sand eel vs spiny-finned fish

sand eel and spiny-finned fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
sand eel	Yes	No	No	No
spiny-finned fish	Yes	No	No	No

As nouns, spiny-finned fish is a hypernym of sand eel; that is, spiny-finned fish is a word with a broader meaning than sand eel:

sand eel: very small silvery eellike schooling fishes that burrow into sandy beaches
spiny-finned fish: a teleost fish with fins that are supported by sharp inflexible rays

Other hypernyms of sand eel include acanthopterygian.

sand eel (noun)	spiny-finned fish (noun)
very small silvery eellike schooling fishes that burrow into sandy beaches	a teleost fish with fins that are supported by sharp inflexible rays