Sequence comparison of mtDNA 16SrRNA, COI and Cyt b gene fragments in four species of Gadidae fish

In order to identify differentiation of species of Gadidae fishes and evaluate the genetic variance, sequence comparison of mtDNA 16S rRNA, COI and Cyt b gene fragments were employed for Theragra chalcogramma, Gadus macrocephalus, Micromesistius poutassou and Eleginus gracilis. Nucleotide sequences of 539 bp for 16S rRNA, 601 bp for COI and 385 bp for Cyt b genes were obtained. The percentage of A+T content was high. Sequence analysis indicated that the variation level of intra-species was low. The nucleotide substitution rates of three gene segments arranged from high to low was Cyt b COI 16S rRNA. The estimated time of divergence between G. macrocephalus and T. chalcogramma was about 2.19 million years based on Cyt b gene sequence, which was apparently lower than that between E.gracilis and M.poutassou (about 6.53 million years) . The result indicated a Miocene divergence and a Pliocene divergence of the four species. Based on the genetic distances, NJ phylogenetic tree was made and indicated that there was a closer relationship between G. macrocephalus and T. chalcogramma.