Meeting Abstract
Adult Pacific salmon species cease feeding at the start of their migration from salt water to fresh water and must use energy reserves to swim against currents, compete for mates, evade predation, and generate immune responses to contend with freshwater pathogens. We quantified the immune response in migrating adult Chinook salmon, Oncorhynchus tshawytscha, at different times and locations during the run using several different assays. We measured the levels of immunoglobulin heavy chain mu and heavy chain tau mRNA transcript in the anterior kidney and found that levels of both secreted and membrane bound forms of the heavy chain either did not diminish or only partially diminished during migration and spawning. We also measured the innate anti-bacterial ability of plasma isolated from fish to prevent the growth of a lab strain of E. coli. Contrary to the humoral immune response, the innate anti-bacterial components of plasma diminished at later time points in the run and after spawning. Fish were also examined for the presence and severity of eight different pathogens in different organs. While pathogen burden tended to increase during the migration, no specific pathogen signature was associated with diminished immune responses. Additionally, diminished immune responses were not due to increased IL-10 production, as transcripts for this cytokine were similar at all time points that were examined. These results suggest that loss of immune functions in adult migrating salmon are part of the life history of Chinook Salmon and are likely induced by diminished energy reserves or hormonal changes which accompany spawning.
