whitefish vs freshwater fish

whitefish and freshwater fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
whitefish	Yes	No	No	No
freshwater fish	Yes	No	No	No

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

whitefish: flesh of salmon-like or trout-like cold-water fish of cold lakes of the Northern Hemisphere
freshwater fish: flesh of fish from fresh water used as food

whitefish (noun)	freshwater fish (noun)
silvery herring-like freshwater food fish of cold lakes of the Northern Hemisphere	flesh of fish from fresh water used as food
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