Enhanced immunogenic response of salmonids to Tenacibaculum maritimum formalin-killed vaccine at different water temperatures

Tenacibaculum maritimum is the main organism responsible for yellow mouth (YM) and the primary driver for the use of antibiotics in Canadian Atlantic salmon culture. This creates a potential for the generation of antibiotic-resistant strains and brings significant costs to aquaculture producers. YM only occurs in Atlantic salmon recently transferred to saltwater, wherein affected fish die rapidly with few clinical signs apart from small yellow plaques around the mouth. Interestingly, if fish survive the first three to four months following saltwater transfer, they appear to have long-lasting protection against YM suggesting that immune memory may play a role. As a result, this costly predicament might be solved with an intervention that induces proper immune stimulation prior to the transfer of smolts to saltwater. To explore this, the current study developed an indirect ELISA that was specific for both Atlantic salmon and rainbow trout serum-IgM production towards a North American strain of T. maritimum. This assay was then used to confirm that Atlantic salmon routinely cultured in sea pens develop T. maritimum specific serum IgM and that this antibody development significantly increases over 220 days. To determine whether this antibody production could be induced and possibly optimized, a formalin inactivated T. maritimum vaccine was developed and used for intraperitoneal vaccinations of naïve rainbow trout while being maintained at low (11 °C) and high (15 °C) water temperatures. Analysis of leukocyte recruitment to the injection site revealed that the vaccine significantly enhanced total leukocyte and specifically lymphocyte recruitment when fish were held at the higher water temperature. Pathogen-specific antibody development was also significantly enhanced by the higher water temperature 21 days after receiving the vaccine. However, when a booster was given at day 21, any temperature-related differences in T. maritimum antibody levels between vaccinated groups was eliminated. A better understanding of salmonid antibody development towards T. maritimum could provide valuable insight into the development of an effective vaccine to prevent YM. Such a vaccine intervention could replace currently used antibiotic treatments and drastically improve the sustainability of North American aquaculture.