Bettas (I'm assuming your meaning domesticated Betta splendens) do not have a "natural" setting as they have been completely bred away from their original forms. They have been selectively bred for aggression and it is not a good idea to keep them in any size tank together except for the sole purpose of spawing, after which the pair is separated.
There are many other species of Bettas who can be kept together in pairs and even colonies and breed and live in the tank. If that is how you want to breed I suggest going with one of the wild species instead of trying to force domesticated B. splendens to go against the "nature" we have bred into them.
Oh, I know that lots of people here are going to think I'm an idiot or something, but here we go: Bettas are not supposed to be isolated as most people seems to think. Acctually, I think it is a sick way of keeping animals. Both my males and females loose their colors and get depressed when they get separeted from the others. I'm having around ten girls and four boys in a 50 gallon tank and there haven't been a single problem. They are almost always together at the same spot in the aquarium. And from time to time they spawn in the tank, but the frys won't survive, which is not strange since I'm having both tetras and barbs in the aquarium.
I'm sure that if you would have a big tank full of lots and lots of plants, and a couple of bettas ( say 2-3 males and about 5 females) you would be able to make them spawn in the aquarium, and if you are careful you should be able to get some frys to survive and grow up. I think it would be good to have for example lots of pistia stratiotes and java fern for the frys to hide in. Breeding bettas in this way would be a long-time projekt, and only the strongest, quickest, and smartest bettas would survive. But in due time I think the quality of those bettas would turn out pretty healthy, but maybe you should put in new bettas from time to time. I'm planning on doing something like this sometime in the future. I would probably use a 100 gallon tank, and let the plants grow for some year before I started to make my bettas breed, so that the frys would have lots of hiding places. Hopefully I will still have some boys or girls from the line I'm breeding now, and I would use maybe 5 boys and 10 girls or something like that.
OBS! Please don't be stupid and put several males that aren't used to other bettas in a small tank with no hiding places to prove me wrong or something.
So what? Breeders who have cultivated domesticated betta splendens for generations are wrong?
It has been proven, over and over again that this species of fish (and others BTW) actually do better when left alone. Unless you have proof of these fish living their full life spans (3-5+ years) your evidence is merely anecdotal. It would take years and hundreds of fish living to their full life spans to prove that domesticated splendens are happier in groups.
I am in the middle on this debate, I don't recommend that you keep this species male and female or multi males in small tanks together, however, in large tanks that are heavy planted so their of line of sight is blocked, it can be done provided that the Bettas are willing, not all males and females will co-exist, but some will and you will have better luck with related mixed sexes.
But as 1fish has stated-the big test is for how long they can be kept safely together.
I keep males and females together without issues, but I would not recommend this, my set-up are different than most, plus big tanks and Bettas related. I have not been able to keep multi male together even with my set ups for much longer than a year, males and females together is another thing.
I currently have mixed sexes together without issues for over 2 years in large heavy planted tanks (90-95% plants) not to say this could change any minute and they start to kill each other.
Thanks OldFishLady, thats some great insight to the situation. I am thinking about getting a 75 gallon tank tomorrow and filling it with wild plants I have got from the cottage. After cleaning them over a 3 week period I hoped to start a similar tank. My sorority plus some males, but I have heard the same. It deends on how well the males will do and how many plants.
I guess I will try it and do my best to monitor and watch them and see how they do.
I am starting a 75 gallon tank and cycling it for a month, but have this awesome black granite sand, and bright green plants found in southern ontario, hoping I can get it to a great natural state. Hoping also for your input. Thanks OFL.
Thanks again everyone, amazing feedback.
The thing with bettas is you NEVER know when they'll turn on each other. Like OFL said, one day they could be perfectly fine and than you look in the tank and see dead fish. They are VERY territorial fish. Unless you are an EXTREMELY experienced fish owner like OFL, I wouldn't recommend putting males and females together. You also would need to keep an extremely keen eye on them for a while to look for any signs of aggression, but like I said, even though they seem fine, they could end up attacking each other. No matter if they're in a "natural" state or not, they are still "fighting fish" and they are called that for a reason. You can't breed out their natural instincts like being very territorial. But like 1fish2fish said, there are other types of bettas that can live together.
#4 Even if it sounds disrespectful, I don't find it to hard to belive that generations of betta breeders have got it wrong. Especially since they were originally (can you say it like this? I'm from sweden and hope you'll understand me, even If I'm not to keen at the language) bred to be aggressive. And from my experiences bettas are more aggressive to other bettas if they are not used to social situations. For example, since I started to have my bettas together there haven't been much of torned fins and likewise when I try to spawn the bettas. Even if you breed and raise bettas to be aggressive, I don't think it takes to much to get them into their naturally behaviour. Maybe a generation or two in the worst cases, but I think that natural behaviour can't be bred away in only a few hundreds years, maybe not even in a thousands, though you can strongen or weaken most of them.
And I have to say that my bettas dosen't appear that territorial as people say. Ofcourse the males can get pretty aggressive when building their nest and rasing their frys, after alla, they aren't called fighting fish for nothing. And since I haven't been this intrested in breeding fishes and espcially bettas for a long time, and I'm not intitled to give you any scientific or long time answers yet, but I'm gonna keep you updated. And I don't understand why bettaxfishxcrazy thinks that they suddenly will turn on each other after showing no signs off aggression? First, there would be a reason for them to kill each other, they are actually animals. And second, why would they be all frendly, social and stabil one day, and the other day kill one of the others?
What I meant was if they feel like their territory was being threatened, they could start showing signs of aggression. They could feel safe and one day could feel threatened and they could act on it, whether it's fighting or killing the fish. There were multiple cases a couple months ago that people were saying they had acceptable fish in with bettas and they would be fine for months and than all of a sudden the owners saw the bettas attacking and killing the other fish. I love my fish as much as I do my dogs, so yes, I realize they are animals.
Hm, that sounds strange as my bettas are mostly swimming together, males and females. My males really doesn't seem to have their one territorys. The only time they get territorily is when the got a nest to watch. And may I ask you what your experiences are when it is about keeping betta males together? I don't mean to make it sound like you don't have any experience, I'm just wondering.