Annex A, and on other emerging fish diseases, forms the basis of this paper. The production of .... (SVC), Bacterial Kidney Disease (BKD). (Renibacterium ...
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 72
Finfish in aquaculture and their diseases – A retrospective view on the European Community. E. Ariel and N.J. Olesen EU Reference Laboratory for Fish Diseases, Danish Veterinary Laboratory, Hangøvej 2, DK-8200 Århus N
Abstract Results from annual surveys since 1995, in the European Union (EU) and some neighbouring states on the epidemiological situation of fish diseases listed in Council Directive 91/67/EEC Annex A, and on other emerging fish diseases, forms the basis of this paper. The production of cultured finfish is expanding in EU. From 1995 to 2000 total aquaculture production increased 60% to approximately 520 000 tonnes in 2000. The traditional emphasis on rainbow trout (Oncorhyncus mykiss) and salmon (Salmo salar) production shifted during those years to include other species – of particular mention are seabream (Sparus aurata) and seabass (Dicentrarchus labrax) in the rapidly growing Mediterranean aquaculture industry. ISA entered the Community in 1998, but appears to have departed again after prompt implementation of control measures given in Council Directive 93/53/EEC, thus regaining its status as an exotic disease in EU. The ongoing efforts of surveillance for notifiable fish diseases on list II, and the associated ensuing trade regulations between approved and non-approved zones have in most cases successfully contained those diseases. The trend is for an increasing number of zones and countries to move towards approval for freedom of notifiable diseases.
Introduction The projected shortfall in fish supply by year
Despite these strategies for sustainable expansion of aquaculture, disease outbreaks remain
2010 (FAO) is unlikely to be met by traditional capture fisheries sources. Aquaculture on a
a considerable obstacle to aquaculture production and development (Subasinghe, 1997).
global scale has the potential to meet the challenge of food supply to the increasing human
Disease may cause direct losses to the industry and prevent its potential expansion, but
population (Rana, 1997). Without jeopardising conservation and management of
further ramifications include shortage of food, jobs in rural areas as well as social and envi-
biodiversity, an expansion of aquaculture production under the FAO code of conduct for
ronmental costs especially for low-income food deficit countries (LIFDC) (Subasinghe,
responsible fisheries, could include the exploration of the use of under-exploited species
1997). Keeping in mind that “Prevention is better than Cure” and likely also more cost-
for human food, multiple species culture, sustainable harvest at multiple trophic levels and
effective, it is most important that preventative measures against introduction of patho-
a reduction of post-harvest losses (Kyoto Protocol).
gens into the fish culture environment is
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 73 of the internal market of the European Union, efforts have been made to contain certain diseases. Data relevant for aquaculture including production, organisation and the regional disease situation has been collected annually by each state since 1995. On this basis the Community Reference Laboratory attempts to obtain an overview of the epidemiological situation of fish diseases listed in Council Directive 91/67/EEC annex A and on other emerging fish diseases. Of special interest to the survey are the List I disease infectious salmon anaemia (ISA) and List II dis-
Figure 1. Countries contributing to the year 2000 survey on VHS and IHN in the community. Member states are dark grey, with neighbouring participating states in light grey.
prioritised. To contain pathogens in infected areas it is therefore necessary to identify where they are and where they are not. To this end, veterinary and sanitary services of each region have to co-operate and update each other as well as provide standardised health certification and quarantine services to those farmers, who may wish to trade in live aquatic animals. In 1995, aquaculture production in Asia accounted for over 90% of world output (Tacon, 1997), the majority of which was produced by China (Rana, 1997). FAO and the Network of Aquaculture Centres in Asia-Pacific are collaborating with government agencies of the region to implement a strategy for regional quarantine practises (Subasinghe, 1997).
eases viral haemorrhagic septicaemia (VHS) and infectious haematopoietic necrosis (IHN). VHS and IHN mostly feature in rainbow trout at fluctuating temperatures below 15∞C whereas ISA is primarily associated to the cultivation of Atlantic salmon. In terms of target species and environment, these diseases are of most economic concern to the northern countries. In the southern part of Europe, Viral Encephalopathy and Retinopathy (VER; VNN, Nodavirus infection) are a repeated nuisance of late in the seabass industry. This paper reports on the trends in European finfish culture since 1995, it deals with the zoning of individual countries with respect to the notifiable diseases VHS and IHN and briefly covers the pathogens presently of major importance to aquaculture. Attempts are made to put this information into global context
Survey participants and procedures
Continental Europe produced a mere 5% of
The data collected annually by the National Reference Laboratories (NRLs) are submitted
total world aquaculture in 1995 (Tacon, 1997), however, trade regulations has a long stand-
to the Community Reference Laboratory for Fish Diseases (CRL) where it is collated, ana-
ing history in this area and with the opening
lysed and disseminated back to the partici-
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 74 tries, the format of the questionnaire has been
300
100 tonnes
250
ter clarify their specific situation and thus al-
200
lowing for a more realistic comparison.
150
Aquaculture in Europe has been compared to a patchwork quilt and several factors contrib-
100 50 0
Austria
Denmark
Greece
ute to its versatility: The temperature regimes vary a great deal between the northern and
Figure 2. Distribution of farms in production size category in year 2000.
southern parts, from icy waters in Northern Scandinavia to bathtub temperatures in shal-
pants. In addition to Member States, several
low Italian marsh ponds. In terms of salinity, mariculture is the name of the game in Scot-
neighbouring countries have contributed to the survey: Norway, Iceland, Switzerland, Czech Republic, Slovenia and lately also Poland, Bosnia-Herzegovina and the Faeroe Is-
land and Greece for example, whereas Austria is represented by the freshwater alterna-
lands (Figure 1).
tive only. Local traditions too play a part in how aquaculture is perceived. On the Italian
The questionnaire consists of 3 sections: Gen-
Adriatic coast, man-made marsh ponds have been stocked with wild-caught fingerlings for
eral data, epidemiological data and laboratory examinations. The first section is concerned
centuries, to be harvested after a minimum of input into the system. In Germany, small
with zone status, survey programmes, production data and farm details. The epidemio-
hobby farms with fish for private consumption is a common feature. Even further north,
logical section covers the situation regarding the notifiable diseases VHS and IHN on list
the Scottish salmon industry has changed traditions and embraced intensive culture where
II. The last section pertains to laboratory capacity and recently identified pathogens.
every step of the process is studied, monitored and adjusted to optimise production in sea-
Based on the data from the questionnaire, the following account will summarise the devel-
cages. Different scales of operation are also important in the dynamics and internal commu-
opment of finfish production in EU since 1995, cover the past and current situation of list I
nication of the industry. In Austria, the majority of farms produce less than 5 tonnes per
and II diseases and briefly discuss other potential disease problems facing the
annum; in Denmark, most farms produce between 5 and 100 tonnes; and in Greece, the
aquaculture industry.
biggest proportion of farms is in the ‘more than 100 tonnes’ category (Figure 2). The fish
High diversity makes comparison difficult The configuration of the aquaculture industry in each country is unique and at times the comparison of one system with the other proves rather impractical. Over the years of collecting information from individual coun-
species chosen for culture in an area is dependent on the above factors and the suitability of available species. The specific diseases associated with finfish is also a sum of the above.
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 75 600000
1995 1996 1997 1998 1999 2000
500000 400000 300000 200000
larger slice of the pie called the total European production (Figure 4). Other countries have enlarged their production in step with the general trend and have thus managed to retain their relative part of the total production. In terms of species cultured, trout has consist-
100000 0
years, which in return has earned them a
EU
Norway
Figure 3. Total finfish production (t) in EU and Norway from 1995-2000.
Aquaculture production in Europe While taking the variation in the composition of the industry between countries into account, valuable information can be extracted from this extensive data-set, yearly and retrospective, within each country and between the different states.
ently, although on a declining note, accounted for the majority of the finfish produced in Europe (Figure 4). However, the proportion represented by salmon is increasing, which is likely linked to the Scottish expansion in this area. Other species, especially those cultured in Mediterranean waters, are also gaining importance on a European level. This is to a large degree associated with the recent strengthening of Greek mariculture of seabream and seabass .
The total production within EU has steadily increased from 323 000 tonnes in 1995 to 520
Although Europe is a small player on a world scale (5%), it is the biggest producer of cer-
000 tonnes in 2000 (61%). This tremendous increase is matched by the Norwegian pro-
tain products. EU thus accounts for 54% of the global aquaculture production of trout,
duction, which increased over 100% in the same period to 475 000 tonnes in 2000 (Figure
99% of European Eel (Anguilla anguilla), 68% of seabass/seabream and 100% of the turbot
3). Scotland, Greece and Spain have likewise undergone quite a development during these
(Scophthalmus maximus) production (MacAllister Elliott and Partners Ltd, 1999).
catfish carp other eel turbot sea bass sea bream
salmon
catfish carp other eel turbot sea bass sea bream
82,000 219,000
trout
233,000 147,000
salmon
1995 Figure 4. Total production (t) distributed on fish species in 1995 to 2000.
2000
trout
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 76
Netherlands Sweden Austria England Belgium Ireland Scotland Finland 75,000 Greece Spain
Netherlands Austria Sweden Portugal England Belgium Ireland Finland Scotland 75,000 Greece
65,000 France
65,300
Spain
Denmark
67,200
Italy
Denmark
Germany
1995
Italy
France Germany
2000
Figure 5. Total production (t) distributed on countries in 1995 and 2000.
Disease categories
Individual countries may obtain additional
All fish diseases of potential economic importance, which are restricted to defined regions
guarantees for import control, if they can document a survey and control programme
and are possible to control are categorised in list I, II or III, according to criteria outlined in Annex A of Council Directive 91/67/EEC
for diseases on list III. Currently there are six diseases on list III: Infectious Pancreatic
“placing on the market of aquaculture animals and products”. Thus, list I is for diseases exotic to the EU, and should they once appear, eradication must be attempted according to Council Directive 93/ 53/EEC “introducing minimum Community measures for the control of certain fish diseases”. Presently there is only one disease on
Necrosis (IPN), Spring Viraemia of Carp (SVC), Bacterial Kidney Disease (BKD) (Renibacterium salmonaris), Furunculosis (Aeromonas salmonicidae), Enteric Redmouth Disease (ERM) (Yersinia ruckeri) and Gyrodactylus salaris infection. List III is currently undergoing a revision and may even be deleted in response to a demand for simplicity in Community trade regulations.
list I: Infectious Salmon Anaemia (ISA).
The lists have not been reviewed since 1991
List II comprises those diseases, which are
and a number of diseases have emerged in the meantime (Streptococcosis (Lactococcus
restricted to certain locations, and are possible to control. Regions with approved freedom for list II diseases are obliged to restrict trade with regions of lower status. VHS and IHN are listed on list II. Control measures for list II diseases are likewise outlined in Council Directive 93/53/EEC.
garviae), Viral Encephalopathy and Retinopathy (VER) and Epidermal Ulcerative Syndrome (EUS)). The international trade regulations have gained an increased focus with Office Internationale des Epizooties (OIE) as a central partner in the World Trade Organisation (WTO). This has created a rising pres-
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 77 sure on EU to synchronise regulations with
similarity between the Scottish and Norwe-
the OIE guidelines as outlined in the International Aquatic Animal Health Code (2001) and
gian strains and less between the Scottish and Canadian. The small genomic variation to the
the Diagnostic Manual for Aquatic Animal Diseases (2000).
Norwegian strains, indicate that these viruses may have a common ancestor, possibly in wild Atlantic stock (Stagg et al. 2001).
List I diseases Infectious Salmon Anaemia (ISA) 1984 in Norwegian salmon culture (Thorud and Djupvik, 1988). In the nineties, there was
List II diseases Viral haemorrhargic septicaemia (VHS) and infectious haematopoietic necrosis (IHN) Zone status
a significant reduction in the number of outbreaks following implementation of a firm
The Commission will approve freedom for a notifiable disease in a given zone on the basis
control policy by the Norwegian Authorities (Håstein et al., 1999). In recent years, however,
of survey data only (Council Directive 91/67/ EEC and Commission Decision 2001/183/
the number of new outbreaks in Norway has increased (Håstein, Pers. Comm. 2000). The
EC). A country may apply for approval status for a zone after a compulsory period of 4
disease was restricted to Norway until 1996, when it emerged in Canada. ISA has now been
years with periodic testing of all farms with susceptible species. An individual farm in a
diagnosed in all major salmon producing countries, including Chile, USA, Canada, the
non-approved zone can also apply for approval status after completing the compulsory
Faeroe Islands and Scotland.
testing-scheme, if it complies with requirements for water supply and preventative
ISA is a disease of salmon, which emerged in
The first outbreak in the European Union was registered in Loch Nevis, Scotland in 1998 (Rodger et al., 1998). From there it presumably spread via movement of stock, people or equipment to 11 other salmon farms. The Scottish Authorities were intent on managing the disease according to provisions outlined in Council Directive 93/53/EEC during which several risk factors were identified and addressed in the management of Scottish farms. These measures were apparently successful and only 1 outbreak was registered in 1999
measures. A certified laboratory must carry out the testing for freedom of the diseases in question. Should the presence of the disease be diagnosed in any one approved farm, then that farm and all farms downstream are considered infected. The non-approved status will persist until that time that the farms have eradicated the disease by approved stampingout procedures and successfully completed the 4-year testing programme with new stock. Non-surveyed zones are regarded as infected.
and none in 2000 and the better part of 2001. Based on the success of the control pro-
In Austria, Belgium, the Netherlands and Greece, there is no survey programme in place
gramme, ISA will most probably remain on list I as a disease exotic to the Community.
to cover the farms. A single farm in each of Austria, Belgium and the Netherlands is ap-
Genetic comparison of isolates revealed a high
proved free of VHS and IHN. Greece is con-
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 78 sidered to be free of VHS, based on historical
Bretagne and Poitou Charentes provinces in
evidence and non-compatible temperatures. However, there is no survey in place to prove
France are zones approved free of VHS and IHN (203 farms in total in these zones). There
this and Greece therefore remains non-approved and cannot export susceptible species
are 15 additional farms approved free of both diseases in Adour-Garonne (6), Artois-
alive into approved zones. Portugal is in the process of applying for approval of freedom
Picardie (2), Loire-Bretagne (3), Rhin-Meuse (2), Seine-Normandie (1) and Rhone-
for list II diseases.
Mediterranee-Corse (1). A single farm in Artois-Picardie maintained its status as ap-
Approved farms and zones in Europe United Kingdom, Ireland, Sweden and Fin-
proved free of VHS after an IHN outbreak.
land are approved free of VHS and IHN in continental zones. At present, Italy is consid-
The provinces of Asturias, Galicia, Aragon, Navarra, Castilla y Leon and Cantabria in
ered to be endemically infected with VHS and IHN in most areas excluding 19 approved
Spain are approved zones with regard to IHN and VHS. Certain areas within the provinces
farms in non-approved zones and 10 farms in micro-zones in the Trento province. Farm-
are considered buffer zones and are therefore not approved. There is one approved farm in
ers in the rest of the country seem to lack the economic incentive for implementing survey
such a non-approved zone in Aragon.
and control programmes. As most suseptible species are consumed locally, and warm water temperatures prevent outbreaks of VHS and IHN, there is no need to certify freedom of those diseases. Germany has obtained approval for 2 zones regarding freedom of VHS and IHN in BadenWurttemberg in addition to 75 approved farms in non-approved areas. The farms are in Lower Saxony (9), Thuringia (5), BadenWurttemberg (52), North Rhine-Westphallia (4), Bavaria (3) and Saxony (2). Although an increasing number of registered commercial German farms are obtaining approval, those small hobby-farm operations with only one little pond for private consumption in certain parts of Germany, are harder to survey and control in terms of stamping out and movement of stock between zones.
Denmark is approved as continental and coastal zone free of IHN. It is also approved free zone for VHS in Northern and Eastern Jutland (169 farms in total) and 6 approved farms in non-approved zones. A VHS outbreak in 2001 in the approved zone: Fiskbæk Å, caused the zone status to be withdrawn from that river catchment. Countries that have implemented survey and control programmes can document their exact position with regard to freedom of certain diseases and they therefore move more intentionally towards approval than others, including re-approval after a temporary presence of a disease. The increased survey and control on a European level has had a positive impact in expanding the areas of approval and maintaining approved zones free of disease (Figure 6).
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 79
1995
2000
Figure 6. Countries participating in the survey (1995 and 2000) are marked according to approval status for VHS and IHN. Dark grey for non-approved, light grey for approved. Denmark is approved free for IHN only, and Slovenia for VHS only.
Marine VHS During the past decade, VHS has repetitively been isolated from a variety of species in the marine environment in northern Europe (Jensen et al., 1979; Jørgensen and Olesen, 1987; Dixon et al., 1997; Mortensen et al., 1999; Smail, 2000). Although the hosts seemed unaffected by the virus and the isolates were found to be low-pathogenic to rainbow trout under experimental procedures by immersion (Skall et al, in prep), these marine strains may be responsible for some of the outbreaks in marine farms cultivating susceptible species. This could be the case for the turbot farms at the Island of Gigha, UK (Ross, et al., 1994; Munro, 1996) and Cape Clear Island in Ireland (McArdle, Pers.comm. 1999) and the rainbow trout sea-farm near Göteborg in Sweden and brackish water farms in the southern Finnish Archipelago (Stone, et al., 1997; Snow et al., 1999; Einer-Jensen et al., in prep.).
List III diseases Infectious Pancreatic Necrosis (IPN) IPN emerged in the 1960ties and was regarded as a serious disease affecting rainbow trout fry and fingerlings up until 1985, where severe mortalities due to IPN were observed in Atlantic salmon post smolts (Biering, 1999). IPN is widely distributed in all major salmonid farming countries and is considered the most serious viral disease in salmon production. The disease is now endemic in most European countries and due to the horizontal and vertical transmission mode, control programmes for IPN free zones are unlikely to be approved. Sweden is the only country to claim freedom for IPNV based on a national survey. In Denmark, the disease is considered endemic like most of Europe, except for a number of approved free rainbow trout broodstock farms. Most of these farms have been maintained as closed units since 1969
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 80 and have thus been able to uphold an IPN free
ing salmon. The control policy has been partly
status and have supplied IPN free material to the international markets for decades. The
successful, and the radical poisoning approach only possible due to the special nature
future placement of IPN on list II or III is currently up for revision. An economically sig-
of the affected Norwegian streams with low species diversity and bio-mass (Mo, 1996; Mo
nificant disease, with no treatment possibility make IPN a suitable candidate for list II,
et al., 1999).
on the other hand, the lack of possibility for zoning and eradication from a defined area makes it unfit for this list.
Spring Viraemia of Carp (SVC)
The monogenean ectoparasite is primarily identified by morphology and differentiation from closely related species requires expert knowledge. G.salaris is apparently present in
The causative agent of SVC is Rhabdovirus
most Northern countries of Continental Europe without causing significant problems for
carpio (RVC) belonging to the vesiculo genus of the rhabdovirus family, also called Spring
farmed or wild fish species. G.salaris has never been encountered in the British Isles and its
Viraemia of Carp Virus (SVCV) (Fijan et al., 1971; Walker et al., 2000). SVC is distributed
introduction could have disastrous impact on the naive wild stocks of Atlantic salmon in
in all carp producing countries of continental Europe having cold winter temperatures. A
these countries. Based on national survey programmes, UK and Ireland have therefore ob-
large range of serologically related virus isolates, from carps, pikes, tench, catfish and
tained temporary additional guarantees for the introduction of salmonids (Commission
trouts are included in the disease (Vestergård Jørgensen et al.,1989). When introduced into
Decision 96/490/EC). Although G.salaris does not appear to be an important issue for
ponds or lakes it is difficult to eradicate and control. Being an OIE notifiable disease, how-
aquaculture, it will probably remain listed and likely upgraded to list II, due to the very seri-
ever, the disease will possibly be transferred from list III to list II. Only few reports of RVC
ous threat of G.salaris to the wild salmon.
isolations are recorded in the annual surveys.
Bacterial Kidney Disease (BKD) (Renibacterium salmoninarum)
Gyrodactylus salaris
BKD has been diagnosed in most salmonid
Once introduced into Norwegian rivers, presumably by infected stock from Sweden in the
producing countries in the world. The disease is difficult to treat but also difficult to control
mid 1970ties, Gyrodactylus salaris quickly became the most serious threat to native stocks
by eradication (Evelyn, 1993). Often the causative pathogen, Renibacterium salmoninarum,
of wild Atlantic salmon, eradicating whole year-classes of fish (Mo, 1996). Considerable
can be identified in populations with low and insignificant mortalities, in other cases the
efforts have been made in attempting to eradicate the parasite by rotenone treatment of
disease cause disastrous mortality (Dale, 1999). Based on a report made by the Scien-
whole river catchments, and upstream migration barriers to prevent spawning by return-
tific Veterinary Committee, BKD will probably be deleted from list III, leaving the control to
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 81 the industry. In Denmark an apparently suc-
entrance of the virus into this hatchery may
cessful control programme has been initiated in parallel with the above-mentioned IPNV
have been from wild infected fish or from either of the species Japanese flounder (hirame)
programme.
(Paralichthys olivaceus) or red seabream (Pagrus major), both of which are susceptible to the
Furunculosis (Aeromonas salmonicidae) and Enteric Redmouth Disease (ERM) These bacterial infections were both included on list III at the time when the diseases were
infection and had recently been introduced from Japan at the time (Giuseppe Bovo, Pers.comm..2001).
emerging rapidly all over Europe (Stevenson, 1993; Munro and Hastings, 1993). Today the
Iridovirosis
diseases are contained primarily by vaccination or by antibiotics (Eggset and
with extremely high mortalities in sheatfish (Siluris glanis) and catfish (Ictalurus melas),
Gudmundsdottir, 1999; Høie, 1999). Both diseases are thus about to be deleted from list
caused by systemic iridovirus infection (Ahne et al., 1989; Pozet et al., 1992; Selli and Bovo,
III. No reports of the diseases are given anymore to legal authorities in the Commu-
In prep.). The two European iridovirus isolates along with epizootic haematopoietic
nity.
necrosis virus (EHNV) from Australia are currently listed by OIE as notifiable (OIE Diag-
Potentially problematic diseases Viral Encephalopathy and Retinopathy (VER)
nostic Manual, 2000). Unfortunately there is no readily available methods for differentiat-
The last decade has seen several outbreaks
The nodavirus causing VER or Viral Nervous
ing between these three isolates and other apparently non-pathogenic strains. Although
Necrosis (VNN) is mainly a problem of saltwater-based aquaculture (OIE Diagnostic
the disease has all but devastated the existing catfish industry in northern Italy, it ap-
Manual, 2000). Although a concern in French seabass hatcheries from the early nineties
pears that clinical disease seems to be limited to warm-water culture of sheatfish and cat-
(Breuil et al., 1991) it was not until summer 1995 that a considerable number of intensive
fish in Europe.
fish farms in the Mediterranean area were affected by serious outbreaks characterised by high morbidity and mortality (Bovo et al., 2001). Over the next 5 summers, the outbreaks returned, though gradually diminishing in frequency and intensity. The most conspicuously affected species is seabass, however, many other species are susceptible. The point of origin of these outbreaks appears to be a single seabass hatchery from where young fish were transported around Europe. The
Streptococcosis The causal agent of streptococcosis is the bacteria Lactococcus garvieae. It has frequented freshwater aquaculture facilities in southern Europe for many years and is especially problematic due to its ability to develop antibiotic resistance over a relatively short period. The later years have shown a northward spreading of this pathogen into more temperate waters (Barry Hill, Pers.comm. 2000).
Bull. Eur. Ass. Fish Pathol., 22(2) 2002, 82
Epizootic Ulcerative Syndrome (EUS)
mission, together with stamping out of in-
EUS, a potentially devastating disease in freshwater finfish aquaculture, has not yet
fected farms are milestones towards the ultimate goal of eradicating a disease.
entered the European scene. This disease is responsible for substantial economic losses in
Preparation of contingency plans for diseases
Asia and is considered endemic to many areas there. The causative agent of EUS is the fungus Aphanomyces invadens, however, the aetiology of the disease is complex. A multitude of brackish and freshwater fish species are affected seasonally and due to the waterborne mode of transfer of this pathogen, eradication from natural water-bodies seem
along with prompt identification and action has prevented significant diseases from becoming established in previously naive populations. This was certainly the situation for VHS in freshwater aquaculture in USA (Håstein et al., 1999) and ISA in Scottish salmon farms (Stagg, 2001). Over the last decade new diseases have
impossible and control of the disease rather complicated (Subasinghe, 1997). With zoning,
emerged: VER, iridovirus and streptoccosis and more are likely to arrive on the arena with
health certificates and quarantine, EU has a proficient system in place to protect its
time. However, with the awareness in the Community, the existing quarantine and sur-
aquaculture from alien pathogens. With respect to EUS it may rather be a matter of in-
vey system together with the accumulated experience in fish disease circles, EU stands a
compatible environmental conditions, than a waterproof quarantine service. In time, European fish pathologists may get a chance to
reasonable chance of an early detection followed by a concerted action to contain and
diagnose EUS, and its point of entry could well be via the less monitored trade of orna-
control a new disease providing the necessary contingency plans are in place for the different diseases in the respective countries.
mental fish.
Summary
Acknowledgements: A big ‘Thank You’ to all our colleagues in
Despite disease obstacles, aquaculture in Europe has undergone an expansion, both in
National Reference Laboratories for Fish Diseases who struggled with numbers and dead-
terms of new species and production volume. Diseases that previously were of major nui-
lines year after year, and helped uncover old files for the purpose of completing this publi-
sance to the industry are in many cases contained or controlled through means of thor-
cation.
ough understanding of transmission and host susceptibility. Implementation of suitable pro-
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