Following diagnostic testing of a sample of fish from the affected fishery, the FHI placed an initial designation (ID) on the site after a presumptive positive test for spring viraemia of carp (SVC).
Following genetic sequencing and phylogenetic analysis, the virus isolated from the common carp sampled from Crockwell Farm Lakes was confirmed as SVC virus of genotype 1d. This strain of SVC is considered to be of European origin.
This is the first isolation of this genotype from an SVC outbreak in GB since 1997, (and the first outbreak of SVC in a fishery since 2007). Genotype 1d was implicated in the largest SVC outbreak that occurred in GB in 1988 when around 44 waters were infected. That outbreak was directly linked to an illegal import of fish from continental Europe.
Following a thorough investigation, there was no evidence of any illegal introductions of fish to the lakes at Crockwell Farm Fishery. However, an epidemiological study of the disease outbreak concluded that live fish movements were the most likely source of infection and it remains a possibility that unauthorised fish introductions were made without the knowledge or consent of the fishery owner.
Cefas, acting on behalf of Defra, issued a confirmed designation (CD 02/2011) on 13 June 2011 prohibiting the movement of fish to, from and within Crockwell Farm Fishery. The CD also restricts movement of equipment onto and from the site. The fishery will remain closed until the disease issue is resolved.
Fish Health Inspectors have now begun the process of clearance and disinfection to prevent the spread of the disease which is considered to be exotic to the United Kingdom following a successful eradication programme which started in 2004 and was completed in 2010.
The FHI and local EA Fisheries teams have initially removed over a tonne of mixed coarse fish from the water (predominantly carp, tench and roach) using a combination of seine netting and electro-fishing. The purpose of this exercise was to remove as many of the moribund and potentially infectious animals as possible to prevent any wider spread of the disease by mammalian or avian predators. The fish were humanely culled and incinerated as required under legislation on the safe disposal of animal wastes.
The lakes, which cover an area of approximately 1.75 acres, will be drained to nearby arable land and the remaining stocks will be culled as the water level drops. The silt will then be removed using assorted plant machinery, and disinfected using quick lime in line with FHI procedures.
This outbreak of SVC illustrates the need for fishery managers, fish farmers and others involved in the husbandry of live fish to:
- ensure that effective biosecurity measures are in place to reduce the risk of disease incursions, and
- remain vigilant over the physical security of their sites so that the unauthorized removal or introduction of fish cannot take place.
Further information on biosecurity and protecting your fish stocks is available on www.defra. gov.uk/aahm/forms/guidelines-list/.
SVC affects a wide range of fish including all species of carp, goldfish, tench, orfe and Wels catfish and can result in high mortality rates.
It is widespread in continental Europe and western Eurasia. Outbreaks of SVC usually occur as water temperatures rise above 7°C in the Spring. Maximum mortalities typically occur between 10° and 15°C, usually ceasing above 17°C. However, SVC is not restricted to the Spring and a number of significant mortality events have occurred in the Autumn as water temperatures fall.
Clinical signs of SVC can vary but usually include darkening of the skin, lethargy, swollen eyes, abdominal swelling (dropsy), pale gills and training faecal casts. SVC is normally spread through close contact with infected fish. Some parasite vectors, such as fish lice (Argulus) and leeches (Piscicola), can also transfer the disease from infected to healthy fish. There are no treatments for SVC.
In the event of a suspected or confirmed outbreak in the UK, the FHI will place immediate restrictions on the affected water preventing any movements into, out of and within the site. We will then seek to cull the affected stocks and disinfect the site wherever possible. Movement controls will only be lifted after this process has been completed.
As with any notifiable fish disease in the UK, there is a legal obligation to report any suspicion of a clinical outbreak of SVC to the Fish Health Inspectorate on 01305 206700. Fishery owners and managers must be sure that any fish introduced to their waters are free of disease. Never buy any fish of unknown provenance. One “bargain” fish may cost the stock and reputation of the fishery.