| Summary: | To prevent the outbreak of pathogenic diseases, the salmonid aquaculture industry relies on the use of vaccines. While traditional, polyvalent, oil-adjuvanted vaccines (AV) are effective, they do not work against all types of pathogens and the vaccination process and vaccine composition can be stressful for individual fish. Continuing advances in technology have led to the development of a new type of pathogen-specific vaccine; a DNA vaccine (DV). While there are many benefits to DVs, including a physiologically less stressful vaccine formulation, a more rapid immune response, and prolonged protection compared to traditional vaccines, the impacts of DVs on the general physiology of fishes, especially when coupled with an AV, are not well understood. To assess these impacts, growth performance, routine metabolic rate (RMR), and immunological responsiveness were examined in Atlantic salmon (Salmo salar, L.) and rainbow trout (Oncorhynchus mykiss, Walbaum) following the injection of a DV. When injected alone, the DV did not affect fish performance parameters. When injected concurrently with an AV, there were general differences in growth performance and RMR, and species-specific differences in immune responsiveness. Concurrent injection of a DV with an AV in Atlantic salmon was associated with a transient decrease in specific growth rate. As well, concurrent injection elicited an increase in lysozyme activity, an antigen-specific increase in specific antibody (Ab) production, and a delay in the production of virus-specific neutralizing antibodies (NAb). In rainbow trout, concurrent injection of a DV with an AV led to a temporary increase in RMR, an increase in lysozyme activity, and an earlier seroconversion of NAbs. To determine the impact of stress on the vaccine-induced immune response, Atlantic salmon were injected with supra-physiological levels of cortisol following concurrent vaccine injection. If cortisol was presented after initiation of the immune response, there was suppression of lysozyme activity and no effect on the production of specific Abs. Although the current research shows that DVs are highly beneficial to the aquaculture industry, it highlights the need for species-specific studies, especially when combining the DV with traditional, polyvalent vaccines. Land and Food Systems, Faculty of Graduate
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