fishbowl vs fish tank

fishbowl and fish tank both are nouns.

Word	Noun	Adjective	Verb	Adverb
fishbowl	Yes	No	No	No
fish tank	Yes	No	No	No

As nouns, fish tank is a hypernym of fishbowl; that is, fish tank is a word with a broader meaning than fishbowl:

fishbowl: a transparent bowl in which small fish are kept
fish tank: a tank or pool or bowl filled with water for keeping live fish and underwater animals

Other hypernyms of fishbowl include aquarium, marine museum, bowl.

fishbowl (noun)	fish tank (noun)
a transparent bowl in which small fish are kept	a tank or pool or bowl filled with water for keeping live fish and underwater animals
a state of affairs in which you have no privacy