Facing warm temperatures during migration – cardiac mRNA responses of two adult sockeye salmon Oncorhynchus nerka populations to warming and swimming challenges. Oncorhynchus nerka

The main findings of the current study were that exposing adult sockeye salmon Oncorhynchus nerka to a warm temperature that they regularly encounter during their river migration induced an mRNA-level heat shock response that is exacerbated with swimming. Similar immune defense-related responses were also observed. Microarray analyses revealed that 347 genes were differentially expressed between the cold (12-13° C) and warm (18-19° C) treated fish (P < 0.01), with stress response (GO:0006950; P = 0.014) and response to fungus (GO:0009620; P = 0.003) elevated with warm treatment, while expression for genes involved in oxidative phosphorylation (GO:0006119; P = 0.0019) and electron transport chain (GO:0022900; P = 0.00043) increased in cold-treated fish. By studying single genes with RT-qPCR, warm treatment fish from the Chilko population of O. nerka induced expression of heat shock protein (hsp) 90α, hsp90β and hsp30, as well as interferon-inducible protein (P < 0.05). A Nechako population of O. nerka with a narrower thermal tolerance window than the Chilko population showed even more pronounced responses to the warm treatment. In conclusion, it appears that during their once-in-the-lifetime migration these adult sockeye salmon encounter conditions that induce several cellular defense mechanisms. As river temperatures continue to increase, it remains to be seen whether or not these cellular defenses provide enough protection for all sockeye salmon populations. Overall design: Two condition experiment; cold treated fish vs. warm treated fish, n=4 in both group