Amoeba species colonizing the gills of rainbow trout (Oncorhynchus mykiss) in Swiss aquaculture

Abstract

Nodular gill disease (NGD) is an infectious condition characterized by proliferative gill lesions leading to respiratory problems, oxygen deficiency and mortality in fish. Globally, NGD primarily impacts freshwater salmonids in intensive aquaculture systems. In recent years, numerous outbreaks of severe gill disease have affected more than half of the larger rainbow trout (Oncorhynchus mykiss) farms in Switzerland, mainly during spring and early summer. Mortality has reached up to 50% in cases where no treatment was administered. Freshwater amoeba are the presumed aetiologic agent of NGD. The gross gill score (GS) categorising severity of gill pathology is a valuable first‐line diagnostic tool aiding fish farmers in identifying and quantifying amoebic gill disease (AGD) in farmed marine salmonids. In this study, the GS was adapted to the NGD outbreak in farmed trout in Switzerland. In addition to scoring disease severity, gill swabs from NGD‐affected rainbow trout were sampled and amoeba were cultured from these swabs. Morphologic and molecular methods identified six amoeba strains: Cochliopodium sp., Naegleria sp., Vannella sp., Ripella sp., Saccamoeba sp. and Mycamoeba sp. However, the importance of the different amoeba species for the onset and progression of NGD still has to be evaluated. This paper presents the first description of NGD with associated amoeba infection in farmed rainbow trout in Switzerland.

Identification of new amoebae strains in rainbow trout (Oncorhynchus mykiss, Walbaum) farms affected by nodular gill disease (NGD) in Northeastern Italy

“…Plasmids were purified with a High Pure Plasmid Isolation Kit (Roche Applied Science, Note: MiS and AS were assessed by histological examination. MaS scoring system was modified from the classification method proposed for AGD evaluation of saltwater salmonids (Taylor et al, 2009(Taylor et al, , 2016 and NGD for rainbow trout (Vannetti et al, 2023). MiS and AS follow the method proposed by Perolo et al (2019) and modified from Clark and Nowak (1999).…”

“…Since then, NGD episodes were reported also in Europe, Denmark (Buchmann et al, 2004), Poland (Antychowicz, 2007), Germany (Dyková et al, 2010), the Czech Republic , Italy (Quaglio et al, 2016), Spain (Bermúdez et al, 2019), Russia (Kudryavtsev et al, 2022) and Switzerland (Vannetti et al, 2023).…”

“…It was first described in rainbow trout in Canada (Daoust & Ferguson, 1985, 1986) and in the United States (Bullock et al., 1994). Since then, NGD episodes were reported also in Europe, Denmark (Buchmann et al., 2004), Poland (Antychowicz, 2007), Germany (Dyková et al., 2010), the Czech Republic (Dyková & Tyml, 2016), Italy (Quaglio et al., 2016), Spain (Bermúdez et al., 2019), Russia (Kudryavtsev et al., 2022) and Switzerland (Vannetti et al., 2023).…”

“…GERK, but the direct comparison could not be made due to unpublished sequence data for K77_3F5. Similarly to the study ofVannetti et al (2023), three strains of the genus Ripella were identified. Their sequences could not be compared due to unpublished sequence data of Ripella amoebae inVannetti et al (2023).…”

“…Similarly to the study ofVannetti et al (2023), three strains of the genus Ripella were identified. Their sequences could not be compared due to unpublished sequence data of Ripella amoebae inVannetti et al (2023). Ripella strains identified in our study clustered separately without close relation to known Ripella sequences except for strain CHIESE83/1, showing close relation to Ripella sp.…”