Minnows and darters are the most imperiled freshwater fish species in North America as a result of habitat degradation and restricted ranges, which often results in isolated populations. The Candy Darter Etheostoma osburni was recently listed as Endangered and may represent a suite of other imperiled fishes in terms of their ecology, life-history traits, and conservation needs. I examined the effects of microhabitat features, sampling effort, species abundance and morphology on riffle-dwelling species. My results confirm many of the well-known influences on detection, while adding to the knowledge of species-specific attributes that can influence detection of common riffle species. Using physical marking and molecular methods, I describe movement patterns and provide insight into the spatial distribution of related pairs and reproductive contribution of the endangered Candy Darter. Minimum detected movements of adults were greater for molecular methods than for visual markings. Indirect movements inferred from the spatial extent between related pairs indicated that parents and offspring move along their entire 18.8-km distribution in Stony Creek, while individual parents and offspring in Laurel Creek move throughout half of their 4.25-km distribution. Additionally, I provide evidence that the lifetime reproductive contribution of Candy Darter is greater than previously described. Using microsatellite DNA markers, I describe population genetic structure and estimate effective population sizes of the four extant populations of Candy Darter in Virginia and provide insight into which populations may be successful as sources for reintroduction or translocation efforts. The four extant populations in Virginia are demographically isolated, but results also suggest historical connectivity. Effective population estimates for all populations were less than the recommended 500 to maintain evolutionary potential, but three populations numbered > 130, indicating they may be viable options for source populations for translocations. My results suggest that all populations may benefit from translocations to overcome genetic drift and inbreeding and to safeguard the historical genetic variation of the species. / Master of Science / Minnows and darters are the most imperiled freshwater fish species in North America as a result of habitat degradation and restricted ranges, which often results in isolated populations. The Candy Darter Etheostoma osburni was recently listed as Endangered and may represent a suite of other imperiled fishes in terms of their ecology, life-history traits, and conservation needs. I examined the effects of microhabitat features, sampling effort, species abundance and morphology on riffle-dwelling species. My results confirm many of the well-known influences on detection, while adding to the knowledge of species-specific attributes that can influence detection of common riffle species. Using physical marking and molecular methods, I describe movement patterns and provide insight into the spatial distribution of related pairs and reproductive contribution of the endangered Candy Darter. Minimum detected movements of adults were greater for molecular methods than for visual markings. Indirect movements inferred from the spatial extent between related pairs indicated that parents and offspring move along their entire 18.8-km distribution in Stony Creek, while individual parents and offspring in Laurel Creek move throughout half of their 4.25-km distribution. Additionally, I provide evidence that adult Candy Darter successfully reproduce over a greater number of years than previously described. Using microsatellite DNA markers, I describe population genetic structure and estimate the number of individuals contributing the gene pool of the four extant populations of Candy Darter in Virginia and provide insight into which populations may be successful as sources for reintroduction or translocation efforts. The four extant populations in Virginia are reproductively isolated, but results also suggest historical connectivity. The numbers of individuals contributing to population-specific gene pools were less than the recommended 500 to maintain evolutionary potential, but three populations numbered > 130, indicating they may be viable options for source populations for translocations. My results suggest that all populations may benefit from translocations to overcome genetic drift and inbreeding and to safeguard the historical genetic variation of the species.