herring vs shad

herring

noun
  • Fish in the family Clupeidae. 

  • A type of small, oily fish of the genus Clupea, often used as food. 

  • Fish similar to those in genus Clupea, many of those in the order Clupeiformes. 

shad

noun
  • Any one of several species of food fishes that make up the genus Alosa in the family Clupeidae, to which the herrings also belong; river herring. 

  • The bluefish (Pomatomus saltatrix). 

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