Sinocyclocheilusxiejiahuai (Cypriniformes, Cyprinidae), a new cave fish with extremely small population size from western Guizhou, China.

This study describes a new species, Sinocyclocheilusxiejiahuai sp. nov., discovered within a cave located in Hongguo Town, Panzhou City, Guizhou Province, southwestern China, with the type locality in the Nanpanjiang River basin. Phylogenetic trees reconstructed based on mitochondrial genes show that the new species represents an independent evolutionary lineage with large genetic differences, 1.9%-13.8% in mitochondrial Cyt b, from congeners. Morphologically, this species can be differentiated from the 79 species currently classified under the genus Sinocyclocheilus by several characteristics: absence of horn-like structures and indistinct elevation at the head-dorsal junction, absence of irregular black markings on the body lateral and scaleless, eyes large, eye diameter 13% of head length, dorsal-fin rays, iii, 6½, last unbranched ray strong, with serrations along posterior margin, pectoral-fin rays, i, 13, anal-fin rays, iii, 5, pelvic-fin rays, i, 7, lateral line pores 74, gill rakers well developed, nine on first gill arch, pectoral fins short, tip not reaching to pelvic-fin origin. The number of Sinocyclocheilus species has been increased from 79 to 80 since the description of this new species.