Journal of Fish Biology (2009) 75, 2363–2372 doi:10.1111/j.1095-8649.2009.02446.x, available online at www.interscience.wiley.com Mitochondrial DNA divergence in the critically imperilled pygmy madtom, Noturus stanauli (Siluriformes: Ictaluridae) M. G. Bennett*†, J. Heath Howell‡, B. R. Kuhajda‡ and R. M. Wood* *Department of Biology, Saint Louis University, 3507 Laclede Avenue, St Louis, MO 63103, U.S.A. and ‡Department of Biological Sciences, University of Alabama, P.O. Box 870345, Tuscaloosa, AL 35487-0345, U.S.A. (Received 6 June 2009, Accepted 16 September 2009) The mitochondrial cytochrome b gene was sequenced for six individuals of the pygmy madtom, Noturus stanauli, a globally imperilled catfish, from both known localities in Tennessee (U.S.A.) sep- arated by over 1055 river km. Phylogenetic and population genetic analyses revealed little divergence between these populations for this locus. © 2009 The Authors Journal compilation © 2009 The Fisheries Society of the British Isles Key words: Clinch River; cytochrome b; Duck River; Ictaluridae; population divergence; Tennessee River. INTRODUCTION The pygmy madtom, Noturus stanauli Etnier & Jenkins, is the smallest of the diminu- tive North American madtom catfishes (maximum standard length 36·2 mm; Etnier & Jenkins, 1980). Taxonomically it is placed in the subgenus Rabida (rabida clade sensu Egge & Simons, 2009), containing the (mostly) saddled madtoms with tooth- like serrae on the anterior and posterior portions of the pectoral spines (Taylor, 1969), and within Rabida, in the elegans clade (sensu Egge & Simons, 2009). The species is historically known from only two short stream segments in the Ten- nessee River drainage, one in the Duck River near the mouth of Hurricane Creek (Humphreys County, TN) and the other at the type locality in the Clinch River at Frost Ford (Hancock County, TN), separated by over 1055 river km (Etnier & Jenkins, 1980; Fig. 1). Recent surveys collected one and three individuals at two other localities on the lower Duck River in Hickman County from 1993 to 2002 and one and seven individuals from 1974 to 2007 at two sites near the type locality [Tennessee Valley Authority Regional Natural Heritage Project (TVAHP), unpubl. data]. †Author to whom correspondence should be addressed. Tel.: +1 205 275 1766; fax: +1 314 977 3658; email: micahgbennett@yahoo.com 2363 © 2009 The Authors Journal compilation © 2009 The Fisheries Society of the British Isles