burbot vs cusk

burbot

noun
  • A freshwater fish, taxonomic name Lota lota, which is similar to the ling and the cusk and spawns in the winter. 

cusk

noun
  • A marine cod-like fish in the ling family Lotidae, Brosme brosme. 

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