A new loach species of the genus Vanmanenia (Actinopterygii: Cypriniformes: Gastromyzontidae) from hill streams of Vietnam

Recent ichthyofauna surveys in Phia Oac-Phia Den National Park, Vietnam, yielded 16 specimens of loach representing the genus Vanmanenia . These specimens were uniform in morphology and distinct from known species, leading to the designation of a new species, Vanmanenia duci sp. nov. This species is distinguished from congeners by the following combination of characters: pectoral fin: I, 15; pelvic fin: I, 8; lateral line scales 77–83; the distance from the anus to the posterior insertion of the pelvic fin being greater than from the anus to the anal fin origin; a lateral black stripe from the gill opening to the caudal fin base; a black spot at the caudal fin origin equal to the eye diameter; and a lower lip with three large papillae, with the middle one being larger. The new species differs from Vanmanenia caldwelli (Nichols, 1925) by its mouth soft-tissue structures and lower morphometric values and from Vanmanenia ventrosquamata (Mai, 1978) and Vanmanenia caobangensis Nguyen, 2005 by having more lateral line scales and lower body depth. Additionally, Vanmanenia duci sp. nov. has a larger eye and wider interorbital space compared to other species in Vietnam. This species is found in the Red River basin in Vietnam and the Bang Giang River flowing into China, indicating high potential for freshwater fish diversity in these river systems.