Rastrelliger brachysoma, a short mackerel, is a significant pelagic fish that is common in the fisheries in the Gulf of Thailand. The management of fish stocks is a prerequisite for fish conservation strategies and profitable fisheries. Morphological character differences between stocks of species provide a method for identifying fish stocks. This study was aimed to identify stock population of short mackerel in the Upper and Middle Gulf of Thailand. The fish specimens were collected from four different locations: Chonburi and Prachuap Khiri Khan (central provinces of Thailand), Chumphon and Surat Thani (southern provinces of Thailand). Twelve morphometric characters of fish were assessed to determine the stock populations by stepwise discriminant analysis. The results showed that 12 morphometric characters were significantly different among the four populations. In the discriminant function analysis, the first function explained 61.30% of total variations, whereas the 2nd and 3rd functions were 26.50% and 12.20%, respectively. The characters included total length, standard length, folk length, head length, post – orbital length, pre – dorsal length, pre – pelvic length, 1st dorsal to 2nd dorsal length, pelvic to anal length, pre – anal length, head depth, and greatest depth, all of which can be used to differentiate these populations. According to the results of the discriminant analysis, the populations of short mackerel were predicted and subsequently classified with an accuracy rate of 54.88%.

Rastrelliger brachysoma (short mackerel) and Rastrelliger kanagurta (Indian mackerel) are commercially important marine species in Southeast Asia. In recent years, numbers of these two species have been decreasing in the wild, and genomic information about them is still limited. We conducted a genome survey of these two mackerel species to acquire essential genomic information using next-generation sequencing data. To obtain this genetic information, comprehensive bioinformatics analyses were performed, including de novo assembly, gene prediction, functional annotation, and phylogenetic analysis. The estimated genome sizes were around 680.14 Mbp (R. brachysoma) and 688.82 Mbp (R. kanagurta). The heterozygosity of these species was very similar (≈0.81), while the repeat content for R. kanagurta (9.30%) was slightly higher than for R. brachysoma (8.30%). Functional annotation indicated that most of the genes predicted in these two species shared very close average amino acid identities (94.06%). The phylogenetic analysis revealed close phylogenetic relationships between these two species and other scombrids. This is the first reported genome survey and assembly of species in the genus Rastrelliger and could be useful for future comparative genomic studies.