bluefin vs tuna fish

bluefin and tuna fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
bluefin	Yes	No	No	No
tuna fish	Yes	No	No	No

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

bluefin: flesh of very large tuna
tuna fish: important warm-water fatty fish of the genus Thunnus of the family Scombridae; usually served as steaks

Other hypernyms of bluefin include tuna, tunny.

bluefin (noun)	tuna fish (noun)
largest tuna; to 1500 pounds; of mostly temperate seas: feed in polar regions but breed in tropics	important warm-water fatty fish of the genus Thunnus of the family Scombridae; usually served as steaks
flesh of very large tuna