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Climate change is increasing water temperature variability, with consequences for small-bodied fishes with limited migratory ability. We assessed seasonal variation in critical thermal maximum and thermal safety margin of an imperilled fish, demonstrating that its physiological ability to manage warming temperatures depends on its recent thermal history., Organisms living in environments with oscillating temperatures may rely on plastic traits to sustain thermal tolerance during high temperature periods. Phenotypic plasticity in critical thermal maximum (CTmax) is a powerful thermoregulative strategy that enables organisms to adjust CTmax when ambient temperatures do not match thermal preference. Given that global temperatures are increasing at an unprecedented rate, identifying factors that affect the plastic response in CTmax can help predict how organisms are likely to respond to changes in their thermal landscape. Using an experimental thermal chamber in the field, we investigated the effect of short-term acclimation on the CTmax and thermal safety margin (TSM) of wild-caught redside dace, Clinostomus elongatus, (n = 197) in a northern population in Two Tree River, Ontario. Streamside CTmax trials were used to identify the maximum temperature at which redside dace maintain equilibrium, providing a powerful tool for understanding how thermal stress affects individual performance. CTmax and TSM of redside dace were sensitive to changes in temperature, regardless of season, suggesting that temperature pulses caused by climate change or urban activities can impose negative fitness consequences year round. Interestingly, an individual’s recent thermal history was more influential to its thermal tolerance than the current ambient water temperature. While the CTmax of redside dace increased with body size, the effect of body size on TSM remains unclear based on our models. The results provide insight into the thermal performance of redside dace that, to date, has been difficult to assess due to the species’ rarity and lack of suitable streamside protocols.

Redside dace Clinostomus elongatus in Minnesota represent genetically unique peripheral populations on the extreme western edge of their native range with uncertain population status. Electrofishing surveys were conducted in 2017 in the Little Cannon River watershed to ascertain life history traits (e.g., age, growth, reproductive traits) for comparison to core populations in eastern North America and to assess population status. Minnesota redside dace grew faster but lived shorter lives than their core populations/counterparts. Females matured at age-2 and about 80 mm total length and males at age-1 and 70 mm. Females produced up to 962 eggs. Estimated population size for age 1+ dace was 9251 (95% C.I. 8300–10,201) and for age 2+ was 6600 (95% C.I. 5789–7411). These values exceeded a demographic minimum viable population estimate of 3305 (nearly double) suggesting that redside dace should persist in this watershed for at least the next two decades (until ≈ 2040).

Environmental DNA (eDNA) detection is increasingly being used to assess the potential presence of aquatic species. Setting defensible thresholds for qPCR assays are necessary to differentiate “detection” from “non-detection”, but threshold rationales are rarely reported in eDNA studies. Detection thresholds for data inclusion and exclusion have implications for downstream data analysis; uncritical acceptance could result in false positive results (Type I error), whereas overly conservative thresholds could result in high false negative interpretation (Type II error). We assessed the use of the receiver operator characteristics (ROC) framework to identify a detection threshold for balancing sensitivity and specificity of eDNA data. The ROC framework was tested using empirical eDNA data from redside dace (Clinostomus elongatus), an endangered freshwater fish in southwestern Ontario. Based on negative controls, positive controls, and quality assurance guidelines, a minimum concentration of 1 copy reaction−1 was identified as the most appropriate threshold for this study. Although optimal thresholds will likely vary between studies and labs based on empirical data, the ROC framework provides a statistical method for establishing defensible thresholds for data acceptance or rejection as well as tradeoffs between the sensitivity and specificity of eDNA data.

The threatened status of redside dace, Clinostomus elongatus, in Michigan inhibits study and management of remnant populations of the species. We present a phenotypic approach to evaluate the use of redside dace from New York as behavioral and physiological models for Michigan populations. We evaluated behavioral similarity by comparing patterns of microhabitat use and physiological similarity by comparing resting routine metabolic rates measured in the field. Variation between sites in available microhabitat made direct comparisons difficult; however, redside dace in Michigan and New York showed a common preference for mid-water positions in the deepest parts of pools under overhanging structure. Field measurements at 10°C showed that Michigan fish had higher metabolic rates than rates predicted for New York fish at the same temperature, though biological significance of this difference is questionable. In laboratory experiments, we measured metabolic rate and upper thermal tolerance in relation to acclimation temperatures of 6–20°C using redside dace collected from four streams in New York. Redside dace showed a significant increase in metabolic rate as acclimation temperature increased (Q10=2.3). Critical thermal maxima (CTM) of New York redside dace also increased with acclimation temperature. Obstacles related to the transferability of habitat use data and variation in physiology due to uncontrolled and unmeasured environmental factors in the field lead us to urge caution when extrapolating behavioral and physiological characteristics between widely-separated populations of a species. Despite these obstacles, we described useful patterns of microhabitat use and provided estimates of physiological tolerances that will assist resource managers in the recovery of Michigan redside dace.

A study was undertaken to examine sperm morphometry in relation to sperm velocity and sperm longevity in the redside dace Clinostomus elongatus. There was significant between-male variance in sperm size and shape metrics (total sperm length, sperm head length, flagellum length and sperm head length to width ratio) and positive relationships were found between these morphometrics and sperm velocity. There were no significant relationships found between sperm morphometry and sperm longevity, nor was there a trade-off between sperm velocity and sperm longevity.

Among the most puzzling records of freshwater fishes from eastern North America is that of Squalius elongatus from Kansas (Hay, 1887: 249). Suspecting that the record was based either on a misidentification or on an intergeneric hybrid, rather than on an example of Clinostomus elongatus (Kirtland), we have not included Kansas in the range of the species (Hubbs and Lagler, 1941: 56; 1947: 64). Since, however, this dace has a markedly localized and disjunct distribution, especially toward the west, and since several northern types range or once ranged southward as far as the Missouri River system in Kansas, the record, though from a stream far removed from others known to be occupied by the species, has not totally lacked plausibility. W. Ralph Taylor on examining the specimen in 1949 determined that it has the pharyngeal teeth alignable in 3 rows, as in most Old-World cyprinids but as in no native North American species. Since this observation accentuated the enigma, I studied the specimen (U.S.N.M. 38233) critically, with the cooperation of Leonard P. Schultz, on January 13, 1951. It was reported by Hay (I.c.) as having been collected by him in the North Fork of Solomon River at Lenora, Kansas, in July, 1885.