Mugil liza vs gray mullet

Mugil liza and gray mullet both are nouns.

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

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

Mugil liza: similar to the striped mullet and takes its place in the Caribbean region
gray mullet: freshwater or coastal food fishes a spindle-shaped body; found worldwide

Other hypernyms of Mugil liza include grey mullet, mullet.

Mugil liza (noun)	gray mullet (noun)
similar to the striped mullet and takes its place in the Caribbean region	freshwater or coastal food fishes a spindle-shaped body; found worldwide
	highly valued lean flesh of marine or freshwater mullet