Well?
Suppose we don’t know the gender.
Also, if they do fight, is that unethical? 
I have Beta’s. The males will fight each other. (watch their gills swell)
To watch the gills swell, wait until the Beta comes to the front/side of the tank and put your finger on the glass in front of him where he can see it.
Females will tolerate each other.
Hmmm…any surefire way to determine the gender?
Describe the gill swelling in more detail.
Betta splendens, the “Siamese Fighting Fish”?
Two males will do their best to destroy each other. Lock onto their opponent with bulldog tenacity. Shred the flowing fins. They will even make nasty faces at a mirror.
In the wild, the ancestors of the domestic betta lived in small pools, each of which was only large enough for one male and his nest. The territorial inperative became very strong, and when the fish were specially bred this aggression was selected for, as well as ornate fins.
Females are far more sociable.
Here’s a site with more links about bettas than you can shake a tubifex worm at:
Males are the colorful, pretty, flowing-finned fish you usually see in those itty bitty cruel cups in the pet stores. Females are usually duller colored and short finned. Although now I think they’re breeding the females with brighter colors. The males will fight if put together, the females usually don’t fight.
They’re not cruel. Bettas don’t particularly like wide spaces, and aren’t fond of moving around a lot. Given a small space they are quite happy to just sit in it. In my experience a betta given too large a tank will become stressed and unhealthy.
Zhao: I’ve seen them fight. The males absolutely will fight given the opportunity, and can cause serious injuries. they tend to just go for the fins, but can take off scales and fins at the roots, opening the fish up to infection. They shouldn’t be exposed to that danger.
Goodness, how timely.
Mother decided that my daughter’s betta was lonely, and bought him a mate today. We put them together in the vase and the male hasn’t stopped chasing her yet. He has yet to catch her though. We added a couple of plastic plants to the vase to give her someplace to hide.
So is there any hope for her? Or should we anticipate waking up once more in a single fish household?
I’ve had bettas going on 10 years now. It is possible to keep a male and a female together. However, having two or more females in with the male is ideal. If the male is outnumbered he won’t be as aggressive. Having a 10 gallon tank or larger also cuts down on aggression. Having them both in a vase puts them in too close proximity to each other. Bettas can also be kept with other community fish (I used to have a betta with 5 blue moon platties, and they never fought), but if you do this make sure that you ask the aquarium store which fish are compatible with bettas. If you get “pickers” like guppies, you might wind up with a finless betta.
The betas may fight, but the VHS wins.
A Laotian friend once told me that when she was a child capturing and fighting Bettas was as common as kids playing marbles or baseball cards once was here in the states. Her brother won enough betting with his champion males to buy a several Beatles albums (very high status items; her family was one of the few with electricity in their village).
You have to be really careful – sometimes a male and a female (or two) will get along, sometimes they won’t. More often females do, but sometimes they don’t either. These are fish with Attitudes.
And the cups at the pet stores ARE sometimes cruelly small, as are the bowls they always seem to be selling for bettas. My guy is in a 2 1/2 gallon aquarium and is happy as a clam. I wouldn’t keep a betta in anything less than a gallon, because they do need some swimming space and more importantly – water changes. Can’t cycle a one-gallon bowl, so you have changes, and too many changes stress the fish. I strongly recommend avoiding the tiny bowls unless it’s a temporary accomodation during water changes.
I agree with whiterabbit, Betta can survive in small bowls (then don’t need airstones because they can breathe normal air) but in my experience bigger is better.
My first betta lived a very happy life in a 20 gal hex tank alone. He also didn’t tolerate any other fish (I threw in a few Guppies and he would chase them continuously).
IMO a hex 2.5 gal is probably the best for a single betta.
Dude, just because they CAN survive in those little tiny cups doesn’t mean they’re content. They at least need a gallon or so to stretch their fins. They’re FISH. They need to swim. here , here , here , and here
Most bettas I see for sale at pet stores are Betta Splendens. These are fish that are about as far from wild, rice paddy living fish, as one can get. They’ve been bred for longer fins and bright colors, and there’s small likelihood a breeder is keeping them in stagnant pools on the back forty.
Most fish are kept in the distrubtor’s tanks by species, shipped in the bag by species, and then placed in the pet stores’ tanks grouped the same way. Not only will bettas fight if they weren’t kept in cups, they would very likely be stressed by the more active fish, and nipped to tatters by the other fish as well. The cups are for storage and shipping, not housing.
If you look at shots of breeding labyrinth fish and other anabantoids, the water is not necessarily deep (in the wild or captivity), but it is heavily planted and is either changed often, or has a large reservoir of water to draw on.
Some advantages to having a larger tank besides the ability to have it heavily planted, is a longer time for the water quality to decline (more room for plants, the bacteria to break down from left over food, etc.), a larger tank is more forgiving with beginners (since bettas are often sold as a beginner’s fish), usually comes with a well-fitting lid (bettas like to jump), easier to create hide spots if a betta is not going to be kept singly, allows room for better filtration and lighting.
This last bit to me, is common sense: It doesn’t matter what the pet store or a friend says you can do, and still keep the fish alive. Look at what the fish enjoyed in its native environment, or in optimum conditions by a breeder, and try to mimic that as closely as possible. Granted it’s just a fish, but you went to the trouble to spend the money and choose the fish, so why not do the most you can do to keep it as a pet, rather than the minimum?
I believe the OP has been answered, but will add, I don’t believe even the best breeder can predict whether two bettas (of opposite sex) will get along. He can watch for the signs that the male is ready to breed and try introducing a female or more than one and see what happens. If the conditions are right and the breeder provides all the right incentives, the likelihood of success is greater, but the rest is up to the individual fish. I’ve kept a male betta with three females and had minimal problems. I also had a male that consistently harried the other females in his tank and created a generally stressful environment, but did fine with other fish in a community tank. I don’t think there is any one foolproof formula.
If you want to see a betta flare his fins…hang a mirror outside the glass off the tank or bowl.
They will flare every time they see their reflection.
My guy doesn’t flare at mirrors – most do, but occasionally one doesn’t. Silly fish.
They aren’t difficult fish, from what I understand, but they do take some work.
If you put Release Candidate 0.7.5.1 Build 393 in the same tank with Build 374, look out!