Fisheries Research Services

Fisheries Research Services is an agency of the Scottish Executive

FRS Marine Laboratory PO Box 101 375 Victoria Road Aberdeen AB11 9DB UK

tel +44 (0)1224 876544 fax +44 (0)1224 295511

enquiries@marlab.ac.uk http://www.frs-scotland.gov.uk

Viral Haemorrhagic Septicaemia (VHS) andInfectious Haematopoietic Necrosis (IHN)VHS and IHN are List II diseases. Due to their limiteddistribution, distinct geographical zones may be declaredfree of these diseases. The whole of Great Britain is adisease free zone with regard to VHS and IHN. Imports oflive fish from zones or farms of lower health status areprohibited. Signs of VHS and IHN include swollenabdomen, ‘pop eye’ and haemorrhaging of the internalorgans and body wall (Fig. 2).

Infectious Salmon Anaemia (ISA)ISA is a List I disease. The measures described in theDiseases of Fish (Control) Regulations 1994, which imposeEU Directive 93/53/EEC, were implemented when anoutbreak of ISA occurred in Scotland in 1998. The diseasewas inadvertently spread by movements of live fish andcontact between fish farms. Currently, there are no suspector confirmed infected farms in Scotland. Signs of ISAinclude pale gills and a dark liver (Fig. 1).

Notifiable Diseases in Fish

IntroductionLegislation to prevent the introduction and spread ofserious disease in fish was introduced in the UK as earlyas 1937 in the form of the Diseases of Fish Act 1937(DoFA). This was necessary because of the devastatingeffect of furunculosis on wild salmon stocks. The DoFAintroduced the legal requirement to notify the Minister ofthe suspicion of the presence of certain diseases in fish.Such diseases are referred to as Notifiable Diseases. InScotland, Fisheries Research Services (FRS) acts on behalfof the Scottish Ministers in this respect.

Restrictions on the import into the UK of live fish haveplayed a major part in preventing the introduction andspread of serious fish diseases. EU Council Directive91/67/EEC defines the animal health conditions governingthe placing on the market of aquaculture animals andproducts. The Directive categorises diseases as List I,List II or List III. List I diseases are exotic to the EU anderadication measures are mandatory where a List I diseaseis detected. List II diseases have limited distribution inthe EU. There are controls on trade between infected andnon-infected areas. List III diseases are relativelywidespread, and Member States may apply for approvalfor a national control programme for these diseases.

Great Britain has an approved control and eradicationprogramme for bacterial kidney disease (BKD), springviraemia of carp (SVC) and Gyrodactylus salaris, andadditional guarantees on imports of live fish are grantedunder Commission Decision 2004/453/EC. This enablesthe restriction of imports to zones or farms of equal orhigher health status. Figure 2. Post mortem findings associated with VHS

Figure 1. Post mortem findings associated with ISA

Inspection of fish farms

Fisheries Research Services

Fisheries Research Services is an agency of the Scottish Executive

FRS Marine Laboratory PO Box 101 375 Victoria Road Aberdeen AB11 9DB UK

tel +44 (0)1224 876544 fax +44 (0)1224 295511

enquiries@marlab.ac.uk http://www.frs-scotland.gov.uk

Spring Viraemia of Carp (SVC)SVC is a List III disease caused by a rhabdovirus which isclosely related to the viruses which cause VHS and IHN.It affects certain carp species and other cyprinid fish suchas goldfish, roach, tench and pike. SVC is rarely found inScotland. Signs include swollen abdomen and bleedingin the gills and skin.

GyrodactylosisGyrodactylosis is a List III disease caused by Gyrodactylussalaris, a monogenean helminth parasite. It has neverbeen detected in the UK, but has resulted in widespreadloss of salmon stocks in some Norwegian rivers. Theparasite reproduces very quickly and causes death insusceptible species due to damage to the skin.

Control of DiseaseIn the event that a Notifiable Disease is suspected orconfirmed in a population of fish on a farm, a Thirty DayNotice (TDN) is served. A TDN temporarily restricts themovement of live fish, eggs or gametes to or from thefarm. Samples are taken by the Fish Health Inspectoratefor laboratory analysis to confirm or rule out the presenceof disease. A second TDN may be issued where the diseaseis still suspected but confirmation has not been possiblewithin 30 days, or where no action has been taken tofallow the farm.

Bacterial Kidney Disease (BKD)BKD is a List III disease caused by the bacterial agentRenibacterium salmoninarum. BKD primarily affects troutand salmon, although the bacterium has been isolatedfrom other fish species. The disease is characterised byan enlarged, granular kidney and spleen and there maybe white lesions in the kidney and other internal organs(Fig. 3). Currently, less than 5% of farms in Scotland areinfected with BKD.

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Where a farm is confirmed infected, or where the suspicionof infection cannot be ruled out within 60 days, aDesignated Area Order (DAO) is made. A DAO can only berevoked by making a DAO Revocation Order. A DAO canbe revoked when the infected farm has been cleared ofall stock and disinfected according to the standarddisinfection procedures* (a fallow period may be required),or where steps have been taken to remove the infectedstock and a programme of sampling has proved negativeover a specified time period (these programmes varydepending on the disease).

Surveillance and MonitoringThe FRS Fish Health Inspectorate conducts veterinarysurveillance for Notifiable Diseases of fish in Scotland.To maintain disease free status for VHS and IHN and theadditional guarantees for BKD, SVC and gyrodactylosis,every fish farm holding susceptible species is inspectedat least once a year by the Fish Health Inspectorate. Asample of 30 fish is taken from each farm at least everysecond year (Fig. 4). In addition, all freshwater farmsholding salmonids are sampled every second year forGyrodactylus salaris.

*Current disinfection guide available from the Librarian at the address below.

Figure 3. BKD lesions

Figure 4. Sampling

Who to ContactIf you suspect the presence of a Notifiable Disease, ifunexplained mortalities occur at your fish farm, or if yourequire more information, contact the fish healthinspectorate at the address below:

Tel: 01224 295525Fax: 01224 295620Email: FishHealth@marlab.ac.uk

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