blennioid fish vs percoid

blennioid fish and percoid both are nouns.

Word	Noun	Adjective	Verb	Adverb
blennioid fish	Yes	No	No	No
percoid	Yes	No	No	No

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

blennioid fish: elongated mostly scaleless marine fishes with large pectoral fins and reduced pelvic fins
percoid: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of blennioid fish include percoid fish, percoidean.

blennioid fish (noun)	percoid (noun)
elongated mostly scaleless marine fishes with large pectoral fins and reduced pelvic fins	any of numerous spiny-finned fishes of the order Perciformes