Taxonomic assessment of the glyptosternoid catfish Parachiloglanis hodgarti (Hora, 1923) based on morphometric analysis of type specimens and riverine populations in Nepal.

This study addresses a major gap in knowledge regarding intraspecific morphological variation in Parachiloglanis hodgarti (Hora, 1923) (Sisoridae) by conducting comparative morphometric analyses of populations from Nepal's principal river drainages (Gandaki, Koshi and Karnali), the topotypic population from Pharping, and the holotype to evaluate the taxonomic implications of this variation. Eighteen size-corrected morphometric traits were analysed in 108 specimens collected from Pharping (n = 24), Gandaki (n = 28), Koshi (n = 28) and Karnali (n = 28). Principal component analysis (PCA) and linear discriminant analysis (LDA) revealed pronounced population structuring, with the Karnali population showing the strongest multivariate differentiation. Variation among populations was primarily associated with body proportions, head morphology and fin morphology. Univariate analyses detected significant differences in individual morphometric traits among populations, with Pharping showing the highest number of significantly differentiated traits and Gandaki the fewest. Comparisons with the holotype revealed morphometric differences across all populations. Although the Karnali population differed from the holotype in the greatest number of traits (11), it differed from the Pharping topotypic population in only three traits. Because the Pharping topotypic population represents the closest extant proxy for the holotype and closely resembles it in overall morphometric characteristics, the greater divergence between Karnali and the holotype is likely attributable to preservation-related deformation, historical and contemporary differences in measurement protocols, or both, rather than genuine taxonomic differentiation. Collectively, these findings demonstrate geographically structured morphological variation while supporting continuous intraspecific differentiation rather than discrete taxonomic separation. The morphological differentiation observed in the Karnali population may reflect localised evolutionary divergence associated with geographic isolation and environmental heterogeneity, although confirmation will require integrative molecular and ecological investigations. This study establishes a population-level morphometric framework for P. hodgarti in Nepal and provides a baseline for future taxonomic, evolutionary and ecological research.