While the personlity, aggession and how passing any type of fish, including bettas will have a subtancially large effect in what type of fish that it can harmoniously co-exist with, typically male and female bettas don't work together and are known to fight to the death which is why your situation should only occur on accident, or during a breeding period as the majority if the time they will figh, and taking that .01 percentage chance can potencially kill, cause illness or stress your fish out to the extreme which In My Opinion, isnt worth in take the risk. Aggression towar other bettas concerning male/females situation usually occurs 1-2 weeks after introduction, as while they are just settling in they are already stressed and will sometimes show a minimal amount of aggresion towards the other fish but as they settle in and get used to their particular surroundings they will become aggresive and territorial, attacking other fish with similar characteristics such as other labyrinth fish, other bettas, colorful fish, long finned fish, large fish, and colorful top dwelling fish. Female/female Betta tanks can potentially work though. If they are planted heavily, with caves and decorations. You would need a minimum of around 5 females though.
Originally Posted by dramaqueen
Female Betta Sororities.
It is fairly well known that male betas cannot live together however, female bettas can live together under the right conditions. Here are a few things you need to consider before setting up a "sorority" tank, a community of female bettas.
Tank size- The tank you house your females in shouldn’t be any smaller than 10 gallons. 20 gallon long tanks work very well. A larger tank gives the girls more room to move around and also gives you room for plenty of plants, hiding/getaway places and decorations such as small terra cotta pots, bridges and castles. You can use either real or fake plants. The tank should be cycled, filtered and heated.
Number of females- Females can be as aggressive as males. The more females you have spreads out the aggression. It is not a good idea to have only two females together as this will cause one to beat up on the other and it could result in the death of one or both of the females. It is also not recommended to have less than 4 females. Six or more is better. Be careful not to overstock your tank.
Adding your females- Add the least aggressive females first. Two to three can be added at a time. Opinions differ on the size of the females. Some say that it’s best to house similarly sized betas in a sorority tank and others say it doesn’t make any difference.
Aggression- Some aggression is normal. There will be some nipping and chasing as they establish a pecking order. One female will become the “alpha” or dominant female. If you remove them for any reason, then rearrange the plants and décor, they will reestablish their territories. If a female is being overly aggressive and it doesn’t slow down after a few days, remove her. After a few days of “time out” you can try adding her back into the tank. If she continues her aggressive behavior toward the others, she will have to be put in her own tank.
Each female betta has her own personality and some will do well in a sorority setting and some will not. After adding your females to the tank, you’ll want to keep a close eye on them. You’ll want to do this when you are home so you can remove a problem female or remove and treat an injured one if needed.