Comparative analysis of complete mitochondrial genomes of fourteen moray eels (Anguilliformes: Muraenidae) and primary exploration of their phylogenetic relationship and temperature adaptation.

Moray eels (Anguilliformes: Muraenidae) are commonly found in subtropical and tropical waters, where they favor sheltered habitats and occasionally exhibit aggressive behavior. Nowadays, mitochondrial genomes (mitogenomes) information of moray eels remains poorly understood, and analysis of gene re-arrangements and evolutionary history within Anguilloidei remain largely unknown. In this study, mitochondrial genomes from 12 Gymnothorax spp. and 2 Echidna spp species were sequenced, assembled and annotated, and most of which were not published before. Our results showed that the mitochondrial genomes of the 14 species were approximately 16.5 kb in length, with GC content ranging from 41.1 to 46.1%. The mitochondrial genomes of these 12 Gymnothorax spp. and 2 Echidna spp are circular molecules that encode a total of 37 genes, including 13 protein-coding genes (PCGs), 22 tRNA genes, 2 rRNA (small and large subunit rRNA encoding genes) and a non-coding control region (CR). In addition, three types of gene arrangement have been identified for the first time in the mitogenomes of Anguilloidei. Phylogenetic relationships of 51 moray eel mitogenomes based on the protein-coding genes indicate that mitogenome sequences reveals the higher-order relationships of different Anguilloidei. Gene order and phylogenetic data are valuable for elucidating the evolutionary connections among various Anguilloidei species. Cox3 exhibited the smallest non-synonymous mutation value among all the 13 protein-coding genes, indicating that the role of Cox3 in maintaining energy metabolism under warm water conditions is a hypothesis based on observed evolutionary conservation. The complete information of mitogenomes in these 12 Gymnothorax spp. and 2 Echidna spp species provides genetic markers for species identification and temperature adaptation studies in Anguilloidei.