Before you ask:

Yes, she is a beta spledens, so a "Siamese fighting fish", or, as they are known in Thailand, plakat. This translates to "biting fish".

Males are a "one to a tank" kind of affair. Females can be kept in groups, or "sororities".

Keeping them in jars/small tanks is cruel, and I do not support it.

It's not about the oxygen - they have a "labyrinth organ" to extract oxygen from air - it's about the nitrate cycle