Codfish and their relatives (family Gadidae) represent some of the most commercially important species of fish, yet their systematics and evolutionary origins are relatively poorly understood. Molecular phylogenetic analysis of relationships among 14 species of  gadine fishes indicate that the three Pacific species of gadids represent simultaneous invasions of the Pacific Basin from separate phylogenetic lineages. The Pacific tomcod (Microgadus proximus) is more closely related to the navaga (Eleginus navaga) from the Barent's Sea that it is to the congeneric Atlantic tomcod (Microgadus tomcod). The common ancestor of the Pacific and Atlantic species of Microgadus existed well before the opening of the Bering Strait, which implies that the Pacific tomcod is derived from arctic Navaga and that Eleginus should be synonymized with Microgadus.  Arctic cod (Boreogadus) and Walleye Pollock (Theragra) are more closely related to Atlantic cod (Gadus morhua) than is the latter to Pacific cod (G. macrocephalus), so that Theragra and G. macrocephalus represent separate invasions of the Pacific Basin. Molecular divergences are consistent with speciation events coincident with the re-opening of the Bering Strait 3 ~ 4 Million years ago. On the other hand, Greenland cod (Gadus ogac) and Pacific cod  have essentially identical mtDNA sequences; differences between them are less than those found within Atlantic cod. Greenland cod appear to represent a  northward and eastward range extension of Pacific cod, and should be synonymized with G. macrocephalus.

    Work in progress concerns the systematic relationships and morphological evolution of gadines and their closest relatives, the lotines (including the freshwater burbot, Lota lota) and phycine hakes, and the relationships of the Gadidae with other Gadiform families.