The whole mitochondrial genome sequence of D. boaja had a round genome of 16,562 bp, containing 13 protein-coding genes, 2 rRNA genes, 1 command region and 22 transfer rna genes. The contents of A, C, G, and T were 31.10 %, 24.14 %, 14.36 %, and 30.40 %, respectively. AT and GC contents of mitochondrial genome were 61.50 % and 38.50 %, respectively. The protein code and transfer rna genes of the checkup pipefish mitogenome were predicted using ARWEN ( Laslett and Canback 2008 ). The proportion of coding sequences of D. boaja with a sum length of 11,405 bp was 68.86 %, which encoded 3800 amino acids. All protein-coding genes in D. boaja started with a typical ATG codon, except for COX1 that was initiated by a GTG begin codon. For the stop codon, ND1, ATP8, ATP6, ND4L, ND5, and ND6 genes ended with complete TAA, while the early 7 genes terminated with a one base T or TA. Incomplete stop codon was besides found in the mitochondrial genes of many other fish species ( Yu and Kwak 2015 ; Zhu et alabama. 2018 ). The lengths of 12S ribosomal RNA and 16S ribosomal RNA were 941 bp and 1671 bp, respectively. The 22 transfer rna genes varied from 67 to 74 bp in distance. The tRNA-Ser gene contained a dihydrouridine weapon substitute closed circuit and the other 21 transfer rna genes could be folded into the typical clover-leaf secondary coil structure. exchangeable with most vertebral mitochondrial genome, nucleotide overlaps and space gaps were very common in seahorses and pipefishes ( Cheng et aluminum. 2013 ; Ge et aluminum. 2017 ). The control region locating between tRNA-Pro and tRNA-Phe gene was 948 bp in length, ranging from 15,615 to 16,562 bp.
phylogenetic relationships among D. boaja and other 13 species with accomplished mitogenome sequences were constructed using Solenostomus paradoxus as outgroup. As shown in Figure 1, D. boaja clustered together with Microphis brachyurus with high statistical support, suggesting a relative close relationship between the genus Doryichthys and Microphis. The monophyletic group of D. boaja and M. brachyurus appears deoxyadenosine monophosphate sister to the clade of Doryrhamphus japonicus, indicating that these 3 species shared a more recent coarse ancestor than any early Syngnathidae species. Another checkup pipefish Syngnathoides biaculeatus clustered with Phycodurus eques, while the clade of 5 Hippocampus species was placed as a sister relationship to Corythoichthys flavofasciatus. The data of D. boaja enriched the resource of Syngnathidae in taxonomic, population genetic, and evolutionary biological studies. When the mitogenome representing species from each order in Syngnathidae will be available, the relationship between the species in Syngnathidae will be more clear and accomplished.
calculate 1. Neighbour-joining ( NJ ) tree of 14 species complete mitochondrial genome sequence. The phylogenetic relationships of Doryichthys boaja in Syngnathidae using Sloenostomus paradoxus as the outgroup. Number above each lymph node indicates the ML bootstrap defend values generated from 100 replicates .