mullet vs bottom-dweller

mullet and bottom-dweller both are nouns.

Word	Noun	Adjective	Verb	Adverb
mullet	Yes	No	No	No
bottom-dweller	Yes	No	No	No

As nouns, bottom-dweller is a hypernym of mullet; that is, bottom-dweller is a word with a broader meaning than mullet:

mullet: bottom dwelling marine warm water fishes with two barbels on the chin
bottom-dweller: a fish that lives and feeds on the bottom of a body of water

Other hypernyms of mullet include bottom-feeder, percoid, percoid fish, percoidean.

mullet (noun)	bottom-dweller (noun)
bottom dwelling marine warm water fishes with two barbels on the chin	a fish that lives and feeds on the bottom of a body of water
freshwater or coastal food fishes a spindle-shaped body; found worldwide
highly valued lean flesh of marine or freshwater mullet