gudgeon vs percoid

gudgeon and percoid both are nouns.

Word	Noun	Adjective	Verb	Adverb
gudgeon	Yes	No	No	No
percoid	Yes	No	No	No

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

gudgeon: small spiny-finned fish of coastal or brackish waters having a large head and elongated tapering body having the ventral fins modified as a sucker
percoid: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of gudgeon include percoid fish, percoidean.

gudgeon (noun)	percoid (noun)
small slender European freshwater fish often used as bait by anglers	any of numerous spiny-finned fishes of the order Perciformes
small spiny-finned fish of coastal or brackish waters having a large head and elongated tapering body having the ventral fins modified as a sucker