• A longitudinal study of amoebic gill disease on a marine Atlantic salmon farm utilising a real-time PCR assay for the detection of Neoparamoeba perurans

      Downes, J.K.; Henshilwood, K.; Collins, E.M.; Ryan, A.; O'Connor, I.; Rodger, H.D.; MacCarthy, E.; Ruane, N.M. (Inter Research, 2015)
      Amoebic gill disease (AGD) is a proliferative gill disease of marine cultured Atlantic salmon Salmo salar, with the free-living protozoan Neoparamoeba perurans being the primary aetiological agent. The increased incidence of AGD in recent years presents a significant challenge to the Atlantic salmon farming industry in Europe. In this study, a real-time TaqMan® PCR assay was developed and validated to detect Neoparamoeba perurans on Atlantic salmon gills and further used to monitor disease progression on a marine Atlantic salmon farm in Ireland in conjunction with gross gill pathology and histopathology. The assay proved specific for N. perurans, with no cross-reactivity with the related species N. pemaquidensis, N. branchiphila or N. aestuarina, and was capable of detecting 2.68 copies of N. perurans DNA μl−1. Although the parasite was detected throughout the 18 mo period of this study, mortality peaks associated with clinical AGD were only recorded during the first 12 mo of the marine phase of the production cycle. The initial AGD outbreak resulted in peak mortality in Week 17, which was preceded by PCR detections from Week 13 onwards. Freshwater treatments were an effective method for controlling the disease, resulting in a reduction in the weekly mortality levels and also a reduction in the number of PCR-positive fish. In comparison to traditional diagnostic methods, our PCR assay proved to be highly sensitive and a valuable tool to monitor disease progression and, therefore, has the potential to provide information on the timing and effectiveness of treatments.
    • Stable isotope analysis of baleen reveals resource partitioning among sympatric rorquals and population structure in fin whales

      Ryan, C.; McHugh, B.; Trueman, C.N.; Sabin, R.; Deaville, R.; Harrod, C.; Berrow, S.D.; O'Connor, I. (Inter-Research, 2013)
      Stable isotope analysis is a useful tool for investigating diet, migrations and niche in ecological communities by tracing energy through food-webs. In this study, the stable isotopic composition of carbon and nitrogen in keratin was measured at growth increments of baleen plates from 3 sympatric species of rorquals (Balaenoptera acutrostrata, B. physalus and Megaptera novaeangliae), which died between 1985 and 2010 in Irish and contiguous waters. Bivariate ellipses were used to plot isotopic niches and standard ellipse area parameters were estimated via Bayesian inference using the SIBER routine in the SIAR package in R. Evidence of resource partitioning was thus found among fin, humpback and minke whales using isotopic niches. Highest δ15N values were found in minke whales followed by humpback, and fin whales. Comparison between Northeast Atlantic (Irish/UK and Biscayan) and Mediterranean fin whale isotopic niches support the current International Whaling Commission stock assessment of an isolated Mediterranean population. Significantly larger niche area and higher overall δ 15N and δ 13C values found in fin whales from Irish/UK waters compared to those sampled in adjacent regions (Bay of Biscay and Mediterranean) suggest inshore foraging that may be unique to fin whales in Ireland and the UK. Isotopic profiles support spatial overlap but different foraging strategies between fin whales sampled in Ireland/UK and the Bay of Biscay. Stable isotope analysis of baleen could provide an additional means for identifying ecological units, thus supporting more effective management for the conservation of baleen whales.