mullet vs bottom-feeder

mullet and bottom-feeder both are nouns.

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

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

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

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

mullet (noun)	bottom-feeder (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	a scavenger that feeds low on the food chain
highly valued lean flesh of marine or freshwater mullet