bluefin tuna vs tuna fish

bluefin tuna and tuna fish both are nouns.

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

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

bluefin tuna: 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 tuna include tuna, tunny.

bluefin tuna (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