PCR survey for Paramoeba perurans in fauna, environmental samples and fish associated with marine farming sites for Atlantic salmon (Salmo salar L.)

Abstract

Amoebic gill disease (AGD) caused by the amoeba Paramoeba perurans is an increasing problem in Atlantic salmon aquaculture. In the present PCR survey, the focus was to identify reservoir species or environmental samples where P. perurans could be present throughout the year, regardless of the infection status in farmed Atlantic salmon. A total of 1200 samples were collected at or in the proximity to farming sites with AGD, or with history of AGD, and analysed for the presence of P. perurans. No results supported biofouling organisms, salmon lice, biofilm or sediment to maintain P. perurans. However, during clinical AGD in Atlantic salmon, the amoeba were detected in several samples, including water, biofilm, plankton, several filter feeders and wild fish. It is likely that some of these samples were positive as a result of the continuous exposure through water. Positive wild fish may contribute to the spread of P. perurans. Cleaner fish tested positive for P. perurans when salmon tested negative, indicating that they may withhold the amoeba longer than salmon. The results demonstrate the high infection pressure produced from an AGD-afflicted Atlantic salmon population and thus the importance of early intervention to reduce infection pressure and horizontal spread of P. perurans within farms.

Biofouling in marine aquaculture: a review of recent research and developments

“…Vibriosis bacteria have also been found in biofilms on cage nets in Malaysia, where their abundance correlated with outbreaks of the disease (Albert and Ransangan 2013). The parasitic amoeba responsible for amoebic gill disease (AGD) in Atlantic salmon, Paramoeba perurans, is associated with several key biofouling organisms during acute AGD outbreaks, including hydroids, bryozoans, tunicates, and molluscs (Hellebø et al 2017). Although the amoeba's reservoir between outbreaks is still unknown, biofouling organisms could act as reinfection agents for recently treated or uninfected fish in nearby cages.…”

Establishment of a non-invasive method for stress evaluation in farmed salmon based on direct fecal corticoid metabolites measurement

“…The virus test for salmon pancreas disease (PD) in cardiac tissue, and amoebic gill disease (AGD) test in gill tissue, were performed by an accredited commercial firm, PatoGen Analyse AS ( www.patogen.no). Real-time RT qPCR analyses were performed according to accredited procedures of PatoGen Analyse AS [9][10][11]. Table 1 shows the infection rate of AGD and PD in the studied salmon group.…”

Free-living Neoparamoeba perurans depth distribution is mostly uniform in salmon cages, but reshaped by stratification and potentially extreme fish crowding

“…By comparison, limited information exists on the spatio-temporal distribution of free-living N. perurans. In the last decade, N. perurans was confirmed as the disease-causing agent of AGD (Young et al 2007, 2008, Crosbie et al 2012), a molecular method for detecting it in the marine environment was developed (Bridle et al 2010, 2015, Wright et al 2015b, and the first assessments of its free-living distribution in salmon sea-cages were conducted (Bridle et al 2010, Wright et al 2015b, Hellebø et al 2017). These assessments found that N. perurans occurs throughout the water column within farms holding AGD-affected stock in Australia (Bridle et al 2010, Wright et al 2015b) and in Norway (Hellebø et al 2017).…”

“…In the last decade, N. perurans was confirmed as the disease-causing agent of AGD (Young et al 2007, 2008, Crosbie et al 2012), a molecular method for detecting it in the marine environment was developed (Bridle et al 2010, 2015, Wright et al 2015b, and the first assessments of its free-living distribution in salmon sea-cages were conducted (Bridle et al 2010, Wright et al 2015b, Hellebø et al 2017). These assessments found that N. perurans occurs throughout the water column within farms holding AGD-affected stock in Australia (Bridle et al 2010, Wright et al 2015b) and in Norway (Hellebø et al 2017). Further, free-living N. perurans are most abundant when clinical AGD levels are highest in stock and/or water temperatures are elevated (Wright et al 2015b, Hellebø et al 2017, and there have been occasions of higher abundance in the upper cage depths (Wright et al 2015b, Hellebø et al 2017).…”

“…These assessments found that N. perurans occurs throughout the water column within farms holding AGD-affected stock in Australia (Bridle et al 2010, Wright et al 2015b) and in Norway (Hellebø et al 2017). Further, free-living N. perurans are most abundant when clinical AGD levels are highest in stock and/or water temperatures are elevated (Wright et al 2015b, Hellebø et al 2017, and there have been occasions of higher abundance in the upper cage depths (Wright et al 2015b, Hellebø et al 2017). Surface concentrations of N. perurans have been hypothesised to result from either the swimming behaviour of caged salmon or the life history of this amoeba (Wright et al 2015b).…”