Abstract
ObjectiveArctic Grayling Thymallus arcticus are Holarctically distributed, with a single native population in the conterminous United States occurring in the Big Hole River, Montana, where water temperatures can fluctuate throughout the year from 8 degrees C to 18 degrees C. A gradual increase in mean water temperature has been reported in this river over the past 20 years due to riparian habitat changes and climate change effects. We hypothesized that exposing Arctic Grayling to higher temperatures would result in lower survival, decreased growth, and increased stress responses.MethodsOver a 144-day trial, Arctic Grayling juveniles were subjected to water temperatures ranging from 8 degrees C to 26 degrees C to measure the effects on growth, survival, gene expression, and antioxidant enzyme activity.ResultFish growth increased with increasing water temperature up to 18 degrees C, beyond which survival was reduced. Fish did not survive at temperatures above 22 degrees C. In response to temperatures above 16 degrees C, 3.0-fold and 1.5-fold increases in gene expression were observed for superoxide dismutase (SOD) and glutathione peroxidase (GPx), respectively, but no changes were seen in the gene expression ratio of heat shock protein 70 to heat shock protein 90. Activities of the SOD and GPx enzymes also rose at temperatures above 16 degrees C, indicating heightened oxidative stress. Catalase gene expression and enzyme activity decreased with rising temperatures, suggesting a preference for the GPx pathway, as GPx could also be providing help with lipid peroxidation. An increase in thiobarbituric acid reactive substances was also recorded, which corresponded with rising temperatures.ConclusionOur findings thus underscore the vulnerability of Arctic Grayling to minor changes in water temperature. Further increases in mean water temperature could significantly compromise the survival of Arctic Grayling in the Big Hole River.
The Big Hole River, Montana, contains the only remaining native population of Arctic Grayling in the lower 48 states. This laboratory study shows that higher average water temperatures that accompany climate change and other environmental pertubations will adversely affect the stress and future survival of this population.Impact statement