Induction of tenacibaculosis in Atlantic salmon smolts using Tenacibaculum finnmarkense and the evaluation of a whole cell inactivated vaccine

Tenacibaculosis, an ulcerative disease characterised by skin lesions, mouth erosion, frayed fins and tail rot, is a significant fish welfare issue in marine aquaculture worldwide. The disease is a concern to the Atlantic salmon farming industry due to mortality losses and the use of antibiotics. The most commonly isolated bacterium from Northern Norwegian salmon farms during tenacibaculosis outbreaks is Tenacibaculum finnmarkense; however it has not been shown to be the causative agent. This study investigates the role of T. finnmarkense and closely related strains as the possible agent of tenacibaculosis in smolts recently transferred into seawater. The efficacy of whole cell inactivated vaccines using T. finnmarkense was also investigated using the developed challenge model. The results show that T. finnmarkense strain HFJT and strain Tsp.2 are causative agents of tenacibaculosis as it presents in Northern Norway without the need for any pre-stressor or co-infection, and that different strains vary in pathogenicity. The pathogen does not appear to spread easily from fish to fish and more work is therefore required to determine possible reservoirs and/or vectors. Even though a whole cell inactivated vaccine using T. finnmarkense strain HFJT induces an antibody response, this study did not manage to show any protection against tenacibaculosis induced through a bath infection. Future studies need to include determining pathogen-host interactions and identifying possible antigens for vaccine candidates.