Characterizing the Dark Mahseer, Naziritor chelynoides (McClelland, 1839): A Morphological, Osteological, and Molecular Approach

Dark mahseer, Naziritor chelynoides is a vulnerable stream fish in several Asian countries, and developing an effective conservation strategy is impeded by incomplete information about its taxonomy. To address this research gap, in the current study dark mahseer collected from Himalayan stream in India (29°21`99.5` N and 79°33`23.9` E) were examined for their morphometric, meristic, osteological, and molecular characteristics. This study discovered unique features of dark mahseer, including its thin non-hypertrophied lower lip without median lobe, complete post-labial groove, 33 to 34 central perforated lateral line scales, a dark elliptical blotch at the angle of the operculum, and numerous fine black dots on a crescent pattern on scales. This species has 9 to 11 slender gill rakers (595.93±148.71 μm in length), 40 to 41 total vertebrae, 38 to 39 neural spines, 14 to 15 hemal spines, and fused first to fourth abdominal vertebrae. Molecular analysis of cytochrome c oxidase subunit 1 gene (cox1), cytochrome b (cytb), and ATPase subunit 6&8 (ATPase 6&8) genes revealed the genetic distance of 0.08 to 0.10, 0.12 to 0.13, and 0.01 to 0.11 respectively from other Tor species. Our study enhances knowledge of dark mahseer's taxonomy, supporting conservation strategies for this valuable fish species.