food fish vs fish

food fish and fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
food fish	Yes	No	No	No
fish	Yes	No	Yes	No

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

food fish: any fish used for food by human beings
fish: any of various mostly cold-blooded aquatic vertebrates usually having scales and breathing through gills

food fish (noun)	fish (noun)
any fish used for food by human beings	any of various mostly cold-blooded aquatic vertebrates usually having scales and breathing through gills
	the flesh of fish used as food

food fish (verb)	fish (verb)
	catch or try to catch fish or shellfish
	seek indirectly