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EVALUATING THE EFFECTS OF ELEVATED WATER CONDUCTIVITY ON THE SOUTHERN REDBELLY DACE (CHROSOMUS ERYTHROGASTER) AT DIFFERENT LIFE HISTORY STAGES
The Blackside Dace (Chrosomus cumberlandensis; BSD) is a federally threatened minnow that has been extirpated from 31 streams in Tennessee and Kentucky since 1978. Although there is strong evidence linking elevated conductivity levels and low BSD occurrence, the mechanistic relationship between the two variables is poorly understood. The goal of this project is to further elucidate proximate explanations for the progressive extirpation and contemporary genetic disjunction of BSD populations using a closely related species, Chrosomus erythrogaster (Southern Redbelly Dace, SRBD). We hypothesize that elevated water conductivity affects reproduction of SRBD and causes sub-lethal effects which contribute to reduced fitness in adults. First, we reconstituted water chemically analogous to streams within the historic range of BSD reflecting varying levels of mining related impairment. Using reconstituted water, we subsequently performed five separate experiments on SRBD at different life stages testing both acute and chronic stress responses to elevated water conductivity. We found a significant negative relationship between water conductivity level and proportion of SRBD egg hatch (GLM; p <0.001, n = 600 eggs from 7 individuals). Our acute, sub-lethal test results support the hypothesis that elevated conductivity elicits an acute stress response from adult SRBD exhibited by detection of significantly elevated waterborne cortisol (ANOVA; F 2,9 = 7.34, p = 0.013, n = 12) as well as increased oxygen consumption (ANOVA; F 2,17 = 11.5, p <0.001, n = 27). Furthermore, evidence of chronic stress to adult SRBD was detected after prolonged exposure to high conductivity; individuals in impaired treatments experienced reduced growth over a five week period compared to controls (ANOVA; F 1,18 = 7.11 , p = 0.016, 95% CI: -0.27, -0.04) and, although not significant, we detected a trend indicating hypothalamic-pituitary-interrenal axis disruption reflected by reduced cortisol response in high conductivity groups (Control: 6.96 ng g-1 60 min-1, SD = 4.6; High conductivity: 4.03 ng g-1 60 min-1, SD = 2.28; T-test; p = 0.16, n = 12). Our results provide the first evidence demonstrating the potential negative fitness costs associated with elevated water conductivity related to surface mining on a representative fish species at multiple life-history stages.