What fish can live with a Betta fish?
Male and female Bettas are peaceful fish and can live separately
in a community tank with other fish. However,the males should not
be placed with fish that have long showy fins like angels. Females
can only be introduced for breeding then should be moved to another
tank. They love to swim so please don't force them to live in a
Female betas can live fine with other fish. Sometimes they can be aggressive with other females but that is not that common, especially if in a large tank.
Mixing a male with female there can be some aggression when the male is interested in the female, this can lead to breeding (which can result in you having up to 500 betta fish to separate and care for!). Make sure there is plenty of room and hiding places so that the female can escape male advances. Betas prefer calm water, though I have placed in tanks with slow water circulation and with several areas with very little circulation allowing them to be comfortable and not stressed.
Long story short: If tank has fish that do not have long fins, that there is plenty of room/space, and water that is not too swift, betas should thrive fine.
Well, if you love your Betta fish, then it should live by itself. But if you add another Betta to your current Betta fish's tank, then they will start a fight because Betta Fish are Siamese fighting fish and if one Betta is in contact of another Betta, the possible reason would be a fight between them two.