The family Carangidae comprises several commercially important fishery species. Due to evolutionary convergence driven by consistent swimming behaviors, carangids typically exhibit a slender, fusiform, and compressed body morphology. Consequently, morphological identification of these species can be problematic; indeed, numerous cryptic species have been identified through genetic evidence. This project aims to investigate the genetic diversity and population connectivity of carangids, with a specific focus on two congeneric and morphologically similar species: the Japanese scad (Decapterus maruadsi) and the Indian scad (Decapterus russelli). These two near-shore scads are sister species in the phylogenetic tree based on mitogenomic protein-coding genes. While the cold-water D. maruadsi forms a single well-mixed population with a distribution limited to the Northwest Pacific, the widely distributed warm-water D. russelli consists of three partially sympatric populations (Haplogroups 1-3) across the Indo-Pacific Ocean: Haplogroup 1 mainly in the Indian Ocean, Haplogroup 2 throughout the Indo-Pacific Ocean, and Haplogroup 3 in the West Pacific and the East Indian Ocean. Haplogroup 1 is the basal taxon in D. russelli, suggesting the origin of this species in the Indian Ocean, followed by both westward and eastward distribution expansion. Based on the results of neutrality tests and Bayesian Skyline plot (BSP) analyses of mitochondrial Cytochrome C Oxidase I (COI) gene, D. maruadsi and D. russelli Haplogroup 3 experienced historic population expansion events. This structural discrepancy between closely related species has also been reported in co-occurring benthopelagic cutlassfish, suggesting universal historical differentiation events in this area. Further analyses based on microsatellite DNA markers are in progress.
 

Carangidae,population genetics,mitochondrial DNA,microsatellite DNA