A fishbowl is an object created by blowing molten glass into the proper shape with a glassblowing pipe. It requires a Crafting level of 42 to make, and gives 42.5 Crafting experience when made. Once made, players can fill it up with water, use seaweed on the filled bowl, and get Harry to put a tiny fish in it to get a pet fish (this is one of the tasks in Kandarin easy diaries). The bowl is also a drop from Mogres and Waterfiends.
Fishbowls are sometimes used to train Magic with the Lunar Spell Humidify, which fills any container in the player's inventory with water. Because the left-click option for a water filled fishbowl is to empty it, the spell can be cast at its maximum speed.