Acta vet. scand. 2001, Suppl. 94, 43-50.

Surveillance of Fish Diseases in the Nordic Countries

By T. Håstein1, A. Hellstrøm2, G. Jonsson3, N. J. Olesen4, E. R.-Pärnänen5

1National Veterinary Institute, P.O.Box 8156 DEP, 0033 Oslo, Norway, 2National Veterinary Institute, P.O.Box 7073, SE-75007 Uppsala, Sweden, 3Veterinary Officer for Fish Diseases, Keldur, Vesturlandsveg, IS-112, Reyk- javik, Iceland, 4Danish Veterinary Laboratory, Aarhus, Denmark, 5National Veterinary and Food Research Insti- tute (EELA), P. O. Box 368, Fin-00231 Helsinki, Finland.

Due to the increasing importance of disease problems in the fish farming industry and the impact disease may have on both feral and farmed fish in the Nordic countries, mon- itoring and surveillance on diseases have for many years been considered to be of socio- economic importance. All the Nordic countries have a national legislation as basis for their surveillance and disease control in aquatic and regulations listing notifi- able diseases of concern to the countries. The list of diseases vary between the countries. In addition, Denmark, Finland and Sweden are ruled by Directive 91/67/EEC as regards placing on the market of aquaculture animals and products. The surveillance for viral diseases in all the Nordic countries has mainly been based on the testing procedures given in the EU Commission Decision 96/240/EC.

The list of diseases to be monitored or surveyed salaris for wild stocks of Atlantic for varies between the Nordic countries. All the , a surveillance programme for this par- Nordic countries run a surveillance programme asite is under consideration in Norway, while in for Viral Haemorrhagic Septicaemia (VHS) Finland regular monitoring for the parasite and Infectious Haematopoietic Necrosis (IHN) takes place in certain regions recognised to be based on EU regulations and a monitoring pro- free of the parasite in order to obtain additional gramme for Infectious Pancreatic Necrosis guarantees within the EU. Similarly, (IPN) on a national level. Iceland and Norway Finland, Iceland and Sweden run a national have also established a surveillance programme control programme for furunculosis for the for Viral Nervous Necrosis (VNN) on a na- same reason and Finland has asked for addi- tional level, while Finland and Sweden has es- tional guarantees for certain areas in which the tablished a surveillance programme for Spring disease do not occur. Viraemia of carp (SVC) on a national level in The measures taken when disease occur vary order to obtain additional guarantees within the from restrictions on movements to stamping out EU for that disease. Norway is the only country procedures as well as disinfection procedures that has established a control programme for and other means to establish control of a dis- Herpesvirus scophthalmi in turbot, for Anguil- ease. The ultimate goal is to eradicate or keep licola spp in eel and for pasteurellosis in sea the level of disease to a minimum. bass. These programmes are due to start year 2000. Monitoring of Bacterial Kidney Disease Introduction (BKD) takes place in all the Nordic countries; On a global scale, fish and fishery products are in some of the countries it is being compulsory the main food supply for human beings and and in others it is carried out on a voluntary ba- these products constitutes more than 80% of the sis. Due to the importance of the haptorworm total amount of seafood consumed. It is widely

Acta vet. scand. Suppl. 94 - 2001 44 known that the supplies of fish from traditional several different marine species such as halibut fisheries are more or less constant (FAO Aqua- (Hippoglossus hippoglossus), turbot (Scoph- culture Statistics) and that the shortage in fish thalmus maximus) and sea bass (Dicentrarchus and fish products has to be met by aquaculture. labrax) have gained increased importance. The potential for the aquaculture industry to Table 1 gives an overview over the fish species meet the challenge as regards food security has farmed in the Nordic countries as well as the been clearly demonstrated by the rapid expan- size and production of these species. sion of the fish farming industry world wide (Roberts & Muir, 1995). Fig. 1 shows the de- The rational for disease surveillance velopment of aquaculture compared to global Over the last decades, several emerging or seri- fisheries in the period 1987-1997 (FAO). The ous diseases in fish have been diagnosed in figures show that the total capture in fisheries is farmed and feral populations, creating large relatively constant at some 90 millions metric problems in the fish farming industry and thus tonnes while there has been an increase in aqua- being the subject of surveillance and monitor- culture production from 10 millions metric ing programmes in many countries (Håstein, tonnes to 28 millions metric tonnes in the same 1995). The differences between infectious dis- period. eases in fish and those of terrestrial animals The way fish farming is conducted and the means that the approach to the problems and species farmed vary considerably in the world the eradication efforts differ as the diseases may depending on geographical conditions, water spread effectively through flowing water resources, temperature etc. (Håstein, Hill & Winton, 1999). Following is the described basis for and the re- Fish farming in the Nordic countries sults of monitoring and surveillance pro- In the Nordic countries, the fish farming indus- grammes as well as established measures on try is mainly based on salmonid species, At- some of the diseases considered to be of major lantic salmon ( salar) and concern in the Nordic countries. ( mykiss), but in the later years

Fig. 1. Aquaculture and global fisheries production (FAO information).

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Table 1. Fish farming in the Nordic countries; No. of farms, species and production

Total production Species kept under farming Country No. of farms all species conditions Metric tons

Denmark 478 Eel, Rainbow trout 46.000

Finland 333 Arctic char, Baltic salmon rainbow trout, whitefish 16.597

Iceland 40 , Arctic char, rainbow trout, halibut, Sea bass 3.669

Norway 1169 Atlantic salmon, Arctic char, brown 390.764 (salmonids) trout, Cod, eel, halibut, turbot, sea bass 381 (others)

Sweden 177 Arctic char, Baltic salmon, 6.200 rainbow trout, grass carp

Basis for the monitoring and surveillance in tries. All the countries runs a surveillance pro- the Nordic countries gramme for Viral Haemorrhagic Septicaemia All the Nordic countries have a national legisla- (VHS) and Infectious Haematopoietic Necro- tion as basis for their surveillance and disease sis (IHN) based on EU regulations (Ariel, Hel- control in aquatic animals, as well as regula- gason, Mortensen & Olesen,1999) and a moni- tions listing notifiable diseases of concern to toring programme for Infectious Pancreatic the countries. The list of notifiable diseases Necrosis (IPN) on a national level. The Nordic vary from country to country. In addition to countries have also a clinical monitoring for in- their national legislation, Denmark, Finland fectious salmon anaemia (ISA) as no validi- and Sweden are ruled by Directive 91/67/EEC dated surveillance methods so far have been es- as regards placing on the market of aquaculture tablished. Iceland and Norway has also animals and products, but even Iceland and established a surveillance programme for Viral Norway have accepted the principles laid down Nervous Necrosis (VNN) on a national level, in the Directive. while Finland and Sweden have established a The monitoring and surveillance for viral dis- surveillance programme for Spring Viraemia in eases in all the Nordic countries has mainly carp (SVC) on a national level in order to obtain been based on the testing procedures given in additional guarantees within the EU for that the EU Commission Decision 96/240/EC while disease. Norway is the only country that have for the bacterial and parasitic diseases, standard established a control programme for Herpes- diagnostic procedures for such diseases has virus scophthalmi in turbot, for Anguillicola been used for screening purposes. spp in eel and for pasteurellosis in sea bass The list of diseases under monitoring and which will start year 2000. surveillance varies between the Nordic coun- Monitoring for Bacterial Kidney Disease

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Table 2. Diseases and target species under surveillance in the Nordic countries

Disease Target species Country

Viral Diseases Infectious salmon anaemia (ISA) Salmonids Denmark, Finland, Iceland, Norway, Sweden Infectious pancreatic necrosis (IPN) Salmonids Denmark, Finland, Iceland, Norway, Sweden Infectious haematopoietic necrosis (IHN) Salmonids Denmark, Finland, Iceland, Norway, Sweden Viral haemorrhagic septicaemia (VHS) Salmonids Denmark, Finland, Iceland, Norway, Sweden Spring viremia in Carp (SVC) Carp Finland, Sweden Viral nervous necrosis (VNN) Halibut Iceland, Norway, Herpesvirus scophthalmi infection Turbot Norway

Bacterial diseases Bacterial kidney disease (BKD) Salmonids Denmark, Finland, Iceland, Norway, Sweden Furunculosis Salmonids Finland, Iceland, Sweden Pasteurellosis Sea bass Norway

Parasitic diseases Gyrodactylus salaris Salmonids Finland, Norway Anguillicola spp Eel Norway

(BKD) takes place in all the Nordic countries; may be present on a low level such as IPN in in some of the countries being compulsory and Finland and Sweden, the ultimate aim will in others carried out on a voluntary level. probably be eradication. Due to the importance of the haptorworm Gy- rodactylus salaris for wild stocks of Atlantic Surveillance programmes and target salmon, a surveillance programme for this par- populations asite is under consideration in Norway, while in The main target population for the monitoring Finland regular monitoring for the parasite and surveillance programmes is salmonids for takes place in certain regions recognised to be most of the diseases under surveillance. free of the parasite to obtain additional guaran- The size of the target populations is given in tees within the EU. Similarly Finland, Iceland Table 1. All types of farms are included in the and Sweden runs a national control programme survey such as hatcheries, brood stock farms as as regards furunculosis for the same reason and well as grow out farms, table 2 shows the dis- Finland has asked for additional guarantees for eases under surveillance and the target species certain areas in which the disease due not occur. for the disease in question. Denmark, Norway and Scotland run a surveil- Aim of surveillance lance programme with the aim of deriving in- The aim of the monitoring and surveillance formation on VHS virus and other viral infec- programmes for fish diseases in question in the tions in wild marine populations is carried out Nordic countries is either to document and in European coastal waters from the English maintain freedom of disease, to eradicate a dis- channel in the south to the Spitsbergen area as ease or to keep a disease under control within well as in the Baltic sea (Mortensen, Heuer, certain bonds. For some of the diseases that Lorenzen, Otte, Olesen, 1999, Olesen, 1997).

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Similar examinations were carried out by Swe- nary Officer for Fish Diseases. den in the Baltic sea and Kattegat in 1998 and In Denmark, the Danish Veterinary and Food the beginning of 1999. Administration do the necessary sampling and control. Organisation Analyses of the diseases under surveillance are The basis for the different surveillance and carried out at official veterinary laboratories i.e. monitoring programmes in formal terms is National Veterinary Institute in Norway and partly based on EU regulations, OIE criteria or Sweden, the Veterinary Officer for Fish Dis- criteria derived from national legislation. For eases, Keldur, in Iceland, Danish Veterinary some of the diseases such as IHN and VHS, the Laboratory in Denmark and National Veteri- participation is compulsory in all the Nordic nary and Food Research Institute (EELA) in countries as regards approval and maintenance Finland. of disease free status for the two diseases either for the whole country, for zones or for farms in Test and testing procedures non approved zones. In Denmark a control pro- The surveillance for viral diseases in all the gram for VHS started as early as in 1965, while Nordic countries has mainly been based on the in Finland, Iceland, Norway and Sweden an of- testing procedures given in the EU Commission ficial surveillance program started in 1995, Decision 96/240/EC. According to the deci- 1993, 1994 and 1993 respectively. For other sion, fish farms are inspected clinically biannu- diseases such as furunculosis the participation ally and samples for virological examinations is compulsory in some countries such as Swe- are collected by rotation in 50% of the fish den, while it is voluntary or even non existing farms each year to document freedom for IHN on a regular basis in other countries such as and VHS. In Denmark, Finland, Iceland and Norway. Sweden, all or some of the same samples are In Finland, the surveillance programme for G. used for IPN testing. In Denmark, the control of salaris has been compulsory for the last three IPN is based on the monitoring of IPN free years. broodstock farms and ongrowing farms as IPN is considered to be endemic in non controlled Sampling farms. In Norway testing for IPN virus is done The sampling of fish for surveillance vary be- in a specific monitoring programme in brood tween the Nordic countries depending on the stocks of Atlantic salmon and rainbow trout as infrastructure of the health control in the differ- IPN virus neutralisation is used in the examina- ent countries. In Sweden the National Fish tions for IHN/VHS virus. Health Service (Fiskhälsan FH AB) are respon- The examination procedures given in the OIE sible for all sampling, while in Norway, the re- Diagnostic Manual for Aquatic Dis- sponsible Authorithy is the district veterinary eases are the basis for examinations as regards officers (DVO) or local fish health services op- BKD, Gyrodactylus salaris and VNN while for erating under instruction of the DVO. In Fin- furunculosis, pasteurellosis and Anguillicola land the municipal veterinarians do the neces- spp, standard bacteriological or parasitological sary sampling when inspecting the farms which procedures are used, respectively. The fre- is done biannually. quency in the testing of these diseases is vary- In Iceland, the responsible authority as regards ing between the countries. sampling is under the supervision of the Veteri-

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Measures taken when positive diagnosis disease is considered to be enzootic. In Norway, occur restrictions are laid upon farms if the furuncu- In all the Nordic countries, it is the Veterinary losis is diagnosed. Hatcheries are not allowed to Authorities that is responsible for the imple- sell live fish while affected fish farms in sea wa- mentation of measures that will be used in or- ter may keep the fish until reaching marketable der to control a given notifiable disease. The size for slaughtering. implementation involves both central and re- In all the Nordic countries an infected farm gional veterinary officers. may restock after fallowing if no signs of in- In all the Nordic countries except non-approved fection appear after a sanitation programme has zones in Denmark, stamping out procedures been carried out. followed by cleaning, disinfection and fallow- ing will be carried out if VHS is diagnosed Economic compensation (Olesen, Korsholm, 1997, Olesen, 1998). In In Sweden, all expenses will be paid by the non-approved zones in Denmark, a stamping Board of Agriculture for IHN, VHS, SVC and out program will be started if 1/3 of the farms IPN as these diseases are included in the epi- in a river system agrees to an eradication pro- zootic act. Similarly, in Finland, the govern- gram to get rid of the disease. ment will pay for all expenses if IHN and VHS Since IHN and SVC is considered to be absent are detected, probably also for SVC. In Norway in all the Nordic countries, stamping out proce- affected farm(s) will have to pay themselves for dures will be applied to these diseases. As re- any measures imposed by the authorities for the gards IPN, the detection of the disease or the time being, because no compensation is virus as such, will be subject to restrictions fol- granted. lowed by a sanitation programme laid down by In Denmark expenses will probably be paid in the Board of Agriculture in Sweden, while in case of IHN and ISA outbreaks and in case of a Norway the mere detection of IPN virus will VHS outbreak in approved zones free of VHS, not bring about any restrictions. Clinical IPN expenses might be covered as well. will, however, lead to restrictions on movement of live fish in Norway as long as mortality and Certification signs of the disease occur. In Finland, isolation Health certificates and/or transportation docu- of IPN virus will lead to restrictions on move- ments is needed in connection with deliveries ment of live fish in continental zones, while of live fish for stocking into grow out farms and clinical IPN probably will result in more strong restocking into rivers. Additionally, in Norway measures. These have so far not been deter- it is not allowed to move fish prior to slaughter, mined. Prevention may be achieved by avoiding when they are stocked in a sea water site. This introduction of disease free eggs and/or fish is to prevent spread of disease if disease occur. into disease free farms as well as using pro- tected water supply (e.g. spring-, borehole wa- Record keeping ter). In all the Nordic countries, the record of find- In Iceland, detection of furunculosis is also fol- ings are kept by the responsible authorities, lowed by stamping out because the disease is both regionally and centrally. The diagnostic recognised as a List A disease, while in Sweden laboratories also keep the necessary documen- active measures are taken only if the disease oc- tation on the examinations carried out. Further- cur in freshwater, but not in sea water where the more all farms have to keep records on events in

Acta vet. scand. Suppl. 94 - 2001 49 the farms that can be requested by Competent farms/hatcheries since its first detection. Responsible Authorithy. Anguillicola crassus has so far been reported from Denmark, Norway and Sweden, but the Current status distribution in the wild is not known. While still a few cases of VHS is diagnosed in Denmark each year, Finland, Iceland, Norway Conclusion and Sweden are considered to be free from Although some differences occur, all the VHS. However, VHS was diagnosed in one Nordic countries have established appropriate farm in Norway and Sweden in 1998. All surveillance and monitoring for fish diseases of Nordic countries have status as free from IHN concern to the fish farming industry. Due to and SVC although only Finland and Sweden is these systems and good management practises, carrying out a specific surveillance programme the fish disease situation in the Nordic countries for SVC. is generally good compared to other countries IPN is considered to be the main viral disease in the world. problem in Norway. The disease is endemic in Denmark but not considered as a mayor prob- References lem. The disease level of IPN is low in Finland Ariel E, Helgason S, Mortensen HF, Olesen NJ and Sweden and so far not reported in Iceland. (1999). Report of the Third annual Meeting of EU National Reference Laboratories for Fish Iceland is considered to be free from classical Diseases, Aarhus, Denmark 9.th-11th June 1999. furunculosis, while the disease appears to be 31 pp. endemic in Denmark, Finland, Norway and Decision 96/240/EC: Laying down the sampling Sweden. However, some areas in Finland are re- plans and diagnostic methods for the detection ported free of furunculosis and the authorities and confirmation of certain fish diseases. Directive 91/67/EEC: Placing on the market of aqua- has established so-called protective zones to culture animals and products. which live fish and fish eggs only can be trans- FAO Aquaculture production and statistics 1988- ported if special permission is granted. 1997, Information, Data and Statistics BKD has been reported from all the Nordic Unit, FAO Department, 203pp. Heuer OE, Lorenzen E, Korsholm H, Hansen RG, countries but the level appear to be relatively Olesen NJ (1999). BKD i Danmark: Status efter low (Heuer, Lorenzen, Korsholm, Hansen, Ole- to sæsoner. Ferskvandsfiskeribladet, 97, 5, p 116- sen, 1999, Lorenzen, Korsholm, Olesen, Heuer, 118. 1997). In Iceland. the disease has occasionally Håstein T. (1995). Disease problems, use of drugs, been detected in wild Atlantic salmon returning resistance problems and preventive measures in fish farming world wide. In Sustainable Fish to spawning grounds while it has not been de- Farming, eds. Reinertsen H & Haaland H., 183- tected in farms for the last 4 years. BKD was for 194. the first time detected in wild salmon in the Håstein T, Hill BJ, Winton JR (1999). Succesful Baltic sea in 1999, so it is quite apparent that a aquatic animal disease emergency programmes. reservoir of the disease exists in the wild. Rev. sci. tech. Off. int. Epiz., 18 (1), 214-227. Lorenzen E, Korsholm H, Olesen NJ, Heuer OE Gyrodactylus salaris has been described from (1997). Påvisning af bakteriel nyresyge (BKD) Denmark, Finland, Norway and Sweden, but it hos regnbueørred i Danmark. Ferskvandsfiskeri- is only in Norway that disease caused by this bladet, 95, 7, p 160-168. parasite has given high mortality in feral fish Mortensen HF, Heuer OE, Lorenzen N, Otte L, Ole- sen NJ (1999). Isolation of Viral Haemorrhagic populations in Norway. The parasite has now Septicaemia Virus (VHSV) from Wild Marine totally been detected in 40 rivers and 37 Fish Species in the Baltic Sea, Kattegat, Skager-

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rak and the North Sea. Virus Research, 63, 95- Olesen NJ (1998). Sanitation of Viral Haemorrhagic 106. Septicaemia (VHS). J. Appl. Ichthyol. 14, 173- OIE Diagnostic Manual for Aquatic Animal Diseases 177. (1997), 251pp. Roberts RJ, Muir JF (1995). 25 years of world aqua- Olesen NJ, Korsholm H (1997). Control measures for culture: Sustainability, a global problem. In Sus- viral diseases in aquaculture: Eradication of VHS tainable Fish Farming, eds. Reinertsen H & Haa- and IHN. Bull. Eur. Ass. Fish Pathol.17, 229-233. land H., 167-181 . Olesen NJ (1997). Isolering og karakterisering af VHS virus fra saltvandsfisk . Ferskvandsfiskeri- bladet, 95, 6, p 129-130.

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