whitefish vs soft-finned fish

whitefish and soft-finned fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
whitefish	Yes	No	No	No
soft-finned fish	Yes	No	No	No

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

whitefish: silvery herring-like freshwater food fish of cold lakes of the Northern Hemisphere
soft-finned fish: any fish of the superorder Malacopterygii

Other hypernyms of whitefish include malacopterygian, food fish.

whitefish (noun)	soft-finned fish (noun)
silvery herring-like freshwater food fish of cold lakes of the Northern Hemisphere	any fish of the superorder Malacopterygii
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