard work and hospitality, and especially to Dr AntonioFigueras and the secretarial staff.

23

ANNEX 1

WORKING GROOP ON PA'l'HOLOGY AND DISEASES OF MARINE ORGANISMS

(Vigo, 23-27 April, 1990)

LIST OF PARTICIPANTS

•

Dr P van Banning

Mr D Bucke

Dr S des Clers

Dr C Couillard

Mr D Declerk

Mr A Figueras

Dr G Bylund

Dr S Helgason

Netherlands Inst. for FisheryInvestigations

IJmuidenNETHERLANDS

Ministry of Agricul., Fisheries & FoodFish Diseases LaboratoryWeymouthDorsetUNITED KINGDOM

Cent re for Environmental TechnologyImperial College8 Princes GardensLondonUNITED KINGDOM

Department of Fisheries and OceansInstitut Maurice Lamontagne850 Route de la MerMont-JoliQuebecCANADA

Station de Peche MaritimeAnkerstraat 18400 astendeBELGIUM

Inst~ de Investigaciones MarinasMuelle de Bouzas36200 VigoSPAIN

Institute of parasitologyAbo AkademiPorthansgatan 320500 Abo 50FINLAND

Institute of Experimental PathologyFish Diseases LaboratoryUniversity of Ieeland128 ReykjavikICELAND

Dr B J Hill (Chairman)

Ms B Hje1tnes

Dr F Baudin-Laurencin

Dr J McArd1e

Dr S McG1addery

Dr A McVicar

Mr J M Masso

Dr J Menezes

Dr 5 Mellergaard

24

Ministry of Agricul., Fisheries & FoodFish Diseases LaboratoryWeymouthDorsetUNITED KINGDOM

Institute of Marine ResearchP 0 Box 1870/72 NOrdnes5024 BergenNORWAY

Centre National d'Etudes Veterinaires etAlimentaires

Laboratoire de Pathologie des AnimauxAquatiques

B.P. 7029480 P10uzaneFRANCE

Department of the MarineFisheries Research CentreAbbotstownDublin 15IRELAND

Department of Fisheries & OceansMonctonNew BrunswickCANADA E1C 9B6

Dept of Agric. & Fisheries for ScotlandMarine LaboratoryVictoria RoadAberdeen AB9 8DBUNITED KINGDOM

lnst. EspanÖl de OceanografiaApdo 155236280 VigoSPAlN

Instituto Nacional de Investigacao dasPescas

Departamento de Aquacu1turaAvenida de Brasilia1400 LisbonPORTUGAL

Fish Disease LaboratoryRoya1 Veterinary & Agric. UniversityBü10wsvej 131870 Copenhagen VDENMARK

•

Dr E Mialhe

Dr H Möller

Dr G Olivier

Mr G Santiago

Dr J Thulin

Dr D Vethaak

25

IFREMERLaboratoire de Pathologie et de

Genetique des Invertebres Marines17390 La TrembladeFRANCE

Inst. für Meereskunde an der UniversitatKiel

Düsternbrooker Weg 202300 KielFEDERAL REPUBLIC OF GERMANY

Department of Fisheries & OceansHalifaxNova 5cotiaCANADA B3J 257

Instituto Espanol de OceanografiaCorazon de Maria, 828002 MadridSPAIN

Statens Naturvardsverk740 51 ÖregrundSWEDEN

Netherlands Institute for FisheryInvestigations

IJmuidenNETHERLAND5

26

ANNEX 2

WORKING GROUP ON PATHOLOGY AND DISEASES IN MARINE ORGANISMS

(Vigo, 23-27 April 1990)

TERMS OF REFERENCE (C. RES. 1989/2.34)

(a) compile and analyse the data in recent national reports onthe prevalence of disease in marine fish stocks in the NorthSea, Baltic Sea, and Irish Sea, and review the status ofsuch studies from areas usually not fully reported (e.g.Baltic);

(b) consider the first draft of the proposed ICESbooklet/training aids for identification and recording ofdiseases by non-specialists involved in sea-going surveys ofmarine fish stocks;

(c) consider proposals for further subjects for publication inthe Diagnostic Fiches series;

(d) review information on the current disease status ofmariculture in ICES member countries, with emphasis on newdevelopments and identification of trends;

(e) in conjunction with the Working Group on EnvironmentalImpacts of Mariculture, receive and discuss the draftcontributions (as specified in item 5.3 of the Working Groupreport) for the review of problems of medication inmariculture and consider preparation of areport forpublication;

(f) consider methods for diagnosis, prevention, and control ofthe emerging diseases in mariculture;

(g) receive areport on the analysis of Vibrio strains causingdisease in mariculture in different ICES countries anddiscuss vibriosis vaccination failures;

(h) receive a progress report on the proposed introduction ofgenetically-manipulated Crassostrea gigas into ChesapeakeBay to replace the recent losses of Crassostrea virginica •due to disease;

(i) review experiences on techniques to measureimmunocompetence, to use biomarkers, and to determinephagocytic activity as tools in biological effects studies.

27

ANNEX 3

WORKING GROUP ON PATHOLOGY AND DISEASES OF MARINE ORGANISMS

(Vigo, 23-27 April, 1990)

AGENDA

1. Opening remarks.

2. Terms of reference, adoption of agenda, selection ofrapporteurs •

3. lCES Statutory Meeting 1989: points of relevance to WGPDMO.

4. Diseases in marine fish stocks.

4.1. National reports for 1989.4.2 ICES/IOC Workshop on Biological Effects Techniques,

Bremerhaven, 12-30 March, 1990.4.3 North Sea Task Force4.4 Compilation and analysis of data on disease prevalence

rates in marine fish stocks in North Sea, Baltic Seaand lrish Sea [sub-group task].

4.5 Review of experiences with techniques to measureimmunocompetence as a biomarker of pollution effects:(a) Experimental studies (b) Field studies

5. Diseases in mariculture.

5.1 Review of current disease status of mariculture in lCESmember countries:(a) fish (b) molluscs (c) crustacea

6.

•

5.2 Emerging diseases and methods for their diagnosis,prevention and control [including slide workshop].

5.3 Vibrio strains causing disease in lCES member countriesand vibriosis vaccination failures.

5.4 Progress report on introduction of genetically­manipulated Crassostrea gigas into Chesapeake Bay fordisease control.

5.5 Review of problems of medication in mariculture.

Publications

6.1 Glossary of terms used in pathology.6.2 Diagnostic fiches.6.3 Proposed training guide for marine fish disease

surveys.6.4 Other possible publications.

7. Any other business.

8. Recommendations.

9. Approval of WG report.

~----------------------------------- - -- ---

28

ANNEX 4

RAPPORTEURS

Agenda item

1, 2, 3

4.1

4.2, 4.3

4.4

4.5

5.1

5.2

5.3, 5.4

5.5

6

7, a

Rapporteurs

A Figueras, J Menezes

G Bylund, H Möller

D Bucke, D Vethaak

S de C1ers, J Thulin

A McVicar, S Helgason

p van Banning, S Mel1ergaard

D Bucke, F Baudin-Laurencin

G Oliver, E Miahle

J McArdle, B Hjeltnes

D Declerk, C Couillard

A McVicar, S McGladdery

•

•

29. ,

ANNEX SSYNOPSES OF NATIONAL REPORTS ON DISEASZ PREVALENCE IN ~NE FIsa

STOCKS (1989)

Belgium (D Declerk) The Belgian disease surveys included abiannual (May and October) survey in the Belgian continentalshelf and an annual survey (August) of adult flatfish. Takingthe 1985-88 survey period as reference for the disease situationalong the Belgian coastal zone, during 1989 a slight increase wasnoted for skeletal deformities in dab, flounder and cod, and forfin erosion, there was a slight decrease in prevalence in dab andin plaice. Skin ulcers occurred at the same prevalence rate forall species examined, apart from an increase in cod (5.4\). Dueto the abnormally high water temperatures last October, theexpected cod population did not arrive. Of the cod examined (n= 75), there were high levels recorded for Ichthyophonus hoferi(13.3\) and liver anomalies (10\). The protozoan disease Glugeastephani in dab, plaice and flounder showed little differencesduring this period compared with 1985-88, but on the other hand,a decrease of lymphocystis in dab and flounder was noted. Asystematic bacteriological examination was carried out onflounder livers and 6.6\ found positive. A significant decreasein the Anisakis larvae in herring was noted.

Denmark (S Mellergaard) The overall impression was a decreasein disease prevalence in dabs caught in the German Bight andalong the Danish west coast. The decrease involved bothlymphocystis and epidermal papillomas. In the Skagerrak, anincrease in the prevalence of ulcerations was observed, probablydue to a marked increase in fishing intensity in the area. Inthe southern Kattegat, which suffered from oxygen deficiency inthe summers since 1986, the prevalence of lymphocystis andepidermal papil10mas are still increasing. Fishing . in a gridsystem at a station ca. 20 nm NW off Esbjerg revealed a verysharp delineation of a dab stock with a high prevalence of X-cellgil1 disease.

Federal Republic of Germany (R Möller) Routine monitoring ofcod and flatfish diseases in the North Sea and, of Anlsaklsinfection in Baltic herring was carried out. No noticeab1edifferences were found in comparison to former years. ,A yellowdiscolouration was recorded in dab, now identified by Scottishcolleagues as lipoma. The,causes for spleen liquefaction of codremain unknown.

Attention was drawn to the "Multi-Institutional Project on FishDiseases in the Wadden Sea", the results of which will bepresented before the end of this year. Within the frame of thisproject, the occurrence of external diseases had been studied in122,000 fish of different species. So far, results areavailable only for cod. "'fellow pest", alethal conditionconsidered to be caused by Flexlbacter spp. bacteria, occurredmainly in the estuaries of the Weser and EIbe rivers where codalso showed the lowest nutritional condition. On the otherhand, no clear regional differences were found in the occurrenceof skeletal compression which affected 4.9% of-the population ofyoung cod from the Wadden Sea. By statistical analysis, anormally grown and a compressed group of fish could be separated

30

by using the relationship of total length to head length as acriterion.

One year after the seal epidemie in the Wadden Sea,parasitological studies revealed a reduction for about one thirdin the infection prevalence of the main fish carriers of thenematode Pseudoterranova decipiens. Smelt (60%) and seascorpion (35%) were the most heavily affected among 20 fishspecies studied. Studies of the stomach nematodes of marinemammals confirmed harbour seal to be the main final host forPseudoterranova, and dolphin as the main final host for Anisakis.The primary intermediate host of Pseudoterranova remainsuncertain. Only one larva was found in 8,000 crustaceansexamined from the Wadden Sea. Laboratory studies revealed asignificant reduction in the swimming speed of smelt infectedwith Pseudoterranova crassus and of eel infected withAnguillicola in the swim bladder.

Finland (G Bylund) The general fish disease survey was focusedmainly on the northernmost parts of the Baltic Sea (salinity 0.2­0.4% 0) • lt was discovered that there was almost completeinfertility in the burbot population in that area.lnvestigations to find a reason for this phenomenon are inprogress in Finland as well as in Sweden.

As in previous years, high prevalences of skin ulcers wererecorded in flounders. A bacterial agent regularly found in theaffected fish is the subject of experimental investigation. Theresults indicated that we might be dealing with a new subspeciesof Aeromonas salmonicida. Additionally, a fairly highprevalence of liver changes (liver spots, liver nodules) recordedfrom flounder. Histological examination showed that in the mainthese changes were of neop1astic nature.

Netherlands (P van Bannin7 and D Vethaak) A long-termmonitoring programme for dJ.seases in flatfish (dab - Limandalimanda, and flounder - Platichthys flesus) in Dutch near-shorewaters, applying the protocols recommended by lCES, has beeninitiated as a continuation of the previous 5-year in-depthstudies. Although in 1989 spatia1 patterns of the variousdiseases recorded were 1argely in accordance with findings inprevious years, their prevalence levels were much lower comparedto those found at similar times and sites in 1988.

•

Recordings for base-line data in wild fish stocks were carriedout with 5 general stock assessment surveys in the south-eastpart of the North Sea (area: Dutch coastal waters, German Bight, eDanish coastal waters). Dab, plaice and cod were examined forgrossly visible anomalies and diseases. The recordings weremade at the end of the cold water period (February-Aprll), wlthflsh generally ln poor conditlon, and at the end of the warmwater perlod (October-November), with flsh generally in goodconditlon. Comparison of data for the foregoing years (1988 and1987) showed an increasing trend of prevalence of llver nodulesof dab and plalce. For the other diseases recorded, fluctuatlngprevalences were establlshed over the past 3 years in the areasmentloned, and no concluslons of clear trends could be drawn.

•

31

Norway (B Hjeltnes) has no programme of disease surveys in marinefish stocks. There have been some specific studies undertakento determine if pollution in the marine environment may have someimpact on the fish health. NIVA and The National VeterinaryInstitute has conducted a pilot study with the main goal to

'measure levels of PAR in wild fish off the coast of Karm~y. Thefish were also observed for abnormalities. Because of thelimited number of fish sampled no firm conclusion can be drawn.

Flatfish caught at four different sites in the Hvaler Archipelagowere analysed fOr content of organochlorine contaminants andpolyaromatic hydrocarbons. The area investigated revealedelevated levels of organochlorine contaminants in the selectedfish. Of the biochemical responses in the fish, the use ofcytochrome P-450-dependent activities (EROD) in the liver forenvironmental monitoring showed promising results.

Sweden (J Thulin) The study in the Bothnian Bay continued.Perch were found with a rather high prevalence of gill damages(24%) at one locality, whilst results elsewhere were similar tothose obtained last year. Parasitological examinations showedthat microsporidians in the gills and kidneys of perch and white­fish were much more common at the northern localities thanfurther south. The Fishery Board recorded ulcerations of cod inthe southern Baltie during August at prevalences between 0 and7.3% in the different catches (n = 26). During monitoringoutside the Oskarshamn nuclear power station, SW Baltic, a totalof 12,090 specimens' of fish belonging to seven species wereexamined for external signs of disease. Ulcerations were thedominant disease.

United Kingdom

(a) England and Wales (0 Bucke). Monitoring wild stocks offish for diseases included studies on sewage-sludge dump-sitesand other stations spread around the North Sea and Irish Sea.On the dump-sites the results of gross pathological conditions indab did not revea1 any differences in disease prevalencescompared with the reference stations (1,500 dab examined).Liver nodules in dab were not observed macroscopically; however,histological examination of livers of dab (>25 cm length size)revealed a 3.7% prevalence of pathological changes. On the morecomprehensive summer ground-fish survey (August/September)disease prevalences in dab were overall similar to those recordedin previous years. Six thousand dab were examined from 30stations spread over the North Sea. Highest disease prevalenceswere recorded off the Firth of Forth and on the Dogger Bank.Liver nodules were generally recorded at low prevalences, butwidespread with indications of higher prevalences on the DoggerBank. Studies on a dump site in Liverpool Bay (Irish Seal wererather inconclusive, with few fish being eaught on the dump-sitestation. Prevalences for diseases in dab on reference stationswere similar to those recorded previously. An ulcerative skincondition of cod, reported in 1988, continued to occur at a lowbut persistent level throughout the year. The aetiology has notbeen resolved. Visceral granulomatosis in cod was rarelyreported this year.

32

(b) Scotland (A McVicar). A repeat survey on sewage sludgedump grounds off the Forth, adjacent and distal reference areasand in the vicinity of an oil field showed no significantdifferences in the prevalence of Lymphocystis, skin ulcers andhyperplasia/papilloma in common dab. No general or localisedtrends in prevalence levels were apparent over 3 year's data fromthe same localities sampled by standardised methods. Ahypodermal lesion in dab, with significantly highest prevalenceoff east Orkney, was diagnosed as a multiple lipoma. Mature

. females were mainly affected. The prevalence of the Digeneanparasite Zoogonoides in Buccinum was significantly lower insampling areas close to asewage dump site compared with moredistal areas. Studies on the parasite system in the secondintermediate and final hosts in field and experimental conditionshave suggested decreasing trends in infection levels withincreasing levels of sewage concentrations. Intensive studiesof dab disease trends in relation to physical, chemieal,biological variables and seasonally have commenced on asewage •sludge dump site.

Other countries No significant studies on wild fish diseaseshad been carried out in 1989 by France, Ireland, Spain, Portugal,Canada and Iceland. However, for the latter country, surveysare planned in the near future. The Portuguese delegatereported a locally high (up to 30\) infection of sardine withKudoa, the enzymes of which make the flesh unmarketable if thefish cannot be cooled directly after capture. From Ireland itwas reported that there had been a collapse of the sea-troutpopulation along its west coast: the remaining fish obviouslysuffered from starvation. The situation has added to theconflict between local aquaculture and anti-fishfarming groups.

No reports were obtained from the East European countries or fromthe USA.

•I

33

.ANNEX 6

SYNOPSES Oll' NATIONAL REPORTS ON DISEASE STATUS IN MARICOLTORIl:

(a) FIN FIsa

Canada (G Olivier)

Vibrio salmonicida, the eausative agent of "Hitra Disease" oreold-water vibriosis has been identified in Atlantie salmon forthe first time in North Ameriea on the east eoast of Canada.The disease only affeeted one farm whieh experieneed ehronicmortalities in April and May 1989. Elsewhere, infeetiouspancreatic neerosis virus (IPNV) was isolated for the first timefrom Atlantie salmon in British Columbia, no mortalities wereassoeiated with this finding. Also on the west coast Vibrioanguillarum serotype 0-2 was recognised for the first time in1989, this finding may explain the eontinuing significant lossesattributed to vibriosis even in vaccinated fish. On both coastsbacterial kidney disease (BKD), vibriosis and furunculosis, asweIL as sea lice, continue to cause significant problems in thesalmonid aquaculture industry. Considered as a pressing problemis the syndrome of marine anaemia in chinook salmon on thePaeific eoast, a viral aetiology is suspected for this disease.

Denmark (5 Mellergaard)

Most of the Danish marine fish farms (rainbow trout) had one ortwo outbreaks of vibriosis and furunculosis; 40% of the rainbowtrout were vaccinated against vibriosis and furunculosis beforetheir transfer to seawater. Vibriosis observed in vaccinatedfish stocks was caused by the same serotype (Type 1) as the onein the vaccine. Several outbreaks of vibriosis was observed inelvers during the first week after arrival. A syndrome withunknown aetiology, Mred-head disease", in eels caused severeproblems.

Fin1and (G Bylund)

One main problem was the very rapid spread of furunculosisamongst the rainbow trout farms. The first few cases in the seafarms were recorded in 1988; during 1989 the disease wasrecorded from 26 farms. The baeterial strains isolated arefairly resistant to oxytetracyc1ine. Baeterial kidney disease(BKD) was recorded for the first time in Finland in 1989. Thedisease occurred in a cage farm with Atlantic salmon and rainbowtrout. The affected salmon were slaughtered out. As thedisease occurred in an area with intensive fish farming, it isexpected the disease will spread more widely. A project on theaccumu1ation and retention of antibiotics in fish farm sedimentswas carried through.

France (F Baudin-Laurencin)

Pancreatic disease was the most significant disease since anoutbreak in Atlantic salmon gave a 25% mortality rate. Again,this disease was also. ebserved in brewn treut. Most of thesalmonids were successfu1ly vaccinated against vibriosis, but thedisease gave a significant mortality in non-vaccinated juvenileturbot. A second pathogenic strain of Vibrio anguillarum was

34

identified in turbot in the south of the French Atlantic coast.New problems of unknown future significance were hepatic nodulesin Atlantic salmon and amuscular and visceral microsporidiosisin turbot.

Ieeland (5 Helgason)

Diseases of salmonids: Atypical furunculosis (Aeromonassalmonlclda subsp. achromogenes) has been detected in Atlanticsalmon and arctic char in 11 shore-based rearing facilities andone cage farm - a similar situation as the year before. Allsizes of fish from smolts to slaughter size fish and brood fishare affected. Disease symptoms vary. Fish may die withoutobvious lesions, but sometimes haemorrhage is seen in the eyesand at the base of the pectoral and pelvic fins. In moreadvanced cases, haemorrhage and blood-filled pustules and evenopen lesions develop. There are varying degrees of haemorrhagein internal organs. The frequency and severity of outbreaks •depends on various factors such as the quality of smolts, gradingtechnique and frequency, and the stability of environmentalfactors such as salinity and temperature. The outbreaks arealmost always limited to brackish water. Oxolinic acid and asUlpha-trimethoprim compound is generally used to controloutbreaks. Frequently, repeated treatment is needed. In 1989,the first antibiotic-resistant strain of A. salmonicida subsp.achromogenes was detected, Le. resistant to a sulpha­trimethoprim.

In 1989, bacterial kidney disease (BKD) was detected on four seacage sites rearing At1antic salmon and rainbow trout, compared totwo in 1988, and in returning Atlantic sa1mon to one sea ranch,compared to two in 1988. The two cases from 1988 had both thesame source of smolts, but the two new cases in 1989 were tiedtogether and could be traced to a new source of infection.Present1y there is insufficient information available regardingthe significance of this disease on the cage sites, because themortality is frequently associated with other factors such asskin lesions which develop during the coldest winter months.The initiation of these skin lesions may be mechanical damagecaused by lice (Caligus spp.) with subsequent rubbing in nets, orby mechanical damage of skin by nets in heavy seas, especiallywhen fish are crowded in cages. The healing of the wounds ishampered at .low temperatures and/or by low vitamin content,especially vitamin C, in wet food pellets, and by environmentalbacteria, such aso Vibrio spp. and Flexibacter spp., which easily

·invade the open lesions •. Occasionally, similar lesions developon fish in shore-based tanks. The initiation of these lesionsis likely to be due to the bad quality of smolts, grading of fish ~

and insufficient vitamin content of the food. ~

5ea lice, especially Caligus sp., are frequently a problem onfish in sea cages. Nuvan and Neguvon have been'used to controlthis problem. Sea lice have not been able to proliferate onfish in shore-based tanks, even in full strength seawater becausethe rearing water is either pumped through bore-holes or directlyfrom the sea at some depth. The lice will gradually die offfish when they are transferred from sea cages to tanks with full-strength seawater, without any special treatment. Most likelythe renewal of seawater is sufficient to wash all larvae out of

"35

the system.

Exophiala sp. was isolated for the first time in 1989 fromAtlantic salmon on 2 fish farms rearing fish in shore-basedtanks. lnfected smolts were transferred from one of the farmsto the other. The origin of infection is unknown. Theprevalence of infection is apparently low and no mortality hasbeen associated with this infection.

Diseases of halibut: As mentioned above, small wild fish havebeen caught at sea and transported alive to shore-based rearingtanks. Disease problems have been few and of minor importance.Mechanical damage of epithelial tissue which occurs duringcatching and transport may lead to open skin lesions and"subsequent death due to osmoregulatory failure. Favourableenvironmental rearing conditions, e.g. a layer of sand in tanks,aids the healing of lesions, but occasionally a bath treatmentwith a compound like flurnequine is needed. Parasites likeLepeophtheirus hippoglossi, Entobdella hippoglossi and Trichodinasp. have been isolated from newly caught individuals. Formalintreatment is efficient, but the overall effect of these parasitesis small.

Ireland (J McArdle)

Pancreas disease: This disease continues to be the most seriousdisease of farmed salmon in Ireland. About 15 sites wereaffected and losses due to the disease were severe, up to 80%losses in some instances. No disease agents have been iso1atedfrom affected fish. A major research project funded by the Eeis at present underway at University College, Galway. Like DAFSat Aberdeen, it seems they have had some success in transmittingthe disease. Good management practices appear to be importantin alleviating the losses.

Sea lice: Sea lice continue to be a significant problem at mostmarine salmon farms in Ireland. Lepeophtheirus sp. and Caligussp. are involved. The standard treatment continues to beDichlorvos. Because of pressure from environmentalists and thedifficulties in effectively treating the disease with this drug,newer treatments are being studied at University College, Galway.The use of Ivermectin is showing some promise and trials haveshown that lice can be very weIl controlled by this drug.However, further work on residues and environmental effects arerequired.

Furunculosis: This continues to be the most important bacterialdisease of farmed salmon in Ireland. A number of sites wereaffected in 1989. Problems of antibiotics resistance have begunto emerge, in some cases mUltiple drug resistance. Trials usingcommercial vaccines were commenced at one site last year and someimmunity appears to have been conferred following use of aninjectable vaccine. A "relative percentage survil (RPS) of 68%was the level of protection achieved.

Emerging disease problems: An intra-erythrocyte inclusion-typevirus was detected in fish at one farm which was associated withmortality.

which resembledand resulted in

36

Actinobacillus-like disease: A diseaseactinobacillosis was observed at one farmsignificant losses was detected at one farm.

Norway (P van Banning)

Bacteria: Furunculosis has had a significant spread amongseawater fish on the west coast of Norway and is continuouslyspreading to new areas. The most likely way of spread has beenthrough water. The frequency of Yersiniosis has been reducedsignificantly and is no longer a problem of any significance infish farms in Norway. V. vulnificus infection in farmed eel andNocardia infections in Atlantic salmon were detected for thefirst time in 1989.

Viruses: Infectious anaemia in Atlantic salmon (ISA) has nowbeen detected in about 80 farms since its first description. Inaffected fish, two virus particles with a size of approximately •80-90 nm have been detected in red blood cells. Thesignificance of these virus particles is still to be determined.There seems to be an increase in the number of cases of clinicalIPN in Atlantic salmon and IPN virus has been isolated frommoribund turbot and halibut fry. Erythrocytic inclusion bodysyndrome virus (EIBSv) has been detected in Norway for the firsttime.

Parasites: Salmon lice is still the major parasite problem.Trials with a new compound (pyrethrum) have shown promisingresults. Gyrodactylus salaris has been detected in twoadditional rivers. Hexamita salmonis and Gyrodactylus bykowskiihave been reported found on Atlantic salmon in seawater.

Portugal (J Menezes)

Concerning finfishes, mariculture is not yet very significant.Nevertheless, in some coastal areas, artisanal polyculture hadsocial economic interest; however, about 50\ of farmed finfishes

,were mullets that are (for the time being) low-price marketablespecies. After 1986, considering the availability of EEC/FEOGAfunds, 71 projects were submitted, concerning main1y sea bass,gilthead seabream, salmon, turbot and eel (as weIl as kurumaprawn, clam and sea scallop). The approved projects, including2 hatcheries, are almost in full operation. The majority offinfish cultures are low semi-intensive units in earth pondsimproved from artisanal polycultures and from inactivated saltbasins. The two hatcheries, two intensive salmon farms, andsome semi-intensive fish farms (sea bass and gilthead sea breamthe target species) are in process.

This preliminary information allows an understanding of theknowledge of the actual health status of mariculture in Portugal.Indeed, a high number of potential pathogens in cultureconditions were identified which allowed the implementation ofprophylactic measures. Among them are conspicuous parasiticdiseases like sea bass argulosis and diplectanosis of skin andgills. The importance of, prophylaxis, including the adequatemanagement implementation, is emphasised.

··e,

37

Spain (A Figueras)

Since 1983, Vibrio anguillarum continues to be the main causativeagent of epizootics in small turbot «20 g). Serotypes 01 and02 of this species have been isolated. Since 1986, vibriosclosely related to V. anguillarum (V. splendidus and V. pelagius)have been implicated in mortalities of all cultured fish speciesin the Atlantie eoast (turbot, Atlantic salmon, Pacific salmonand rainbow trout) affecting both juveniles and adult fish. Onsome oecasions, these vibrios were isolated from turbot inassoeiation with viral infections. Vibriosis eaused by V.vulnificus biotype 2 was only notified in European eel culturedin the Mediterranean coast and represents the first descriptionof this species in Spain. Other vibrios, V. fischeri and V.harveyi, were isolated from turbot in sporadic cases associatedwith mixed pathologie syndromes (i.e. parasites, tumours).

Septieaemia by aeromonads (Aeromonas hydrophila and A. sobria)caused low and continuous mortalities in European eel, affectingall sizes. In sea bass cultured on the Mediterranean coast, anEdwardsiella sp. has been isolated for the first time, whichcaused the mortality of practically all the fish stock.

The drugs routinely administered to farmed fishes for controllingthe majority of bacterial infections are oxytetracycline,oxolinic acid, flumequine and nitrofuranes • Whereas, the V.anguillarum strains isolated on the Atlantic coast were sensitiveto oxytetracyeline, an important number of V. splendidusimplicated in turbot mortalities showed their resistance to thisantibiotie.

Until now, the viral infections in farmed fishes in marine watersdid not represent important economie losses • In culturedturbot, only an Irido-like virus has been isolated in assoeiationwith V. splendidus from an haemorrhagic syndrome which producedlow mortalities in adult fishes. viral erythrocytie necrosis(VEN) was only reported in sea bass, affecting both cultured andwild populations which appear to be becoming more susceptible tobacterial infections.

Fishes with external symptoms similar to pancreas disease wereobserved for the first time in 1989 in Atlantie salmon importedfrom Ireland. Parasitation of turbot by Bothryocephalus will bean interesting topie to study in the next years.

Sweden (J Thulin)

Two serious infectious diseases, furunculosis and BKD, havespread considerably, the latter one with over 60\ increase sincelast year. The diseases are spread mainly by transport ofliving fish and eggs. Regarding furunculosis, the white-fish(Coregonus spp.) is also a suspected vector. The infectiousdermatitis (ASA) has been recorded in 58 farms in different partsof the country and two new cases of Yersiniosis have occurred.Finally, a disease similar to the Norwegian infectious salmonanaemia has been recorded to occur in rainbow trout.

38

Onited Kingdom

(a) England and Wales (0 Bucke)

Significant numbers of fin-fin are not eultured in the marineenvironment in England and Wales and no major disease problemshave been observed.

(b) Scotland (A McViear)

Atlantie salmon: The salmon farming industry in Seotlandeontinues to grow with the 1989 production being 28,553 tonnes (a58% increase from 1988). A trend in decreasing survival ratesfrom smolt to harvest has continued with only 2 out of 3 fish nowsurviving. This and the lowest ever recorded mean weight forharvested salmon has been attributed partieularly to disease andis not solely due to management and marketing deeisions. Theindustry is responding by introducing area management plans wheredifferent companies with loeal interests co-operate and by ~

reducing maximum stoeking densities in cages. Furuneulosis •continues to be an inereasing problem, particularly with strainsshowing multiple antibiotie resistance. Trials are in progresson a new vaccine. There are indieations of increasing toleranceof sea lice to Dichlorvos and alternative compounds andstrategies, e.g. vaccination, cleaner fish are beinginvestigated. Increased research effort is being directed intothe infectious cause, prevention and control of pancreas diseasewhich shows a gradually increasing prevalence in the industrywith direct and indireet economic effects.

A new problem first reeognised in 1988, and apparent again in1989, was "fading smolt syndrome" where post-smolts having grownweIl after seawater transfer. There is no evidence of infectionbut at present the aetiology is unknown.

(b) SHELLFISH

Canada (S MeGladdery)

This year, a previously undescribed protozoan parasite was foundin the connective tissue of broodstock bay scallop (Argopectenirradiansl. This parasite elieited a strong hyalinoeyteeneapsulation response, but was only readily detected, usinghistology, in adult scallops. It appears to be transmitted fromthe broodstock to the spat generation, although transmissionstudies are ongoing. It produced Lugol-positive spores afterineubation in fluid thioglycollate, henee the tentativedeseription as Perkinsus-like. So far, this parasite has not abeen detected in indigenous bivalves, although field surveys are ..,continuing. The known occurrence of what appears to be the sameparasite in bay scallops from Rhode Island and Cape Cod suggeststhat it may have been introduced with the original bay seallopstock in the late 1970s at an undetectable level. Extensivequarantining to the 7th generation, however, failed to revealthis parasite at that time.Recently, a die-off of quahog (Mercenaria mercenarial spat at anexperimental shellfish hatchery revealed massive inflammation,hemocyte necrosis and what appear to be gregarine gametocytes.

39

Work on the identification and epidemiology of this paras1te isjust starting.

France (E Miahle)

Marteilia refringens/Ostrea edulis. In relation to aparticularly hot summer, several Martel1la outbreaks wereobserved in different areas (west and south Britanny, ArcachonBasin). The high prevalences, noticed in Rade de Brest, led toblock transfers to Cancale. Thus, marteiliosis continues tolimit flat oyster production, especially in rivers and bays.First experiments have shown that O. puelchana is sensitive tothis parasite.

Bonamia ostreaelOstrea edulis: The disease prevalence wasrelatively high in all the flat oyster production areas. Goodresults were obtained in deep waters where there were low spatdensities. Several comparative assays are in progress fordifferent spat origins (Mediterranean, Atlantic). Experimentalstresses (mechanical, emersion) have been applied to establishtheir effect on bonamiasis development. Complementaryexperiments are being conducted to determine the best times foroyster transfers. Concerning Bonamla diagnosis, it is nowimportant to indicate the reliability and suitability of theELISA kit, which has been tested by teams in different countries.In the case of large epidemiological surveys at the Europeanscale, this qualitative and quantitative assay is more efficientthat light microscopy because it is better adapted for largesampies and equivalent in sensitivity. In order to have a verysensitive method in fundamental research for Bonamla diagnosis,the parasite's DNA was cloned and restrictive fragment sequencingis in progress for PCR application •

. Rickettsia sp.IPecten maximus: A gill rickettsia, observed in1986 in several Pecten maximus beds, is now putatively related tothe scallop mortalities on the basis of epidemiological surveysand physiopathology analyses. The procaryote appears non­transovarially transmitted and experimental horizontal infectionswere successfully performed with purified rickettsias. In thefield, scallop spat become quickly infected. Preliminaryexperiments suggest a positive effect at first rearing time (3-6months) in non-infected areas (e.g. Mediterranean) , since suchyoung scal10ps are significantly less infected than controlanimals after several months in the same infected area.Complementary experiments will be performed.

Vibrio sp. (Pl)IRuditapes rhi1ippinarum: After a serious nationaloutbreak of brown ring d1sease, the situation has eased becauseof the elimination of infected stocks and by the possiblebeneficial effect of high summer temperature.(Vlbrl0 PI issensitive to temperatures above 30'C when exposed for a fewhours). Moreover, a treatment was devised for decontaminationof young scallops, applied when leaving the nurseries(Furazolidone, 10 ppm, 3 x 24 h). Other bivalve species incontact appear non-sensitive to Vibrio PI' .

Perkinsus sr. IR. philippinarum: Perklnsus sp. 1s a1ways observedin R. phil~pplnarum populations, but the prevalences are always

very low.

40

NO mortality was related to the parasite.

Crassostrea gigas: A collaborative study (France/USA) is beingconducted on oyster velar irido-virus, which is ultrastructurallysimilar to LDV. In order to try to obtain suitable reagents forepidemiological studies in larval populations, a set ofpolyclonal and monoclonal antibodies for LDV has been prepared.

In collaboration with S Bower, serological comparisons betweenB. ostreae and Denman Island microcell were performed, leading usto totally distinguish the parasites. DNA probes, specific forB. ostreae, will also probably be tested.

Germany (H Möller)

No information is available on the disease status of the oyster,Crassostrea gigas and the musseI, Mytilus edulis, cultured alongthe German North Sea and Baltic Sea coast. However, aveterinary authority is conducting microbiological and chemicalstudies on a regular basis on the occurrence of pathogens, algaltoxins and pollutants potentially harmful to human consumers.

Ireland (J McArdle)

No disease outbreaks reported.

Nether1ands (P van Banning)

The protozoan oyster pathogen Bonamia ostreae has spread in 1989through the central part of the Dutch oyster area Grevelingen.Only the oyster stock of the eastern and western part of theGrevelingen was still free of Bonamiasis. In the central partof the Grevelingen, Bonamiasis reached in the autumn (September­November) a prevalence range of 6-8\ in the wild oyster stock,and a prevalence range of 2-46\ in the commercial oysterplantings. For management purposes, a special researchprogramme was started to check the possibilities for continuationof a commercial oyster production under the recently developedstatus of Bonamiasis in the Grevelingen. The results of thisresearch programme showed that in the oyster growing season of1989 the Bonamiasis prevalence increased from a range of 2-8\ inJune to a range of 20-40\ in October. Morta1ities due toBonamiasis reached in October/November a prevalence range of20-47\ in the management research programme and a range of 6-80\in the commercial oyster plantings. The results of theBonamiasis research of 1989 revealed that planting densities ofoysters and different fishing or planting techniques are of noeffect on the development of Bonamiasis. However, environmenta1circumstances ruling the physiological status of the oysters(e.g. temperature and depth of an oyster areal and stress­inducing factors (e.g. fishing and rep1anting of oystersl have aboosting effect on the development of Bonamiasis.

Norway (B Hjeltnes)

A new screening programme has been started for contro1 of thehealth and parasite status of bivalve molluscs in commercialproduction. Broodstock population of oysters and clams used inhatcheries and lagoons are the primary subjects of investigation.No . pathogenic agents (Bonamia, Marteilia, Perkinsus,

41

haplosporidia, etc) have so far been detected.

Portugal (J Menezes)

In Portugal up to 1986, mariculture social economic importancewas related to clam, Ruditapes decussatus, production in A1garve(south coast) representing about 73% of total Portugueseaquaculture production. It is important to underline that 20years ago, Tagus and Sado estuaries (near Lisbon) produced around20,000 metric tonnes of Portuguese oyster, Crassostrea angulata,being now almost nil due to environmental degradation after non­controlled industrial development (shipyard, chemicals,pesticides, etc) and opportunistic pathogens that foundsuitability in debilitated animals. The cu1ture of othermolluscs, like mussei, flat oyster and crustacea, was very sma1lor absent.

Spa1n (A Figueras)

Culture of the flat oyster is almost non-existent. The mainactivity is based on the importation of flat oysters from a11over Europe: the most important providers are Greece, Turkey,Italy, Yugoslavia and England. Bonamia is present in Galicianwaters and cumulative mortalities reaeh 80-90\ by the end of,theseeond year. The health status of the imported oysters is notmonitored, although there is astriet regulation on imports andquarantines because the volume·of the merchandise is such that itis almost impossible to control the disease. In a study carriedout with native oysters, Bonamia ostreae had the highestprevalence at the end of the culture cycle with values of 80%.During the year of 1989, the monthly mortality rate reached 30%in the experimental culture trays.

The most valuable species of clams is Venerupis decussatus. Oneof the most important providers of clams is Portugal where aPerkinsus-like organism causing mortalities has been detected.This organism has been detected also in c1ams imported into Spainand held, as is ruled by law, in depuration plants. Severemortalities were detected. In November 1987' another mortalitywas detected in several depuration plants. The histological

'examination revealed the presence in 50% of the 30 animalsexamined had plasmodial stages of an Haplosporidium similar tothe one described by Chagot et al. (1986) in Portuguese clams anda Perkinsus-like organism. A study is being carried' out toclarify which of the two parasites could be causin§ thesemortalities. The same parasites have been detected in culturedclams from the south of Spain. Attention should be paid tothese parasites, keeping in mind the Marteilia and Bonamiaexamples in the Ostrea edulis culture in France. A monitoringexperiment has been carried out during the year 1989. Mortalityrates could not be followed. The prevalences of Perkinsus sp.,tested using the thioglyco1late method, reaehed 30%. Right'nowthe prevalence of Perkinsus sp. and of the Haplosporidium sp. isbeing studied. The first results show a prevalence of around30% for both parasites.

There have been importations of Manila clams (Venerupis semi­decussatus) from France showing signs of what 1s called "brownring disease". No morta1ities were detected, nor was thesyndrome found in the areas where these species of elams are

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cultured (mainly the south of Spain). In Andalucia, clams ofthe same species have been found with a similar type of browndeposit in the internal part of the shell, but no mortalitieswere detected. A bacteriological study made with samples ofclams with and without the syndrome showed the presence ofseveral strains of Vibrio sp.

Mortalities of cockles (Cerastoderma edule) have occurred indepuration plants. The relationship between the presence ofparasites and the mortalities is not clear.

In the case of the mussel culture, although several parasites andhistopathological conditions have been detected there have beenno mortalities at all. Mussel growers complain that duringsummer the mussels must be handled with a lot of car becausethere is an important death rate. This, if true, could beattributed to the cOmbination of double and triple infectionswith different parasites (Marteilia maurini, ciliates and theparasitic copepod, Mytilicola intestinalis) and adverse ~

environmental factors such as high temperatures. Mussels have ~

an advantage in that there is almost no time available for thedevelopment of a strong infection, since they reach thecommercial size (7-9 cm) in less than 18 months.

United Xingdom (0 Buckel

Bonamia in Ostrea edulis remains the only problematic disease inrelaid molluscan stocks. Where stocks were relaid under MAFFguidelines prevalence levels of the disease were kept below 10\after one growing season.

Gaffkaemia was confirmed as the cause of substantial losses (upto 20% per day) of Homarus gammarus stocks held in 3 holdingsites on the south and west coasts during the summer months.The cases could be tentatively linked imports of North Americanlobsters. Sites were emptied and the holding facilitiesdisinfected.

U.S.A. (E Burreson)

After 4 years of drought, 1989 was a year of above-averagerainfall for the eastern United States. The resulting lowsalinity greatly reduced the preva1ence and intensity ofHaplosporidium nelsoni (MSX) in oysters along the Atlantic coast,including Oelaware Bay and Chesapeake Bay. This disease was nota source of significant oyster mortality in most areas during1989. Unfortunately, the decreased salinity has little effecton Perkinsus marinus in the Chesapeake Bay. This parasitepersisted tenaciously on all oyster beds in Virginia and mostbeds in Maryland and caused mortality in areas where salinity was ~

above about 12 ppt during summer." Oyster production in Virginia ...declined to arecord low 209,605 bushels in 1989 as a resu1t efthe combined effects of the twe diseases and continued fishingpressure. There have been no reports of new diseases orsignificant changes in the status of other, less important,shellfish diseases.