allis shad vs twaite shad

allis shad

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

twaite shad

noun
  • A fish in the herring family Clupeidae, Alosa fallax, found in the eastern Atlantic Ocean and the Mediterranean Sea. 

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