tarpon vs soft-finned fish

tarpon and soft-finned fish both are nouns.

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

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

tarpon: large silvery game fish of warm Atlantic coastal waters especially off Florida
soft-finned fish: any fish of the superorder Malacopterygii

Other hypernyms of tarpon include malacopterygian.

tarpon (noun)	soft-finned fish (noun)
large silvery game fish of warm Atlantic coastal waters especially off Florida	any fish of the superorder Malacopterygii