sandfish vs percoid fish

sandfish and percoid fish both are nouns.

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

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

sandfish: either of two small silvery scaleless fishes of the northern Pacific that burrow into sand
percoid fish: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of sandfish include percoid, percoidean.

sandfish (noun)	percoid fish (noun)
either of two small silvery scaleless fishes of the northern Pacific that burrow into sand	any of numerous spiny-finned fishes of the order Perciformes
fish of sandy areas of western Pacific and Indian oceans having an angular snout for burrowing into sand