copepod vs fish louse

copepod and fish louse both are nouns.

Word	Noun	Adjective	Verb	Adverb
copepod	Yes	No	No	No
fish louse	Yes	No	No	No

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

copepod: minute marine or freshwater crustaceans usually having six pairs of limbs on the thorax; some abundant in plankton and others parasitic on fish
fish louse: a kind of copepod

Other hyponyms of copepod include brit, britt, cyclops, water flea.

copepod (noun)	fish louse (noun)
minute marine or freshwater crustaceans usually having six pairs of limbs on the thorax; some abundant in plankton and others parasitic on fish	a kind of copepod