swordfish vs saltwater fish

swordfish and saltwater fish both are nouns.

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

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

swordfish (noun)	saltwater fish (noun)
large toothless marine food fish with a long swordlike upper jaw; not completely cold-blooded i.e. they are able to warm their brains and eyes: worldwide in warm waters but feed on cold ocean floor coming to surface at night	flesh of fish from the sea used as food
flesh of swordfish usually served as steaks