tunny vs saltwater fish

tunny and saltwater fish both are nouns.

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

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

tunny: important warm-water fatty fish of the genus Thunnus of the family Scombridae; usually served as steaks
saltwater fish: flesh of fish from the sea used as food

tunny (noun)	saltwater fish (noun)
any very large marine food and game fish of the genus Thunnus; related to mackerel; chiefly of warm waters	flesh of fish from the sea used as food
important warm-water fatty fish of the genus Thunnus of the family Scombridae; usually served as steaks