Critical current speeds and microhabitats of the benthic fishes Percina roanoka and Etheostoma flabellare

Synopsis Critical current speed (maximum current speed at which benthic stream fishes are able to hold station without active swimming) was determined in a laboratory flow chamber for Percina roanoka and Etheostoma flabellare. Mean critical current speeds differed significantly among adult P. roanoka, adult E. flabellare, and juvenile E. flabellare, and were consistent with microhabitat differences among these darters in natural environments. Behavior of E. flabellare enhanced its station-holding ability, but tests with preserved individuals suggested that morphological differences explained more of the difference in critical current speeds of the darters. On a smooth surface where grasping of the substrate was not possible, use of pectoral fins did not significantly enhance the ability of darters to maintain position in flowing water.