ichthyology vs zoology

ichthyology and zoology both are nouns.

Word	Noun	Adjective	Verb	Adverb
ichthyology	Yes	No	No	No
zoology	Yes	No	No	No

As nouns, zoology is a hypernym of ichthyology; that is, zoology is a word with a broader meaning than ichthyology:

Other hypernyms of ichthyology include zoological science.

ichthyology (noun)	zoology (noun)
the branch of zoology that studies fishes	the branch of biology that studies animals
	all the animal life in a particular region or period