Impact of ecologically relevant road salt levels and captivity on redside dace Clinostomus elongatus thermal tolerance and gene expression

Captive breeding for reintroduction is becoming essential for species survival; however, understanding threats such as road salt exposure and thermal regime shifts in historical habitat and how captivity alters the physiology of an organism is important to gauge reintroduction success. To investigate the impact of road salt and captivity on redside dace Clinostomus elongatus , adult fish were exposed for 72 h to ecologically relevant road salt levels (low vs. high). We then assessed thermal tolerance and collected non-lethal gill samples to determine the transcriptional response of stress, immune, growth and metabolism, and markers of endocrine disruption genes after 2 wk (i.e. wild) or 9 mo in captivity (i.e. captive). Low road salt exposure increased thermal tolerance, while the high concentration had no effect. Furthermore, road salt exposure had no impact on transcript abundance. Captivity had no effect on thermal tolerance but resulted in altered gill transcript abundance in all gene groups. Overall, redside dace are tolerant to ecologically relevant levels of road salt, but captivity shifted transcriptional responses that may be important for reintroduction success; therefore, the effect of captivity should not be ignored as a factor in reintroduction studies.