Goldfish can survive a few years in a bowl because they are almost supernaturally hardy, capable of weathering conditions that would quickly kill most other fish. A bowl is a tiny, isolated environment starved of oxygen, which means even a slight change in the water chemistry can be lethal. I say this because goldfish pee with abandon. They unleash more ammonia than other aquarium fish, a toxin that would be diluted in a pond or a river but can kill a fish in a bowl.
