Mangroves provide an important ecological role as nursery ground for a variety of fishes, including Zenarchopterus dispar (Valenciennes, 1847), a viviparous halfbeak from the Zenarchopteridae family. The early life stages of Z. dispar remain poorly understood due to limited morphological and molecular data. This study combines classical taxonomy and DNA barcoding to characterise the post-flexion and early juveniles of Z. dispar collected from mangrove areas along Vembanad Lake, South-West coast of India, between February 2023 and January 2025. Specimens were recorded exclusively from three out of ten stations, namely Panangad, Kannamaly, and Chellanam, during the pre-monsoon and monsoon seasons, which correspond to optimum environmental conditions. Detailed morphometric and meristic characters revealed diagnostic features such as specific pigmentation patterns including dark dorsal fin and ventral stellate melanocytes, elongated body shape, extended lower jaw and round caudal fin, which were commonly found in post-flexion and early juvenile. But, oval head in post-flexion becomes elongated in early juveniles. The length of the lower jaw is longer in early juveniles than in post-flexion. Partial mitochondrial COI gene sequences confirmed species identity with 100% sequence similarity to Z. dispar submissions in GenBank. Genetic divergence analysis revealed low intraspecific variability (0.6–1.6%) and significant interspecific divergence (11.1–11.9%), supporting clear taxonomic separation. This study provides the first integrative morphological and molecular insights into the early life stages of Z. dispar, which contributes to improved species identification.
