codfish vs saltwater fish

codfish and saltwater fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
codfish	Yes	No	No	No
saltwater fish	Yes	No	No	No

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

codfish: lean white flesh of important North Atlantic food fish; usually baked or poached
saltwater fish: flesh of fish from the sea used as food

codfish (noun)	saltwater fish (noun)
major food fish of Arctic and cold-temperate waters	flesh of fish from the sea used as food
lean white flesh of important North Atlantic food fish; usually baked or poached