Limited Experimental Susceptibility of Post-Smolt Atlantic salmon (Salmo salar) to an Emergent Strain of Vibrio Anguillarum Serotype O3

Abstract

Preliminary evidence has showed an emergent serotype O3 (SO3) strain of Vibrio anguillarum to cause mortality in pre-smolt Atlantic salmon (Salmo salar) by injection with >105 colony forming units (cfus). Here, we sought to identify the susceptibility of Atlantic salmon post-smolts to this emergent strain by both injection and cohabitation to better understand transmission risk within cultured salmon and possibly between salmon and Atlantic menhaden (Brevoortia tyrannus), where this strain was identified. We identified that although mortality could be induced with a high-dose (>106 cfus) intraperitoneal injection of the emergent SO3 strain (cumulative mortality of 40%), post-smolt Atlantic salmon were highly refractory to a low dose (<106 cfus; cumulative mortality of 3%) or cohabitation exposure (no mortality). A qPCR assay targeting this strain was developed and analytically validated, revealing the limited presence of bacterial DNA in the spleen of low-dose-injected fish (2/36) and no detections in sampled cohabitants (0/70) across three timepoints during the 27-day challenge. These results suggest that although Atlantic salmon can succumb to high-dose artificial infections with V. anguillarum SO3, the risk of natural transmissibility and susceptibility of Atlantic salmon to this emergent strain is anticipated to be low.