Grant: Alliance Grants

Atlantic salmon (AS) aquaculture companies in British Columbia (BC, Canada) are losing millions of dollars each year to 'mouthrot', a variant of the Tenacibaculum-induced bacterial disease 'tenacibaculosis'. Mouthrot often occurs soon after the transport of salmon from freshwater hatcheries to marine net pens. Research has demonstrated that salmon have a depressed immune system during transport, possibly leading to increased disease susceptibility. Little work has investigated if current practices of transferring AS smolts to marine environments leave AS susceptible to disease. The goal of this work is to investigate if altering salinity acclimatization practices used by AS aquaculture companies in BC influences the susceptibility of AS to a local, pathogenic isolate of Tenacibaculum maritimum. 3 groups of AS will be used in this work. Group 1 will experience the conventional industry practice from freshwater to full saltwater (28 ppt). Group 2 will be held at 6 ppt for one-week followed by incremental increasing salinity concentrations for one-month to 28 ppt. Group 3 will be held at 5ppt for one week, before being transferred 28 ppt salinity for the remainder of the acclimatization period. Fish from Group 1 will then be bath-exposed to T. maritimum or a sham, no bacterial bath for 5 hours. Post-exposure, T. maritimum exposed and sham exposed fish will be grouped with naïve cohabitants of each acclimatization practice (Group 1-3) respectively. Sampling will occur during the acclimatization protocol, post-exposure (i.e., immediately, 24 hrs, 96 hrs, post 96 hrs moribund fish), and post-trial. Collected samples include: mortality data, bacterial isolates from infected fish, and various tissues and blood for downstream diagnostic testing such as qPCR, histopathology, and Next Generation Sequencing (NGS). This work will aid in improving our understanding of how AS respond to mouthrot, how the fish's microbiome responds to T. maritimum infection, and if salinity acclimatization alters the susceptibility to of AS to T. maritimum. If acclimatization protocols do influence AS susceptibility to mouthrot, then modified practices may help alleviate morbidity and mortality at net pen sites.