fish vs smelt

fish and smelt both are nouns.

Word	Noun	Adjective	Verb	Adverb
fish	Yes	No	Yes	No
smelt	Yes	No	Yes	No

As nouns, smelt is a hyponym of fish; that is, smelt is a word with a more specific, narrower meaning than fish:

fish (noun)	smelt (noun)
any of various mostly cold-blooded aquatic vertebrates usually having scales and breathing through gills	small trout-like silvery marine or freshwater food fishes of cold northern waters
the flesh of fish used as food	small cold-water silvery fish; migrate between salt and fresh water

fish (verb)	smelt (verb)
catch or try to catch fish or shellfish	extract (metals) by heating
seek indirectly