The Complete Mitochondrial Genomes Of Six Catfishes (Siluriformes)and The Phylogenetic Relationships Analysis

As one of the most important economic species of freshwater fish, the Siluriformes is widely distributed in China and accounting for almost one-third numbers of the entire freshwater for its prominent adaptability to environment. Recent decades, researchers had done lots of works to clarify the relationship among species of Siluriformes, however, the phylogenetic relationship are still unkown in species and intergeneric of Siluriformes. Accordingly, the phylogenetic relationship of Siluriformes has become one challenging and attractive problem to evolutionary biologists and taxonomists.So far, the phylogenetic relationship of Siluriformes in family and genus have some controversy.The early phylogenetic studies of Pelteobagrus and Silurus were mainly based on partial genes and fragments of the mitochondrial genome such as Cytb, ND4and D-loop in which information is very limited. In order to clarify the phylogeny relationship within Siluriformes, the complete mitochondrial genomes were used to do the phylogenetic analysis. In this study, the complete mitochondrial genome sequence of Pelteobagrus fulvidraco, Pelteobagrus vachellii, Pelteobagrus nitidus, Pelteobagrus eupogon, Silurus meridionails and Silurus asotus were determined by using PCR and analyzed using some bioinformatics software. Compared newly obtain mitochondrial DNA sequences with other Siluriformes in the public databases, we expected to elucidate the phylogenetic relationship among different species of Siluriformes.. The main results of our study are as followed:1.The complete mitochondrial genomes of Pelteobagrus fulvidraco, Pelteobagrus vachellii, Pelteobagrus nitidus, Pelteobagrus eupogon, Silurus meridionails and Silurus asotus were16527bp,16527bp,16532bp,16562bp,16527bp and16523bp in length, respectively. These mitochondrial genomes consist of thirteen protein-coding genes (ND1、 ND2、ND3、ND4、ND4L、ND5、ND6、COX1、CoX2、COX3、ATPase6、ATPase8and Cytb), and twenty-two tRNA genes, two rRNA genes(12SrRNA and16SrRNA) and one noncoding region(D-Loop). These genes arrangements in the six catfishes mitochondrial genones were consistent to that of others known Siluriformes.2. Base composition of six siluriformes fish in the mitochondrial genome are shown AT bias. The average A+T content is57.4%which is higher than G+C. In the six catfishes, the highest of A+T content is Pelteobagrus fulvidraco (59.1%), and the lowest is Silurus meridionails (57.4%). The average of A+T content in thirteen protein genes is56.84%, the highest is Pelteobagrus nitidus (58.95%) and the lowest is Silurus meridionails (54.97%) The A+T content were the highest in the third position than that of the first and second position, and that of Pelteobagrus nitidus is the highest in these six catfishes. The G content is the lowest in four bases (A, T, G and C), especially Pelteobagrus eupogon was8.73%only.3. The total length of thirteen peotein-coding genes in the six catfishes (Siluriformes) range from11404(Silurus asotus) to11411bp (Silurus meridionails). Four catfishes (Pelteobagrus) have same length (11408bp). ND5is the longest gene in the13protein-coding genes,which is1824bp in five catfishes except Silurus asotus, and ATPase8is the shortest one, which is168bp in length. All protein-coding genes in Pelteobagrus fulvidraco, Pelteobagrus vachellii, Pelteobagrus eupogon and Silurus meridionails share the same start codon ATG except COX1, which begins with GTG. Eight protein-coding genes in these catfishes used TAA as complete stop condons TAA (ND1、COX1、ATPase6、ATPase8、ND4L、ND5and ND6), but ND2with TAG. The rest five genes end with incomplete stop codons T (COX2, COX3, ND3, ND4and Cytb). And the differcnc in Pelteobagrus nitidus and Silurus asotus, ND2, ATPase6and Cytb end with incomplete stop codons T or TA. NDI gene in Pelteobagrus nitidus and ND5gene in Silurus asotus end with codon TAG.4. Several other conservative sequence elements which occurred in some other fish taxa were identified in the control region of six catfishes (Siluriformes) which containing termination associated sequence(ETAS), conserved sequence blocks (CSB-D、CSB-E、 CSB-F、CSB-1、 CSB-2and CSB-3).5. The intergenic overlaps and spacers range from25bp to28bp and59bp to62bp in length, respectively. The overlaps with a total of28bp is same with that in Pelteobagrus fulvidraco, Pelteobagrus nitidus and Pelteobagrus eupogon. The intergenic spacers were also present in Pelteobagrus nitidus and Pelteobagrus eupogon, Pelteobagrus fulvidraco and pelteobagrus vachellii, Silurus meridionails and Silurus asotus genomes, and involved in a total of59bp,59bp,60bp,60bp,62bp and62bp, respectively. Most of the intergenic overlaps and spacers are very short which is only few nucleotides. The longest spacer with30bp was located between tRNA-Cys and tRNA-Asn and the longest overlapps with10bp was located between ATPase6and ATPase8.6. Based on the three datasets and those phylogenetic analysis results of Siluriformes, the Pelteobagrus fulvidraco and Pelteobagrus eupogon have more close relationships, and the Pelteobagrus vachellii and Pelteobagrus nitidus have the same status.7. According to the phylogeny results, Pseudobagrus brevicaudatus, Pseudobagrus truncatus and Pseudobagrus ussuriensis may belong to Leiocassis which named is Leiocassis brevicaudatus, Leiocassis truncatus and Leiocassis ussuriensis respectively. Pseudobagrus and pelteobagrus were not monophyletic group. The Cranoglanididae and Ictaluridae were sister taxon.