black cod vs butterfish

black cod

noun
  • Synonym of sablefish (Anoplopoma fimbria); (the sablefish is not a species of codfish; but is referred to as cod informally) 

butterfish

noun
  • The sablefish (Anoplopoma fimbria) (the sablefish is not a true butterfish; but is called such informally) 

  • Perciform fish of the family Stromateidae, including the genera Pampus, Peprilus and Stromateus. 

  • A rock gunnel, Pholis gunnellus, an eel-like fish found in the intertidal and subtidal zones of the North Atlantic. 

  • The New Zealand fish Odax pullus, also known as greenbone. 

How often have the words black cod and butterfish occurred in a corpus of books? (source: Google Ngram Viewer )