Application of Quantitative-PCR to Monitor Netpen Sites in British Columbia (Canada) for Tenacibaculum Species

Abstract

Tenacibaculum are frequently detected from fish with tenacibaculosis at aquaculture sites; however, information on the ecology of these bacteria is sparse. Quantitative-PCR assays were used to detect T. maritimum and T. dicentrarchi at commercial Atlantic salmon (Salmo salar) netpen sites throughout several tenacibaculosis outbreaks. T. dicentrarchi and T. maritimum were identified in live fish, dead fish, other organisms associated with netpens, water samples and on inanimate substrates, which indicates a ubiquitous distribution around stocked netpen sites. Before an outbreak, T. dicentrarchi was found throughout the environment and from fish, and T. maritimum was infrequently identified. During an outbreak, increases in the bacterial load in were recorded and no differences were recorded after an outbreak supporting the observed recrudescence of mouthrot. More bacteria were recorded in the summer months, with more mortality events and antibiotic treatments, indicating that seasonality may influence tenacibaculosis; however, outbreaks occurred in both seasons. Relationships were identified between fish mortalities and antimicrobial use to water quality parameters (temperature, salinity, dissolved oxygen) (p < 0.05), but with low R2 values (<0.25), other variables are also involved. Furthermore, Tenacibaculum species appear to have a ubiquitous spatial and temporal distribution around stocked netpen sites, and with the potential to induce disease in Atlantic salmon, continued research is needed.

Tenacibaculosis caused by Tenacibaculum maritimum: Updated knowledge of this marine bacterial fish pathogen

“…(Apablaza et al, 2017). Similar tenacibaculosis coinfections have been reported in salmon farms in Norway (Olsen et al, 2011;Småge et al, 2016b), Australia (Wilson et al, 2019), and Canada (Nowlan et al, 2021).…”

“…Weight also impacts susceptibility; fish weighing 2-80 g are more susceptible to acute infection, whereas fish over 100 g seem less susceptible (Avendaño- Herrera et al, 2006a). Further influencing infection severity and mortality rates are temperature, water parameters, rearing conditions, stress, and interfering parasitic infestations (Nowlan et al, 2021). In a presumptive diagnosis, the main macroscopic lesions associated with T. maritimum infection are external and include ulcerative skin, tissue necrosis, mouth erosion, tail and fin rots, and necrosis of the gills and eyes [see review by Bernardet (1998); Avendaño-Herrera et al, (2006a)].…”

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

“…Often when a new niche is available for colonization, bacteria that have similar resource requirements will compete, where three long-term consequences are often described (exclusion [a winner], assignment of metabolic niches, or spatial separation of bacteria) [18]. Contamination between tanks could have occurred, potentially through contaminated water, with Tdic as the winner and can be supported by the fact that Tdic is a common isolate from fish with mouthrot in BC [8]. This potential phenomenon requires further investigation, perhaps using dual infections and monitoring isolates over time with qPCR.…”

“…Several Tenacibaculum bacterial species are putative pathogens associated with tenacibaculosis in fishes [1][2][3][4][5][6]. In British Columbia (Canada; BC), Tenacibaculum species are commonly isolated from Atlantic salmon (Salmo salar L.) with mouthrot; a regional, clinical presentation of tenacibaculosis, often characterized by epidermal ulcerations and development of yellow plaques around the mouth [1,[5][6][7][8].…”

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

“…Early research into the causal agent of mouthrot in BC identified Tenacibaculum maritimum as the responsible pathogen (Frisch et al, 2018;Wynne et al, 2020), with experimental trialsusing T. maritimum isolates collected from outbreaks on Atlantic salmon farms in BCsuccessfully inducing mouthrot in exposed Atlantic salmon (Frisch et al, 2018). However, new molecular assays have recently been developed to identify the presence and abundance of other Tenacibaculum species, including T. dicentrarchi and T. finnmarkense (Avendaño-Herrera et al 2016;Smage et al, 2016;Bridel et al, 2018;Nowlan, 2020). 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, 2016Smage et al, , 2018Olsen et al, 2017;Mimeault et al, 2020).…”