First cases of amoebic gill disease (AGD) in Norwegian seawater farmed Atlantic salmon, Salmo salar L., and phylogeny of the causative amoeba using 18S cDNA sequences

Abstract

Amoebic gill disease (AGD) was observed in seawater farmed Atlantic salmon at four geographically distant locations on the western coast of Norway. To the best of our knowledge, these are the first detected AGD outbreaks in Norway. The outbreaks lasted for 7-12 weeks in late autumn 2006 and were for the most part concurrent. The crude, cumulative mortality was in the range of 12-20% at three farms and 82% at a fourth. The histopathology showed uniform parasomal amoebae in lesions characteristic for AGD. Another gill disease, proliferative gill inflammation (PGI), was also present to a variable degree and the distinction between the two gill problems is discussed. Seawater temperatures were 3.5 degrees C higher than average before disease outbreaks, which subsided in early winter. The geographical and time pattern of these outbreaks strongly indicates simultaneous infection from the marine environment. Two contiguous 18S cDNA sequences, obtained by reverse transcriptase PCR from gill tissue with AGD-related lesions, showed highest similarity (99.2%) to a newly recognized species designated Neoparamoeba perurans and maximum likelihood analysis demonstrates that they represent Norwegian strains of this Neoparamoeba lineage.

Diseases of farmed Atlantic salmon Salmo salar associated with infections by the microsporidian Paranucleospora theridion

“…This study is the first attempt to gain a more complete picture of the types and numbers of pathogens that can be involved in the development of diseases in Norwegian production of salmonids with a main focus on PGI, PD, HSMI and CMS. These diseases were selected due to the large discrepancies between the observed pathology and mortality in marine already recognised that several pathogens are associated with gill diseases (A. Nylund et al 1998, 2009a,b, Kvellestad et al 2003, Draghi et al 2004, Fridell et al 2004, Todal et al 2004, Callahan et al 2005, Young et al 2007, Steinum et al 2008, and it has also proven difficult to perform challenge experiments with most of these agents. The other 3 diseases, PD, HSMI and CMS, are all associated with the presence of viruses , 2006, Vågenes et al 1999, Nylund 2001, Kongtorp et al 2004a, Bruno & Noguera 2009, Fritsvold et al 2009, Palacios et al 2010, but it is difficult, in challenge experiments, to reproduce both the mortality and all the pathological changes observed during outbreaks in farms.…”

“…Many of the agents that are associated with PGI are commonly found in all areas with salmon farming in Norway; among these are Parvicapsula pseudobranchicola, Ichthyobodo sp., Trichodina spp., SGP virus, and Chlamydia-like species (A. Nylund et al 1998, Todal et al 2004. Neoparamoeba perurans seem to be mainly distributed in western Norway , Steinum et al 2008, while the available information about the geographical distribution of ASPV limits it to the southwest of Norway (Kvellestad et al 2003, Fridell et al 2004. Paranucleospora theridion is present in most parts of Norway with sea production of salmonids (A. Nylund et al 2009a,b, S. Nylund et al 2009.…”

Validating the identity of Paramoeba invadens, the causative agent of recurrent mass mortality of sea urchins in Nova Scotia, Canada

“…Similarly, infection by Paramoeba/Neo paramoeba of farmed salmonids in Tasmania, Australia (Munday et al 1990, Clark & Nowak 1999, DouglasHelders et al 2001, and blue crab Callinectes sapidus in the northeastern US (Johnson 1977), occurs only above threshold temperatures of ~10 and 13°C, respectively. Furthermore, the only documented outbreak of AGD in Atlantic salmon in aquaculture in Norway occurred above a threshold of 11°C and was associated with sea temperatures 3.5°C above the seasonal average (Steinum et al 2008). Given the temperature dependence of Para moeba/ Neoparamoeba-associated disease outbreaks, continued ocean warming could have important implications for the resilience of susceptible host populations.…”

“…Given the temperature dependence of Para moeba/ Neoparamoeba-associated disease outbreaks, continued ocean warming could have important implications for the resilience of susceptible host populations. Indeed, increases in the frequency and severity of outbreaks of sea urchin paramoebiasis and range of AGD are associated with increasing or unusually high sea temperatures in the affected regions (Steinum et al 2008, Scheibling & LauzonGuay 2010.…”

Evaluation of Non-destructive Molecular Diagnostics for the Detection of Neoparamoeba perurans

“…AGD has affected the marine Atlantic salmon industry in Tasmania since the 1980's and has since been described in farmed salmon in Ireland (Rodger and McArdle, 1996), Norway (Steinum et al, 2008), Chile as well as France, Scotland and the Faroe Islands (Rodger, 2014;Oldham et al, 2016). In addition to Atlantic salmon, AGD has also been described in a number of other marine fish species (Oldham et al, 2016) including cleaner fish species used as a biological control of sea lice in Atlantic salmon farms (Haugland et al, in press).…”