Comparative Studies On Morphology And Genetics Of Chinese And Japanese White Croaker (Pennahia Argentata)

Pennahia argentata, commonly called white croaker, is one of the economically important sciaenid species and widely distributed in northwestern Pacific, ranging from Tohoku, Japan to Guangdong, China. White croaker is a demersal fish that inhabits sandy or muddy bottoms in coastal and a major component of demersal fish assemblages off the coasts of China and Japan, supporting an important commercial fishery. In order to detect the genetic differentiation and divergence of Chinese and Japanese white croaker, morphological method and complete mitochondrial DNA sequences were studied.Twenty-two morphological characters of populations of white croaker from Zhoushan, Guangzhou (China) and Ise Bay (Japan) were analysed by PCA (principal component analysis), clustering, and one-way ANOVA. All above analysis indicated significant genetic divergency existed between Chinese and Japanese white croaker and four characters differentiated to subspecies level by the criteria of C.D≥1.28.Seven otolith morphological characters of two white croaker populations from Guangzhou (China) and Ise Bay (Japan) were analysed by PCA and one-way ANOVA and four characters differentiated to subspecies level by the criteria of C.D≥1.28.Our study showed that there was a certain extent of geographical variances between Chinese and Japanese pulations of white croaker from both traditional and otolith morphological perspective.In this study,37 pairs of primers was designed and used in PCR and sequencing. Through primer walking sequencing and sequnce assembly, the complete mitochondrial genome sequences of white croaker was obtained. The mitogenome length of Chinese and Japanese white croaker is 16491 bp and 16486 bp, respectively. The genome contains 22 transfer RNA genes (tRNA),2 ribosomal RNA genes (rRNA),12 protein-coding genes,1 control region and 1 dominating noncoding region. Of the 37 genes,28 genes (with the exception of tRNA-Pro, tRNA-Glu, tRNA-Ser, tRNA-Tyr, tRNA-Cys, tRNA-Asn, tRNA-Ala, tRNA-Gln and ND6) are encoded on the heavy strand. The nucleotide composition shows a nucleotide bias against G and especially in the twelve protein-coding genes encoded by the H-strand. In the 13 typical protein-coding genes, all the initiation codons have been identified as ATG, and 3 type of stop codon are found, they are TAG, AGA, TAA and some of the stop codons are incomplete, with TA or T. Among the 22 tRNAs, except tRNA-Ser (GCT), the other 21 tRNAs have clover second structure with anticodon loop, TΨC loop and DHU loop. The control region is an AT rich region and also the most variable region in mtDNA. In this study, extended termination associated sequences (ETAS), central conserved domain (CD), and conserved sequence blocks (CSB) are identified in the control region.12S sequences,16S sequences, Cyt b sequence, control region sequences and sequences of 13 concatenated protein-coding genes are used respectively to construct NJ phylogenetic tree, and the results indicates that concatenated genes sequence can complement the defect of single genes, hence it is more resolvable in phylogenetic research. The compare of mitogenome sequences of Chinese and Japanese white croaker shows that relative evolution rates of mtDNA regions:control region>protein-coding genes>rRNA genes. Applying Cyt b divergence rate of 2%/MY, the divergence between Chinese and Japanese white croaker occurred about 950000 years before present (BP) in Late Pleistocene. Pairwise distances among five sciaenid species calculated for complete Cyt b sequence and complete mitochondrial genome show that divergence rate is similar between Cyt b sequence and complete mtDNA sequence.