fish vs mullet

fish and mullet both are nouns.

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

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

fish (noun)	mullet (noun)
any of various mostly cold-blooded aquatic vertebrates usually having scales and breathing through gills	bottom dwelling marine warm water fishes with two barbels on the chin
the flesh of fish used as food	freshwater or coastal food fishes a spindle-shaped body; found worldwide
	highly valued lean flesh of marine or freshwater mullet

fish (verb)	mullet (verb)
catch or try to catch fish or shellfish
seek indirectly