Preliminary Understanding of Complexities in Swimming Performance of Common Minnow (Cyprinidae) Taxa

Understanding swimming performance of native freshwater fishes has implications for ecology, conservation, and management. In particular, this type of information has practical importance for improving the understanding of fish dispersal, occurrence, migration, and invasive potential. The objective of this study was to characterize swimming performance of 2 taxa from the comparatively understudied minnow family (Cyprinidae) and test for potential drivers as a function of total length, sex, habitat, morphology, or some combination. The study assessed Spotfin Shiner (Cyprinella spiloptera; n = 66) and Bluntnose Minnow (Pimephales notatus; n = 24) populations from an ontogenic range of male and female individuals from lentic and lotic habitats in Indiana and Ohio. Akaike information criterion (AIC) model selection identified the most parsimonious linear regression model to predict swimming performance of Spotfin Shiner and Bluntnose Minnow independently. Overall, larger Spotfin Shiners were superior swimmers compared with smaller individuals. In both species, individuals having more streamlined heads and elongated caudal regions were better swimmers. Additionally, Spotfin Shiners that were collected from lotic environments were generally better swimmers than individuals from lentic environments. Models did not recover sex-specific effects in either species—or meaningful total length, or habitat effects, in Bluntnose Minnows. Overall, this study provides evidence of a complex series of swimming performance covariates when assessing or understanding performance. This has implications for aquatic population, assemblage, and community ecology as well as management and conservation efforts.

Temperature-dependent performance as a driver of warm-water fish species replacement along the river continuum

Replacement of fish species by their congeners along gradients of stream size is common in warm-water streams, but the causative environmental factors driving this turnover are not fully understood. We used laboratory experiments to test for differences in temperature-dependent egg hatch success and age-0 food ration size for three congeneric cyprinids that differ in abundance along temperature–stream size gradients. Headwater species (Pimephales promelas and Pimephales notatus) had lower thermal optima and narrower thermal breadths for hatch success compared with a river mainstem species (Pimephales vigilax). Temperature sensitivity of ration size was lowest for P. promelas, intermediate for P. notatus, and highest for P. vigilax. Using an empirical stream temperature model, we predicted water temperatures and projected hatch success and ration size for 7974 stream segments in Kansas, USA. Projected hatch success from May to July and ration size from July to September generally matched abundance–stream size patterns, suggesting that increasing temperature along the river continuum may drive replacements among Pimephales species. Our findings combined with evaluations of timing and duration of spawning seasons will improve mechanistic understanding of species replacements along the river continuum.