Arctic Grayling are Holarctic species, with only one native population in the contiguous United States, located in the Big Hole River, Montana. Habitat changes and climate effects have contributed to a gradual rise in mean water temperatures over the last 20 years. This study aimed to assess how different water temperatures will affect Arctic Grayling survival, growth, as well as to estimate a thermal performance curve (TPC) and the enzyme activity and gene expression related to stress responses.
Over a 144-day trial, juvenile Arctic Grayling were exposed to temperatures ranging from 8°C to 26°C. Growth, TPC, survival, gene expression, and antioxidant enzyme activities were estimated across these temperature conditions. Fish exhibited increased growth rates as temperatures rose to 18°C, after which growth sharply declined. No fish survived at temperatures above 22°C. The growth and survival results corresponded with the TPC where the optimal temperature of growth was estimated to be 16.96 °C. The minimum temperature was estimated at 4.87°C and the maximum temperature where growth is projected to cease was estimated at 23.18 °C. Moreover, temperatures above 16°C led to a 3.0-fold increase in superoxide dismutase (SOD) gene expression and a 1.5-fold increase in glutathione peroxidase (GPx) expression, reflecting increased oxidative stress. However, no significant changes were observed in the ratio of heat shock protein 70 (HSP70) to heat shock protein 90 (HSP90) gene expression. And no clear pattern was observed in the expression of catalase (CAT) Enzyme activities for SOD and GPx also increased at higher temperatures, corresponding with the gene expression patterns. Thiobarbituric acid reactive substances (TBARS) increased correspondingly with rising temperatures.
These results highlight the sensitivity of Arctic Grayling to even small increases in water temperature, suggesting that further warming could critically endanger their survival in the Big Hole River.