Untangling the taxonomy, ecology and phylogeny of Clupeiformes ichthyoplankton: An integrated approach to inform conservation and management in Vietnam

Abstract

Understanding the diversity, life history, and evolutionary relationships of commercially and ecologically important Clupeiformes fishes is crucial for effective conservation and management, particularly in biodiverse regions like Vietnam. This research addressed these aspects by investigating Clupeiformes ichthyoplankton across four main ecological regions of Vietnam (North, Central, Southeast, and Southwest). Ichthyoplankton samples, including eggs and larvae, were collected from surface and vertical layers during both main and secondary spawning seasons. An integrated approach, combining morphological characteristics and COI mtDNA gene, was employed to identify 17 clupeiforms species and link their developmental stages. This study successfully connected the egg, larval, and early juvenile stages with adult conspecifics for four key species: Anodontostoma chacunda, Hilsa kelee, Escualosa thoracata, and Stolephorus insularis. Phylogenetic analysis of the 17 Clupeiformes species using COI revealed a clear divergence between the two main families (Dorosomatidae, and Engraulidae). To further resolve these relationships, a mitogenome-based phylogenetic analysis was performed, which critically confirmed a paraphyly within the genus Sardinella. For instance, Sardinella fijiensis did not cluster with other Sardinella species but appeared as a sister group to Hilsa kelee. Significant intraspecific variation, both morphological and genetic, was also observed across the different geographical regions and developmental stages examined. By providing detailed insights into early life histories, resolving some taxonomic uncertainties with mitogenome data, and highlighting geographically and ontogenetically structured intraspecific variation, this study offers critical information for refining management units, identifying essential fish habitats, and developing effective conservation strategies for these vital fish resources in Vietnam.