| Summary: | Mouthrot is a major health and welfare problem in farmed Atlantic salmon (Salmo salar) smolts in the Pacific Northwest (West Coast of North America), particularly in the first few months following saltwater transfer. This disease, associated with the bacterium Tenacibaculum maritimum, is the main reason the Atlantic salmon farming industry in this region continues to use antibiotics. Mouthrot results in large economic losses due to direct fish mortality, as well as the cost of treatments and poor performance of treated fish. Affected smolts die with very little external or internal clinical signs other than characteristic small yellow plaques in the mouth. This clinical presentation is visibly different to that of tenacibaculosis, the disease commonly associated with T. maritimum in other regions of the world or in other marine fish species. T. maritimum is the most extensively studied member of the Tenacibaculum genus; however, its role in causing mouthrot in British Columbia (BC) has not been the focus. The main objective of this study was to gain more knowledge about T. maritimum in BC and its connection to mouthrot in the Pacific Northwest, and to make steps towards developing management tools that would help decrease the use of antibiotic treatments and improve fish welfare. Genotyping of T. maritimum isolates collected from natural outbreaks of mouthrot on Atlantic salmon farms in BC showed the presence of two genetic strains of the bacterium based on 11 housekeeping genes. These strains are most closely related genetically to strains collected from lumpsuckers (Cyclopterus lumpus) with skin lesions and Atlantic salmon in Norway, as well as Atlantic salmon gills in Chile. The division of the BC isolates into two genetic groups is further supported by a serological analysis that showed that there are two serological groups that match the genetic strains. Representative isolates from the two identified BC genetic strains were used to develop a bath challenge model with Atlantic salmon smolts, which is ...
|
|---|