Atlantic salmon Salmo salar and ballan wrasse Labrus bergylta display different susceptibility to clonal strains of Paramoeba perurans

Amoebic gill disease (AGD), caused by the marine amoeba Paramoeba perurans, is an important disease of farmed Atlantic salmon Salmo salar L. in Norway. The use of wrasse as cleaner fish in salmon net pens raises questions about interspecies transmission of pathogens such as P. perurans. In this study, cohabitant transmission of clonal isolates of P. perurans between Atlantic salmon and ballan wrasse Labrus bergylta Ascanius was examined, using isolates originating from both salmon and wrasse. The challenges resulted in AGD in both species, although less severely in wrasse. The amoeba isolate originating from ballan wrasse was more virulent than that originating from salmon, suggesting P. perurans strain-related virulence differences. The isolate originating from salmon showed limited proliferation in bath-challenged wrasse and salmon, and limited transfer to cohabitants. Our results support previous observations suggesting that salmon may be more susceptible to P. perurans and AGD than ballan wrasse. Treatment of P. perurans infection in wrasse is challenging, as it is a strictly marine fish species. In this study, brackish water (