Experimental induction of mouthrot in Atlantic salmon smolts using Tenacibaculum maritimum from Western Canada.

Mouthrot, or bacterial stomatitis, is a disease which mainly affects farmed Atlantic salmon, (Salmo salar, L.), smolts recently transferred into salt water in both British Columbia (BC), Canada, and Washington State, USA. It is a significant fish welfare issue which results in economic losses due to mortality and antibiotic treatments. The associated pathogen is Tenacibaculum maritimum, a bacterium which causes significant losses in many species of farmed fish worldwide. This bacterium has not been proven to be the causative agent of mouthrot in BC despite being isolated from affected Atlantic salmon. In this study, challenge experiments were performed to determine whether mouthrot could be induced with T. maritimum isolates collected from outbreaks in Western Canada and to attempt to develop a bath challenge model. A secondary objective was to use this model to test inactivated whole-cell vaccines for T. maritimum in Atlantic salmon smolts. This study shows that T. maritimum is the causative agent of mouthrot and that the bacteria can readily transfer horizontally within the population. Although the whole-cell oil-adjuvanted vaccines produced an antibody response that was partially cross-reactive with several of the T. maritimum isolates, the vaccines did not protect the fish under the study's conditions.

Genotyping of Tenacibaculum maritimum isolates from farmed Atlantic salmon in Western Canada.

Mouthrot infections (bacterial stomatitis) have a significant impact on the Atlantic salmon aquaculture industry in Western Canada due to economic losses and fish welfare. Bacteria isolated from lesions in the field have been identified as Tenacibaculum maritimum. Mouthrot is different to classical tenacibaculosis, which is most commonly associated with ulcerative lesions, frayed fins and tail rot. The marine fish pathogen T. maritimum is found worldwide; however, in Western Canada, the knowledge of the genetic profile of T. maritimum is limited. This study looked at increasing this knowledge by genotyping T. maritimum isolates collected from Atlantic salmon from farms in Western Canada. These genotypes were compared to other species of the genus Tenacibaculum, as well as other known sequence types within the species. The Western Canadian isolates belong to two new sequence types within the T. maritimum species. Phylogenetic analysis shows that the isolates form a distinct branch together with T. maritimum NCIMB 2154T separate from other Tenacibaculum type strains, and they are most closely related to strains from Norway and Chile.

Development of a multiplex assay to measure the effects of shipping and storage conditions on the quality of RNA used in molecular assays for detection of viral haemorrhagic septicemia virus.

Abstract In routine diagnostics, real-time reverse transcriptase quantitative PCR (RT-qPCR) has become a powerful method for fish health screening. Collection, transportation, and storage conditions of specimens could dramatically affect their integrity and could consequently affect RT-qPCR test results. In this study, to assess the expression profile of elongation factor 1 alpha (ELF-1α) gene, head kidney (HK) tissues from Atlantic Salmon Salmo salar were exposed at room temperature, 4°C, -20°C, and -80°C as well as in 70% ethanol for 6, 12, 24, 48, and 72 h. Data showed a significant increase of RT-qPCR cycle threshold (Ct) values for ELF-1α ranging from 14.7 to 26.5 cycles for tissues exposed to room temperature. In order to mimic the sample transportation conditions, different temperatures of storage were used and tissue quality was evaluated using ELF-1α gene expression. Data showed that Ct values for ELF-1α increased significantly when the tissues were transported on ice for 2 h, stored at -20°C, thawed on ice for 6 h, and stored again at -80°C. The HK tissues collected from Atlantic Salmon challenged with viral hemorrhagic septicemia virus (VHSV) through intraperitoneal injection were exposed at room temperature for 0, 6, 12, 24, 48, 72, and 96 h. Data showed a good correlation of values for ELF-1α and VHSV Ct although the ELF-1α mRNA of the host degraded faster than the RNA of VHSV. Based on these data, HK tissues could be transported on ice or ice packs without the quality of the tissue being affected when stored at -80°C upon arrival at the laboratory. In addition, 70% ethanol could be used as a preservative for long-distance transportation. For an efficient diagnostic test, a duplex VHSV-ELF-1α was developed and optimized. Data showed that the sensitivity of the duplex assay for VHSV was similar to the singleplex. Received November 25, 2013; accepted February 14, 2014.