Pacific lamprey is an important cultural and ecological species to freshwater ecosystems of the Pacific Northwest. Lamprey often rear in low gradient portions of watersheds that have high exposure to climate warming, yet very little is known about their thermal physiology in comparison with other anadromous fishes such as Pacific salmon. Our goal was to characterize the response of larval Pacific lamprey to chronic
heat stress to learn how changing stream temperatures could affect this life stage. Lamprey exposed in the laboratory to temperatures reflective of current summer water temperatures in the Willamette River, OR (20-25°C) did not suffer increased mortality. These animals did not feed substantially in captivity, inadvertently adding a starvation stressor to the experiment. Lamprey held at 22.5-25°C had standard
metabolic rates approximately four times that of lamprey held at 13-25°C, which was associated with greater loss in both body mass and length. Additionally, the results of a differential gene expression (DE) analysis and functional enrichment analysis indicate pathways involved with starvation made up a significant proportion of the deferentially expressed genes at elevated temperatures. These results suggest that larval lamprey are able to resist multiple stressors for extended periods of time but likely at the cost of long term fitness and survival.