dolphin vs percoid fish

dolphin and percoid fish both are nouns.

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

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

dolphin: large slender food and game fish widely distributed in warm seas (especially around Hawaii)
percoid fish: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of dolphin include percoid, percoidean.

dolphin (noun)	percoid fish (noun)
any of various small toothed whales with a beaklike snout; larger than porpoises	any of numerous spiny-finned fishes of the order Perciformes
large slender food and game fish widely distributed in warm seas (especially around Hawaii)