So, more and more I have seen people attempting to keep Bettas together, which can be seen as incorrect or dangerous. I feel we need to be able to educate everyone, on the pros and cons of keeping Bettas together.
Each Betta is different. Some can be kept in a passive community tank, or in a sorority, however, there are some who are most happy being in their own tank without tank mates. Know your Betta, know THEIR needs.
Male Betta and Male Betta:
Though it has been done,
it is not for everyone.
It is most recommended to keep all males separated, to avoid injuries and death. Injuries can lead to infections, which is not what you want to deal with. If you feel the urge to get another Betta (as we all have), make sure to be ready.
Either have a tank on hand already, or buy a tank while buying the fish. Remember these fellas need heaters!
I have heard of some people having males together - often siblings - however they have larger tanks, often long VS regular or tall, and those tanks are cycled, planted, and have natural sight dividers such as driftwood, or taller plants. These tanks are set up much like a larger sorority tank, but can be more difficult.
If you are keeping males together undivided, expect fighting, showing off, torn fins, and in extreme cases severe injury, lethargy, and death. When the immune system crashes problems such as Ich and Columnaris can hit. Then that means you need to medicate TWO fish. Is it worth it?
Male Betta and Male Betta DIVIDED:
This is a pretty common way of using one tank for more than one Betta. Dividing a tank is the safe route, as long as you still provide enough cover for them. Some males will still become stressed, which can be seen in their behaviour, or even physically. Example: Tail biting, or lethargy.
At first the males will flare a lot at each other, then eventually flare to communicate, or completely ignore each other. Make sure to keep up with your weekly water changes!
Make sure to also keep the water level lower (3 inches or so) to avoid one of them jumping over the divider. This can become more dangerous since it is now half the space, and they will probably be right up in each other's face. Expect torn fins, or even injury. Worst case scenario: Death.
Female Betta and Male Betta:
This is another method most unrecommended, especially to new hobbyists. Betta fish emit a scent, as if to say "Hello! This is me!". Males and females both have different scents, due to gender, which makes their presence known.
Keeping them together in an undivided tank can cause some problems. They may breed, they may not. This can cause stress on one or the other, or both.
The female may become:
lethargic, sick, egg bound. She may also clamp up and hide, or become the dominant one and harass your male.
The male may become:
Stressed, frustrated, lethargic. He may also show these signs through tail biting, clamping up, or become more violent than you have ever seen your seemingly passive male.
Such cases can cause illness and death.
If this method is attempted, a large tank is recommended - once again preferably long VS regular or tall. Stuffing the tank full of live and silk/fabric plants, and tons of hiding spots would be recommended. A heated cycled tank, plus proper husbandry, can make it possible for the fish to live in peace. Please remember every Betta is different. Not all will accept this odd change.
Also let it be known, if they breed... The male will keep his nest safe by fending off the female. This may include KILLING her.
Female Betta and Male Betta DIVIDED:
Dividing a tank ensures the safety of both your fish. Though the scent of both genders is still present, they are at least safe. If you can, have the tank cycled (filter required) to help. Proper husbandry will also be a must. Have enough coverage and hiding spots, so that they do not see each other all the time.
The female can still become stressed, and the male as well. Not all Bettas are okay with this particular set up. Know your Betta!
Also remember to keep the water 3 or so inches below the divider line.
Female Betta and Female Betta:
Keeping two females together is not okay. For females, they need to establish a hierarchy. If there is only two, there leaves one as alpha and the other as the weaker female. To even out aggression and avoid illness, injury or death, it is recommended to have 4+ females together in a tank that is stuffed with live, silk and fabric plants plus hiding spots. 10 gallon is the smallest tank recommended, plus having the tank cycled can help you out a lot. Proper husbandry is still needed (as it is with any fish, any set up). Some females will be very very aggressive... And may not be able to live in a sorority. If that happens, make sure to have a back up ready.
Make sure to quarantine all new fish for 2 weeks.
If you introduce a seemingly healthy female, who has for example... Columnaris... Now your whole tank has it, everyone has to be quarantined, and you run the risk of losing your whole sorority.
If you have a pretty barren tank with females, you run the risk of lethargy, illness, injuries and death. I've seen female Bettas gang up on another female. Having enough cover, ensures your tank can remain peaceful, and healthy.
Male Betta and Female Sorority:
I have noticed that recently this has been another common set up. It is still not recommended especially for new hobbyists.
The tank must be big enough to support the male with the females. The more room, the better. The tank should already be set up for a sorority (very dense, cycled, heated, etc). If adding the females after the male or vice versa, removing the fish rearranging decor and doing a partial water change is recommended.
This way there is no "territory" that has been claimed. You could also try leaving the fish in, rearranging decor and doing a water change. However, better safe than sorry!
Problems that can occur:
The females gang up on the male, the male kills or severely injures the females, they become lethargic, stressed, clamped, and more prone to illness. Not all males can be in this set up.
I have noticed it is recommended to keep older male giants in a sorority, to keep them active since they are more prone to illnesses as they are lazy when they are older. Just remember: MORE space is BETTER.
All in all, males prefer isolation while females can be together if the tank is set up properly. I personally will never recommended most risky set ups, but I know that it can be done. RESEARCH. RESEARCH. RESEARCH. I cannot stress enough how dangerous it is to toss two Bettas together and "think" they care for each other. The male does NOT need a "girlfriend".
Do not, under any circumstance, put your wants and feelings before the fish's needs. NEED overpowers WANT
. It is up to you to care for them properly.