Also, most fish require something the Betta doesnt- airation. Bettas and a few other fish, like goldfish, have a gland (Larynth gland I believe) that allows them to take air from the surface instead of through the water, so filtration and circulation would be required over a Betta. HTH.
Bettas and other labyrinth fish, have an organ called the labyrinth that allows them to breathe atmospheric air, goldfish do NOT have the labyrinth organ. Goldfish should not be kept it bowls. It's already illegal to do so in Rome.