The complete mitochondrial genome of the whiting, Merlangius merlangus and the haddock, Melanogrammus aeglefinus: a detailed genomic comparison among closely related species of the Gadidae family.

We determined the first complete mitochondrial DNA (mtDNA) sequences for the whiting (Merlangius merlangus, family Gadidae, order Gadiformes) and the haddock (Melanogrammus aeglefinus, family Gadidae, order Gadiformes). The entire mitogenomes were amplified and sequenced by primer walking using newly designed specific internal primers. Lengths were 16,569 and 16,585 bases for whiting and haddock respectively, lengths which lie within the range of previously reported gadiform sequences from Atlantic cod (Gadus morhua, 16,696 bases) and walleye pollock (Theragra chalcogramma, 16,570 bases). Gene arrangement in both species conformed to the order seen in most vertebrate mitochondrial genomes. We identified a long intergenic spacer located between the tRNA(Thr) and tRNA(Pro) genes (of 100 and 70 bp long for whiting and haddock, respectively), as previously described for other species of the order Gadiformes. Using nucleotide and amino acid divergence data of four complete gadoid mitogenomes (M. merlangius, M. aeglefinus, G. morhua and T. chalcogramma), we examined in detail the relative mtDNA mutation patterns across genes and among Gadidae species and tested for the performance of each protein-coding, transfer RNA and ribosomal RNA gene in depicting the expected phylogeny among the four species, as compared with the whole genome dataset. This comparison may be particularly useful in phylogenetic analyses of such a diverse fish family, as well as for the understanding of the patterns of nucleotide substitution of the mtDNA at low levels of divergence.