Experimental Induction of Tenacibaculosis in Atlantic Salmon (Salmo salar L.) Using Tenacibaculum maritimum, T. dicentrarchi, and T. finnmarkense

Abstract

There is a limited understanding of the pathogenesis of tenacibaculosis in Atlantic salmon (Salmo salar L.) and there are few reproducible exposure models for comparison. Atlantic salmon were exposed via bath to Tenacibaculum maritimum, T. dicentrarchi, or T. finnmarkense, and were then grouped with naïve cohabitants. Mortalities had exaggerated clinical signs of mouthrot, a presentation of tenacibaculosis characterized by epidermal ulceration and yellow plaques, on the mouth and less frequently on other tissues. Histopathology showed tissue spongiosis, erosion, ulceration, and necrosis ranging from mild to marked, locally to regionally extensive with mats of intralesional bacteria on the rostrum, vomer, gill rakers, gill filaments, and body surface. Exposure to T. maritimum resulted in less than a 0.4 probability of survival for both exposed and cohabitants until Day 21. Exposures to T. dicentrarchi resulted in 0 and 0.55 (exposed), and 0.8 and 0.9 (cohabitant) probability of survival to Day 12 post-exposure, while T. finnmarkense had a 0.9 probability of survival to Day 12 for all groups. This experimental infection model will be useful to further investigate the pathogenesis of tenacibaculosis, its treatment, and immunity to Tenacibaculum species.

Genomics of Tenacibaculum Species in British Columbia, Canada

“…Type IX secretion systems are described in other Tenacibaculum assemblies of T. maritimum NCIMB 2154 T [ 7 ], T. finnmarkense AY7486TD [ 10 , 70 ], T. dicentrarchi isolates [ 59 ], T. piscium isolates [ 12 ] and T. ovolyticum To-7Br [ 8 , 9 ], and therefore could be conserved within the genus. Previous T. maritimum NCIMB 2154 T exposure studies induced less than 30% mortality in Atlantic salmon under select conditions [ 2 ], but other Canadian T. maritimum isolates caused greater mortality, including TmarCan15-1 (100 and 75% mortality in shedders [S] and cohabitants [C]), TmarCan16-1 (100% mortality in S and C), TmarCan16-5 (>80 and 30% mortality in S and C) and T. maritimum 2.1C (barcode 9) (>70 and >60% mortality in S and C) [ 2 , 4 ]. The observed pathogenicity of T. maritimum 2.1C (barcode 9) could be related to the presence of type IV and VI secretion system proteins, suggesting that more work is needed to establish how virulence factors among the Tenacibaculum species are transported.…”

“…Tenacibaculum is a genus of Gram-negative bacteria that are ubiquitous in marine environments and have beneficial, neutral, or negative interactions with marine organisms [ 1 ]. Experimental exposures and circumstantial evidence indicates multiple species of Tenacibaculum as the causative agents of disease in fishes of economic or cultural significance (e.g., salmonids [ 2 , 3 , 4 ], temperate basses [ 5 ], and flatfishes [ 6 ]). Fishes affected by ‘tenacibaculosis’ often display epidermal lesions that can be accompanied by the development of yellow plaques and abnormal behaviours [ 1 ].…”

“…Fishes affected by ‘tenacibaculosis’ often display epidermal lesions that can be accompanied by the development of yellow plaques and abnormal behaviours [ 1 ]. The signs and severity of tenacibaculosis appear to depend on the species or strain of Tenacibaculum [ 2 , 3 , 4 ]; the host species, health-status, and life-stage; and the environmental conditions. In British Columbia (BC), Canada, a regional presentation of tenacibaculosis called ‘mouthrot’ presents as oral plaques and ulcerations on Atlantic salmon ( Salmo salar L.).…”

Tenacibaculosis in wild-caught, captive Chinook salmon (Oncorhynchus tshawytscha) in British Columbia, Canada

“…For Atlantic salmon in BC, tenacibaculosis often presents with yellow-pigmented plaques in the oral cavity and gills of fish, and can lead to cumulative mortality upwards of 40% in infected marine net pens (Frisch et al, 2018; Wynne et al, 2020). Some authors described this manifestation of tenacibaculosis occurring in Atlantic salmon in BC as “mouthrot” (Frisch et al, 2018; Wade and Weber, 2020; Nowlan et al, 2021b), to give more emphasis to the occurrence of yellow plaques in the oral cavity and ulcerative stomatitis which, in some individuals, appear to be the only clinical sign reported. However, in a minority of cases Atlantic salmon affected by mouthrot can also present with erosion of the skin and fins as well as ulcers (Nowlan et al, 2021b), findings that are consistent with reports of tenacibaculosis in salmonids worldwide (Valdes et al, 2021; Avendano-Herrera et al, 2006; Olsen et al, 2020; Spilsberg et al, 2022).…”

“…These have both been detected on salmon farms, can co-occur with T. maritimum , and may be responsible for some cases of tenacibaculosis (Alvarez and Santos, 2018; Avendaño-Herrera et al 2016; Smage et al, 2016, 2018; Olsen et al, 2017; Mimeault et al, 2020). On Atlantic salmon in BC, at least six species of Tenacibaculum have been confirmed, including T. maritimum, T. dicentrarchi and T. finnmarkense (Smage et al, 2018; Nowlan et al 2021a, b; Nowlan et al,2023). The latter three species have been established through international challenge studies as causal agents of tenacibaculosis (Smage et al, 2018; Frisch et al, 2018; Klakegg et al, 2019; Nowlan et al, 2021b; Valdes et al, 2021).…”