Comparative Mitochondrial Features Across Characiformes (Teleostei: Ostariophysi) and Mitogenomic Architecture of Nematobrycon lacortei

Characiformes, a highly diverse group, are of great economic and ecological significance; however, their complex morphological convergence and adaptive radiation pose challenges to taxonomy, and phylogenetic controversies remain. In this study, the complete mitochondrial genome (mitogenome) of Nematobrycon lacortei was sequenced and a comparative analysis within 51 Characiformes mitogenomes was conducted. The mitogenome of N. lacortei was a 17,585 bp circular DNA molecule, with standard organization, and showed an A/T bias with an A + T content of 62.29%. The nucleotide composition analysis of Characiformes mitogenomes revealed consistency, and the A + T content exceeded the G + C content throughout. Analyses of protein-coding genes (PCGs) revealed that purifying the selection dominates their evolution, with ND1 and ND6 having the lowest Ka/Ks values, while ND3 has the highest. Phylogenetic analyses were conducted on 51 mitogenomes from 15 families of Characiformes. The BI and ML trees supported the classification of most families but showed that Curimatopsis evelynae in Curimatidae did not cluster with its family members; in addition, relationships within Characidae were unstable. These findings contribute to the research on the evolution of Characiformes and highlight the need for more mitogenome data from diverse species in order to further clarify their phylogenetic relationships and evolutionary history.