Many times we hear these two names, but we don't know the meaning.

Gadus Morhua (scientific name)  or Atlantic Cod: 

Atlantic Cod is a fish that lives in deeper waters and is scattered throughout the North Atlantic. 

Gadus Macrocephalus (scientific name)  or Pacific Cod:

Pacific Cod lives in the near-surface waters of the northwestern Pacíficomainly in the continental shelf area and on the continental slopes at a depth of up to 900 meters. 

Difference between the two: 

The morhua is the traditional, tastier and more tender, for the Portuguese palate. More of this origin is sold in Europe.

The macrocephalus is much more fibrous in texture, and therefore better suited for the desired "string" in codfish cakes.

On the other hand, the macrocephalus is best sold in the US market. Probably because it is a country that is partly bathed by the Pacific Ocean, where this species originates.