I think that they will fight. Well, if the divider is clear, like glass, then they will fight. Betta fish are also called Siamese Fighting Fish, and will attack the same gender. If the divider is dark and you can't see through the other side then I think they will be fine and not hurt themselves slamming into glass. If you want to have fun with them, put a mirror on the tank and watch them slam into the wall. Don't do that too long, or they can get hurt. I hope I helped!
None are recommended if the Betta is a male.
No. Betta fish will attack each other no matter the sex.
keeping multiple bettas in the same tank is not reccomended
Male Betta splendens fight with other male Betta splendens so the answer is most other fish will not fight with a Betta in the same tank. To try to list every species of fish here would be impossible.
Any.
No, because they are fighting fish and one of them will kill the other.
You should not put your Betta fish in the same tank in the first place, most likely the male will kill your other fish. by res do you mean red eared slider?
Female Betta fish can be fairly good community style fish and should be fine. Male Bettas would massacre the community.
beta fish are very territorial if there is plenty of room for both of them in a tank they will just leave each other alone and another reason is that they haven't had to compete for food
A male beta fish blows a lot of bubbles. so if there are a ton of bubbles at the top of the bowl or tank, your fish is most likely a boy.
Female beta fish are better in this way, they don't fight, allowing you to put them in a tank with each other as well other fish!
It's best to only put male and female betta fish in the same tank/bowl if you are breeding them. If they are not breeding and they still stay in the same area, the male would most likely attack the female, so keep the female away! Also, if you are breeding betta fish, make sure to remove the female betta after she lays her eggs, as the male will care for them and chase the female away.