allis shad vs shad

allis shad

noun
  • A herring-like fish (Alosa alosa), of the eastern Atlantic that migrates to fresh water to spawn. 

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 allis shad and shad occurred in a corpus of books? (source: Google Ngram Viewer )