• Management and control of proliferative kidney disease (PKD) in a freshwater Atlantic salmon (Salmo salar L.) farm in Ireland: a case history

      Quigley, D.T.G.; McArdle, J.F. (Fish Veterinary Society, 1998)
      During July 1992, an acute clinical outbreak of proliferative kidney disease (PKD) was experienced in two strains (‘Irish’ and ‘Norwegian’) of juvenile (age 0+) Atlantic salmon (Salmo salar L.) held at two adjacent freshwater sites on the River Lee in southern Ireland. Various management strategies (including reduced stocking densities, handling, feeding rates and increased oxygenation), and treatment regimes (involving malachite green and fumagillin DCH) were used to control the disease. A total of 1·3 million juveniles died during the PKD outbreak, representing 61·6% and 54·6% of the Norwegian stock at the two farms respectively. The Irish stock appeared to be more resistant to the disease and only 15·6% died. The weekly prevalence of PKD fluctuated throughout the summer but seemed to disappear by mid-August. Although PKD was detected again during 1993, no clinical outbreak occurred. In conjunction with the management strategies adopted in 1992, seven consecutive weekly prophylactic bath treatments with malachite green (1·6 ppm for 40 minutes) administered prior to mid-July appeared to control the disease. During August 1993, a ten day course of fumagillin (6 mg/kg bodyweight per day) reduced the prevalence of the PKD parasite in a trial batch of juveniles from 24% to zero. The results of this study demonstrated the effectiveness of various management strategies and treatment regimes in controlling PKD.
    • Modelling origin and spread of Infectious Pancreatic Necrosis Virus in the Irish salmon farming industry: the role of inputs

      Ruane, N.M.; Murray, A.G.; Geoghegan, F.; Raynard, R.S. (Elsevier, 2009)
      Observed emergence of IPNV in farmed Irish salmon is simulated using a model originally developed to analyse the spread of the virus in Scotland [Murray, A.G., 2006a. A model of the spread of infectious pancreatic necrosis virus in Scottish salmon farms 1996–2003. Ecol. Model. 199, 64–72]. IPNV appears to have become established relatively recently in Ireland and the model is altered to explicitly simulate the origin of the spread of the virus. Input to freshwater farms was key to initiation of infection, but modelling suggests that endogenous spread was responsible for much of the subsequent increase in prevalence of IPNV. From the modelling, it is unlikely that direct imports accounted for most IPNV cases. If this is the case, cessation of imports, without a substantial improvement in biosecurity, would be likely to be of only limited effect in controlling IPNV. Marine IPNV prevalence appears to be insensitive to direct interventions in the marine environment (as in the Scottish model). A multi-element control strategy, targeting both endogenous spread and external input of infection and prioritising freshwater sites, but extending to marine sites, would probably now be required to eradicate IPNV from Ireland.
    • Molecular differentiation of infectious pancreatic necrosis virus isolates from farmed and wild salmonids in Ireland

      McCarthy, L; Swords, D; Ruane, N. M. (Wiley-Blackwell, 2009)
      This study investigated the genotypes and sub-groups of infectious pancreatic necrosis virus (IPNV) present in farmed and wild salmonid fish in Ireland. An 1100-bp portion of the VP2 region of segment A from each of 55 IPNV isolates collected over 2003–2007 was amplified by reverse-transcription–polymerase chain reaction and the product directly sequenced. The nucleotide sequences of each isolate were aligned and compared with each other and with the corresponding sequences of a number of reference isolates. All the 55 sequenced isolates belonged to genogroup 5 (Sp serotype) and could be divided into two subgroups. Irish subgroup 1 consisted of isolates from farmed salmon originating from an Irish salmon broodstock. Irish subgroup 2 consisted of isolates from imported farmed stock and all reported clinical outbreaks of IPN were associated with isolates from subgroup 2. Isolates from wild fish were identical to some isolates from subgroup 2, and therefore are believed to have originated from infected farms. These results highlight the importance of import risk analysis for diseases not listed under current legislation.
    • An outbreak of francisellosis in wild-caught Celtic Sea Atlantic cod, Gadus morhua L., juveniles reared in captivity

      Ruane, N.M.; Bolton-Warberg, M.; Rodger, H.D.; Colquhoun, D.J.; Geary, M.; McCleary, S.J.; O´Halloran, K.; Maher, K.; O´Keeffe, D.; Mirimin, L.; et al. (Wiley, 2013)
    • Phylogenetic analysis of infectious pancreatic necrosis virus in Ireland reveals the spread of a virulent genogroup 5 subtype previously associated with imports

      Ruane, N.M.; McCleary, S.J.; McCarthy, L.J.; Henshilwood, K. (Springer Verlag, 2015)
      Infectious pancreatic necrosis is a significant disease of farmed salmonids resulting in direct economic losses due to high mortality and disease-management costs. Significant outbreaks of the disease occurred in farmed Atlantic salmon in Ireland between 2003 and 2007, associated with imported ova and smolts. As the virus was known to occur in the country since the development of aquaculture in the 1980s, this study examined archived samples to determine whether these older isolates were associated with virulent forms. The study showed that two genotypes of IPNV were present in the 1990s, genotype 3 and genotype 5. A more virulent subtype of the virus first appeared in 2003 associated with clinical outbreaks of IPN, and this subtype is now the most prevalent form of IPNV found in the country. The data also indicated that IPNV in Ireland is more closely related to Scottish and continental European isolates than to Norwegian, Chilean and Australasian genogroup 5 isolates.
    • Reproductive Failure of Landlocked Atlantic Salmon from New York's Finger Lakes: Investigations into the Etiology and Epidemiology of the “Cayuga Syndrome”

      Fisher, J.P.; Spitsbergen, J.M.; Rodman, G.; symula, j. (American Fisheries Society, 1995)
      We describe a disease syndrome that afflicts larval, landlocked Atlantic salmon Salmo salar from Cayuga Lake, one of central New York's Finger Lakes. Mortality associated with the “Cayuga syndrome” is 98–100%. Death usually occurs between 650 and 850 centigrade degreedays after fertilization, approximately 2–4 weeks before yolk resorption is complete. Although there is minor temporal variation in the onset of the Cayuga syndrome in progeny from individual females, all sac fry eventually succumb. Incubation of embryos and sac fry under constant, ambient, or reduced temperature regimens slightly alters the degree-day timing of syndrome onset, but does not improve survival. Based on mortality rate, manifestation of the Cayuga syndrome has not changed in the past 10 years, even though incubation waters of varying chemistry and temperature have been used. Mortality of the negative control stocks used for these studies never exceeded 10% from hatching to first feeding. Findings from reciprocal crossbreeding experiments indicate the problem is associated with ova only. A noninfectious etiology is indicated by the lack of consistently identifiable fish pathogens from syndrome-afflicted sac fry and by the failure to transmit the condition horizontally. Suspect contaminants were eliminated as potential causative factors. Epidemiological studies on the viability of other Finger Lakes stocks indicate that Atlantic salmon from Keuka and Seneca lakes are also afflicted (100% mortality). yet those from Skaneateles Lake are not. The cause of this syndrome appears to be nutritional.
    • Risk factors associated with increased mortality of farmed Pacific oysters in Ireland during 2011

      Clegg, T.A.; Morrissey, T.; Geoghegan, F.; Martin, S.W.; Lyons, K.; Ashe, S.; More, S.J. (Elsevier, 2014)
      The Pacific oyster, Crassostrea gigas, plays a significant role in the aquaculture industry in Ireland. Episodes of increased mortality in C. gigas have been described in many countries, and in Ireland since 2008. The cause of mortality events in C. gigas spat and larvae is suspected to be multifactorial, with ostreid herpesvirus 1 (OsHV-1, in particular OsHV-1 μvar) considered a necessary, but not sufficient, cause. The objectives of the current study were to describe mortality events that occurred in C. gigas in Ireland during the summer of 2011 and to identify any associated environmental, husbandry and oyster endogenous factors. A prospective cohort study was conducted during 2010–2012, involving 80 study batches, located at 24 sites within 17 bays. All 17 bays had previously tested positive for OsHV-1 μvar. All study farmers were initially surveyed to gather relevant data on each study batch, which was then tracked from placement in the bay to first grading. The outcome of interest was cumulative batch-level mortality (%). Environmental data at high and low mortality sites were compared, and a risk factor analysis, using a multiple linear regression mixed effects model, was conducted. Cumulative batch mortality ranged from 2% to 100% (median = 16%, interquartile range: 10–34%). The final multivariable risk factor model indicated that batches imported from French hatcheries had significantly lower mortalities than non-French hatcheries; sites which tested negative for OsHV-1 μvar during the study had significantly lower mortalities than sites which tested positive and mortalities increased with temperature until a peak was reached. There were several differences between the seed stocks from French and non-French hatcheries, including prior OsHV-1 μvar exposure and ploidy. A range of risk factors relating to farm management were also considered, but were not found significant. The relative importance of prior OsHV-1 μvar infection and ploidy will become clearer with ongoing selection towards OsHV-1 μvar resistant oysters. Work is currently underway in Ireland to investigate these factors further, by tracking seed from various hatchery sources which were put to sea in 2012 under similar husbandry and environmental conditions.
    • Viral gametocytic hypertrophy of the Pacific oyster Crassostrea gigas in Ireland

      Cheslett, D.; McKiernan, F; Hickey, C; Collins, E (Inter Research, 2009)
      Viral gametocytic hypertrophy (VGH) was detected during an investigation of mortalities in Pacific oysters Crassostrea gigas from 2 separate Irish production sites. The basophilic inclusions were observed in the gonad tissue of oysters sampled in August and October 2007. The oysters involved did not show any macroscopic disease signs. Transmission electron microscopy demonstrated the presence of viral particles in these intranuclear inclusions. The particles were small, non-enveloped, icosahedral and approximately 50 nm in diameter and thus had characteristics similar to the Papillomaviridae and Polyomaviridae families. No host defence reaction was observed. The viral particles described here appear to be similar to those described in C. virginica from the USA and Canada and to those described in C. gigas from Korea and France.