Betta Splendens, also known as Siamese fighting fish, are often found in offices, stores, and homes in non-aquarium conditions: no heater and no filter. They are also often in very confined places by themselves. If you do choose to keep a betta fish you may keep them in a standard aquarium, just beware that their long fins are very tempting for other fish to nip at. However, the majority of them are kept for "decoration" in bowls or vases. If you do intend to keep bettas in that way please try to follow these key points:
Choose a well lit and warm location: Due to the lack of a dedicated light and heater, you should put the container in a spot that will get a healthy cycle of day/night light and be temperature controlled.
Use at least a half gallon of water: Some designer containers are increadably small. Remember that the fish respiration and waste will be expelled in the water and accumulate until the water is changed.
Use real aquarium gravel: The beneficial bacteria colonize best on real aquarium gravel rather than the marbles that some manufactures want you to use.
Put in a plastic plant: The fish need a hiding place to turn to when they want to get away. Adding in a plastic plant will do wonders to stress relief. Also, algae will accumulate on the plastic plant, this will help since algae eats ammonia and nitrate.
Do not overfeed: Overfeeding should always be avoided, but since there is no mechanical filtration you must not put any extra debris in the water that will add to the rate of pollution. Feed it once a day and only what it will consume in 2 to 3 minutes.
Do water changes once a week: Since there is no filter you must change the water more frequently than you would otherwise. First, remove the plant and stir up the gravel to get the settled waste to float, then pour out 90% of the water (careful not to pour out the fish). Second, wipe any algae off from the inside of the container. Third, add in aged water to fill the bowl. Four, start aging enough water for next week.