The Complete Mitochondrial Genome of Stromateus stellatus (Scombriformes: Stromateidae): Organization, Gene Arrangement, and Phylogenetic Position Within the Suborder Stromateoidei

Background/Objectives: The butterfish Stromateus stellatus is undervalued and usually discarded as bycatch, leading to an inefficient and unsustainable use of marine biomass. Overall, although Stromateus is the type genus of the family Stromateidae, its species are less studied than more economically important fishes. Methods: In this study, we determined and analyzed the complete mitochondrial genome sequence of S. stellatus. Furthermore, we performed maximum likelihood and Bayesian inference analyses to infer the phylogenetic relationships among 21 species of the order Scombriformes. Results: Using next-generation sequencing (NGS) and de novo assembly, a circular mitochondrial genome of 16,509 bp was obtained, exhibiting the typical vertebrate mitochondrial structure comprising 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes. Three intergenic regions were identified, including the control region and the origin of light-strand replication, along with several gene overlaps. The heavy strand nucleotide composition was determined to be 28.79% A, 27.84% C, 16.32% G, and 27.05% T, with a GC content of 44.16%. The three Peprilus and five Pampus species formed a clade together with S. stellatus, supported by high bootstrap and posterior probability values, confirming the monophyly of Stromateidae. Conclusions: The gene order and content are consistent with those reported for other Stromateidae species and correspond to the typical arrangement observed in most bony fishes. This mitochondrial genome represents the first one reported for the genus Stromateus, providing valuable insights into the genetic makeup of S. stellatus, contributing to a better understanding of marine biodiversity. Additionally, these data will support future research on pelagic fish evolution and assist in sustainable fisheries management.