Mugil curema vs gray mullet

Mugil curema and gray mullet both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mugil curema	Yes	No	No	No
gray mullet	Yes	No	No	No

As nouns, gray mullet is a hypernym of Mugil curema; that is, gray mullet is a word with a broader meaning than Mugil curema:

Mugil curema: silvery mullet of Atlantic and Pacific coasts
gray mullet: freshwater or coastal food fishes a spindle-shaped body; found worldwide

Other hypernyms of Mugil curema include grey mullet, mullet.

Mugil curema (noun)	gray mullet (noun)
silvery mullet of Atlantic and Pacific coasts	freshwater or coastal food fishes a spindle-shaped body; found worldwide
	highly valued lean flesh of marine or freshwater mullet