Abstract
Glyptothorax hainanensis is a sisorid catfish inhabiting fast-flowing freshwater systems in Southeast Asia. However, biological and genetic information on this species remains limited. In this study, we combined morphological examination, length-weight relationship (LWR) analysis, and mitochondrial COI sequence analysis to support species identification and provide basic biological information about this species in Vietnam. Morphological observations revealed typical external characteristics of the genus Glyptothorax, including a dorsoventrally compressed body, an inferior mouth with well-developed barbels reflecting adaptation to fast-flowing environments. The LWR was described by W = 0.02 × TL²·⁶⁰⁶⁷ (R² = 0.92), indicating a strong length-weight relationship and negative allometric growth. Molecular analysis based on COI sequencing further provided consistent molecular evidence. BLAST comparisons showed the highest sequence similarity with G. hainanensis, and phylogenetic reconstruction placed the studied specimens in the well-supported G. hainanensis clade, clearly distinct from other closely related species. The agreement between morphological, biometric, and molecular supported the identification the classification and highlighted the effectiveness of integrated methods in identifying species in morphologically conserved fish groups. The results of this study provide valuable baseline data on the biology and genetic identity of G. hainanensis, contributing to a better understanding of freshwater fish diversity in Southeast Asia.