The Topeka shiner Notropis topeka is an endangered fish species, historically described as inhabiting cool, headwater prairie streams. However, Topeka shiners recently have been found in off-channel habitats with high temperatures and low concentrations of dissolved oxygen. In laboratory experiments to determine whether Topeka shiners can tolerate the conditions in these off-channel habitats for extended periods, we found that their optimum temperature for growth was approximately 27°C and their critical thermal maximum was 39°C at a 31°C acclimation temperature. Topeka shiners grew at dissolved oxygen concentrations as low as 2 mg/L, but at a considerably lower rate than at 4 mg/L and above. The concentration of dissolved oxygen that was lethal for 50% of the fish after 96 h at 26°C was 1.26 mg/L. Growth was reduced by Asian tapeworm infections. Overall, high temperatures and low dissolved oxygen are probably not limiting factors for Topeka shiner populations in most off-channel habitats.
Bibliographical noteFunding Information:
We are grateful to the Minnesota Department of Natural Resources, Division of Ecological Services, especially Rich Baker, and the U.S. Fish and Wildlife Service, Endangered Species Program, for funding provided under Section 6 of the Endangered Species Act. We also thank Rich Cook and others at the Lost Valley Fish Hatchery (Missouri Department of Conservation) and Scott Campbell with the University of Kansas for providing Topeka shiners. Thanks to Andrew Goodwin of the University of Arkansas for identifying tapeworms and to Drew Mitchell of Stuttgart National Aquaculture Research Center for recommending an appropriate tapeworm treatment. Finally, thanks to many University of Minnesota faculty, staff, and students for statistical advice and laboratory assistance.