We have all been to the home of someone who has a small bowl or vase containing a magnificently-finned and beautifully-colored betta fish. Perhaps there is a plant in the bowl, and some colorful gravel, and the fish seems to be just fine. So you may think the question is foolish.
The answer to the question is yes, you may keep your betta in a bowl or vase, but I can assure you, he will be much happier (and healthier) in a larger tank. Perhaps you've heard the story of how betta fish can live in shallow rice paddies. This may be true, but remember that while it may be shallow, a rice paddy also covers a huge area, so the fish have lots of room to swim. While a betta fish is not a particularly large fish in terms of its actual body size, with their elaborate, showy fins and tails they need more room than you might think, especially if you put plants or other decorative items in their tanks.
For one male betta, I would recommend a minimum tank size of five gallons; ten gallons would be even better. And you may have heard this before, but I will repeat it: NEVER put more than one male betta in a tank. They are called "Fighting Fish" for a good reason! They are extremely territorial and aggressive.
You may give your betta some compatible tank mates if you wish, but keep in mind the more creatures you add, the bigger the tank must be. While you may indeed mingle other fish and creatures with your betta, choose them carefully. Do not add any other brightly colored fish or fish with flashy fins, as your betta may react to them the same as he would to another betta. Also, because bettas are tropical fish, do not mingle them with cold water fish, such as goldfish. Some suggested tank mates are snails, ghost shrimp, Neon Tetras, Otocinclus and Corydoras.
If you are planning on keeping female bettas, I recommend you keep a minimum of five or six of them in a ten gallon tank. They can be aggressive as well, but on a different level. They develop a certain "pecking order" and with at least five of them, the aggression will be less targeted on any one fish. Be sure to keep some plants and perhaps a small hollow "house" in the tank so the less aggressive females have a place to hide from the more aggressive ones.
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