tarpon vs tarpum

tarpon

noun
  • Any of several fishes of the family Elopidae or Megalopidae, especially a large silvery game fish. 

tarpum

noun
  • A large marine fish (Megalops atlanticus) of the southern United States and the West Indies, with large silvery scales. 

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