brown trout vs hardhead

brown trout

noun
  • A species of nonmigratory freshwater trout, Salmo trutta, with dark spotted skin, native to Europe and Asia. 

hardhead

noun
  • Any of certain saltwater sciaenid (Sciaenidae) fishes. 

  • Any of several weeds in or formerly classified in the genus Centaurea, particularly Russian knapweed (Acroptilon repens). 

  • A Scottish billon coin circulated in the reigns of Mary and James VI. 

  • Residual ore that failed to melt during a smelting process. 

  • One who is practical or hardheaded. 

  • A brown diving duck, Aythya australis, native to Australia. 

  • Mylopharodon conocephalus of fresh waters in California. 

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