Complete Mitochondrial Genome of Turrum coeruleopinnatum Provides Phylogenetic Context and Candidate Selection Signals Within Carangidae.

The complete mitochondrial genome of Turrum coeruleopinnatum was sequenced and characterized to expand mitogenomic resources for Carangidae and to evaluate its phylogenetic placement and candidate selection signals. The circular mitogenome was 16,553 bp in length and contained 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes, and one control region. Its overall A + T content was 54.04%, and the gene arrangement was consistent with the conserved vertebrate mitochondrial organization. Most tRNAs exhibited typical cloverleaf secondary structures, whereas trnS1 lacked the dihydrouridine arm. A maximum-likelihood tree inferred from the concatenated amino-acid sequences of 13 mitochondrial protein-coding genes provided a mitochondrial phylogenetic context for T. coeruleopinnatum within Carangidae.PAML branch-site analyses identified candidate gene-level signals in atp6, cytb, nad3, and nad5. Four representative residues (ATP6-126T, ND3-94 L, ND5-438 V, and ND5-520 S) were retained because the corresponding gene-level likelihood-ratio tests were significant and their Bayes empirical Bayes posterior probabilities were at least 0.90. Complementary HyPhy analyses showed limited concordance: MEME detected six episodically selected sites that did not overlap with the four retained PAML candidates, FEL detected no sites under pervasive positive selection and indicated widespread purifying selection, BUSTED detected no significant gene-wide episodic diversifying selection, and aBSREL identified only limited branch-level signals. Foreground-background residue comparisons and predicted topological contexts provided descriptive biochemical and spatial information but did not establish functional or adaptive effects. These residues should therefore be regarded as candidate sites requiring further comparative and functional validation.