Thunnus vs fish genus

Thunnus and fish genus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Thunnus	Yes	No	No	No
fish genus	Yes	No	No	No

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

Thunnus (noun)	fish genus (noun)
tunas: warm-blooded fishes	any of various genus of fish