pollyfish vs percoid fish

pollyfish and percoid fish both are nouns.

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

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

pollyfish: gaudy tropical fishes with parrotlike beaks formed by fusion of teeth
percoid fish: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of pollyfish include percoid, percoidean.

pollyfish (noun)	percoid fish (noun)
gaudy tropical fishes with parrotlike beaks formed by fusion of teeth	any of numerous spiny-finned fishes of the order Perciformes