Morphometrics and Mitochondrial (COI-Based) Molecular Barcoding of Diptychus maculatus Steindachner, 1866, Snow Trout from the Trans-Himalayan Region of Ladakh, India

Abstract

The present study integrates morphometric analysis, length–weight relationship (LWR), condition factor, and mitochondrial COI-based molecular barcoding to elucidate the biological characteristics of Diptychus maculatus and confirm species identity, respectively, from the Trans-Himalayan region of Ladakh, India. A total of 300 specimens, collected from glacier-fed tributaries of the Indus River (Suru and Shingo rivers), were analysed. Twenty-five morphometric traits exhibited strong, significant positive correlations (r = 0.24–0.94), indicating high morphological integration and proportional body growth typical of rheophilic hill-stream fishes. The LWR showed negative allometric growth (b = 2.89, p < 0.01), indicating that length increased relative to weight. The mean Fulton's condition factor (K = 0.91 ± 0.014) reflected a moderate physiological condition in the population. Molecular analysis of the COI gene confirmed species identity, with a similarity of 97%–98% and revealed clear genetic divergence from closely related Schizopygopsinae species. Phylogenetic analyses supported the distinct placement of D. maculatus in relation to its conspecific sequences, highlighting its evolutionary relationships within the high-altitude cyprinid group. This study provides the first comprehensive morphometric and molecular baseline information for D. maculatus from the Trans-Himalayan Ladakh region, offering critical insights for future conservation and management.