noun
goldfish bowl
A bowl-shaped container for keeping goldfish, typically made of glass.
金魚鉢の水を替えた。
I changed the water in the goldfish bowl.
水槽 is a general water tank or aquarium, often larger and for various aquatic life, while 金魚鉢 specifically refers to a bowl for goldfish.
Compound of 金魚 (goldfish) and 鉢 (bowl).