sailfish vs saltwater fish

sailfish and saltwater fish both are nouns.

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

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

sailfish (noun)	saltwater fish (noun)
large pelagic game fish having an elongated upper jaw and long dorsal fin that resembles a sail	flesh of fish from the sea used as food
a saltwater fish with lean flesh