中文摘要：

为检测日本乌鲂Brama japonica与斯氏长鳍乌鲂Taractichthys steindachneri的种间遗传差异,对线粒体16S rRNA、细胞色素b（Cytb）和细胞色素氧化酶Ⅰ（COⅠ）基因片段序列进行了测定。经比对获得同源片段序列的长度分别为491、478、558 bp,其中16S rRNA基因片段上存在2处碱基插入/缺失。核苷酸组成分析结果表明：日本乌鲂与斯氏长鳍乌鲂在这3个基因片段上的G＋C含量差异不显著（P＆gt;0.05）（平均为47.27%、46.59%）,G含量均偏低,特别是在Cytb和COⅠ这两个基因的第三密码子位点上表现尤为突出（平均为9.80%、12.31%）。两种鱼类在线粒体基因组不同片段上的遗传差异比较明显,在总长度为1529 bp的核苷酸序列中,两种间共检测到204处核苷酸替换,两个蛋白质编码基因上的核苷酸替换主要发生在第三密码子位点上;两种鱼类在3个基因片段上的种间净遗传距离依次为0.112 7（16S rRNA）、0.166 4（Cytb）和0.135 3（COⅠ）,遗传差异水平均达到属间差异水平。NJ系统树显示,斯氏长鳍乌鲂与小鳞异鲂Xenobrama microlepis的亲缘关系较近,而与日本乌鲂的亲缘关系较远。根据Cytb基因片段序列分析,日本乌鲂与斯氏长鳍乌鲂的分歧时间约为832万年,两种间分化事件发生在中新世。

英文摘要：

Partial sequences of mitochondrial 16S rRNA,Cytb and COⅠ genes were amplified and sequenced in Pacific pomfret Brama japonica and pomfret Taractichthys steindachneri in order to evaluate the genetic variance in the two species.Three homologous fragments of 491 bp for 16S rRNA,478 bp for Cytb and 558 bp for COⅠ genes were obtained by sequences aligning,and two insertion or deletion of sites were found in the 16S rRNA gene fragment.The nucleotide composition analysis indicated that there was no significant difference in G ＋ C content in the three fragments in the two species（ 47.27% in Pacific pomfret and 46.59% in pomfret）,a strong bias against guanine（ G）,especially in the third codon positions of Cytb and CO Ⅰ genes（ 9.80% in Pacific pomfret and12.31% in pomfret）.Significant difference in genetic variance between the two species was observed in the three mtDNA fragments in which 204 nucleotide substitutions were checked in the total 1529 bp nucleotides analyzed,and nucleotide substitutions in the two protein coding genes were mainly found at the third codon positions.The net genetic distances were 0.112 7 in 16S rRNA,0.166 4 in Cytb,and 0.135 3 in COⅠ gene fragments between the two species,showing intergenus differentiation within family.NJ phylogenetic tree revealed that the relationship between pomfret and Xenobrama microlepis was closer than that between pomfret and Pacific pomfret.It is speculated based on sequence analysis of partial Cytb gene that the divergence between Pacific pomfret and pomfret is derived about 8.32 million years ago,in Miocene.