lake whitefish vs whitefish

lake whitefish and whitefish both are nouns.

Word	Noun	Adjective	Verb	Adverb
lake whitefish	Yes	No	No	No
whitefish	Yes	No	No	No

As nouns, whitefish is a hypernym of lake whitefish; that is, whitefish is a word with a broader meaning than lake whitefish:

lake whitefish: found in the Great Lakes and north to Alaska
whitefish: silvery herring-like freshwater food fish of cold lakes of the Northern Hemisphere

lake whitefish (noun)	whitefish (noun)
found in the Great Lakes and north to Alaska	silvery herring-like freshwater food fish of cold lakes of the Northern Hemisphere
	flesh of salmon-like or trout-like cold-water fish of cold lakes of the Northern Hemisphere
	any market fish--edible saltwater fish or shellfish--except herring