gray mullet vs percoid

gray mullet and percoid both are nouns.

Word	Noun	Adjective	Verb	Adverb
gray mullet	Yes	No	No	No
percoid	Yes	No	No	No

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

gray mullet: freshwater or coastal food fishes a spindle-shaped body; found worldwide
percoid: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of gray mullet include percoid fish, percoidean.

gray mullet (noun)	percoid (noun)
freshwater or coastal food fishes a spindle-shaped body; found worldwide	any of numerous spiny-finned fishes of the order Perciformes
highly valued lean flesh of marine or freshwater mullet