moonfish vs soft-finned fish

moonfish and soft-finned fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
moonfish	Yes	No	No	No
soft-finned fish	Yes	No	No	No

As nouns, soft-finned fish is a hypernym of moonfish; that is, soft-finned fish is a word with a broader meaning than moonfish:

moonfish: large elliptical brightly colored deep-sea fish of Atlantic and Pacific and Mediterranean
soft-finned fish: any fish of the superorder Malacopterygii

Other hypernyms of moonfish include malacopterygian.

moonfish (noun)	soft-finned fish (noun)
large elliptical brightly colored deep-sea fish of Atlantic and Pacific and Mediterranean	any fish of the superorder Malacopterygii
any of several silvery marine fishes with very flat bodies