Abstract Cryptic diversity in mesopelagic fish is increasingly documented across the Indo-Pacific, but remains understudied in the Red Sea, a region known for its high endemism and unique ecological conditions. We investigated cryptic diversity in Benthosema spp. and population genetic structure in the two most abundant mesopelagic fishes in the eastern Red Sea, the Benthosema pterotum species complex and the endemic Vinciguerria mabahiss . Using concatenated mitochondrial ( 12S , 16S , and COI ) sequences from 275 V. mabahiss and 84 Benthosema specimens, we detected panmictic populations in both species. Both species showed high haplotype diversity and signatures of recent demographic expansion, supported by star-like haplotype networks, negative neutrality tests, and Bayesian skyline plots. Phylogenetic analysis revealed a cryptic lineage ( Benthosema cf. pterotum ) in the eastern Red Sea, forming a sister lineage within the genus. Its genetic similarity with Gulf of Oman populations suggests ongoing gene flow through the Strait of Bab-el-Mandeb. These findings challenge current taxonomic frameworks and highlight the importance of accurate species delimitation for biodiversity monitoring and fisheries management. High genetic connectivity and demographic expansion in both mesopelagic fish species suggest resilience driven by large effective population sizes and high dispersal potential. These results provide the first population genetic baseline for the largest fish stock in the eastern Red Sea and support future efforts to assess adaptive potential in a warming marginal sea.
Lim et al. (Tue,) studied this question.