Betta fish (or commonly known as Siamese fighter fish) will flare when they feel threatened by another Betta, even their own reflection.
Male Betta fish cannot be homed in the same tank as they will fight to the death. They also cannot be housed with female Betta fish, they are only allowed in the tank to allow time to reproduce.
Female Betta fish are allowed to be housed in the same tank. A group of them is called a sorority.
Flaring is a good way for your Betta to get out any tension or frustration in their body. Ideally you will allow your Betta to flare for a maximum of 5 minutes each day, if not then at least once a week. If you allow them to flare for more than 5 minutes then it can cause them a lot of stress and cause them to nip at their own fins.
