Originally Posted by lixx
I see. That makes sense. I was trying to figure out why they couldn't be in larger tanks. Do the females get along with most other types of docile fish? How can you be sure you get a female, other then the sellers word?
Females and males can get along just fine with other docile fish, but males may have problems with things like guppies. Their long tails may confuse a male Betta into thinking the guppy is a rival. Problems will arise then.
Females and males are very obviously different, once past a certain age. At around 2-3 months of age, the males' fins begin to grow significantly longer than their female siblings. Once mature, all males have much longer fins than the females.
I had an interesting thing happen once. I bought a female and brought her home, and proceded to put her next to one of my males. She flared, and slammed against the side of the tank, and tried to get to him to kill him. Meanwhile, he kept looking at her like, "Are you nuts?!" I did a small experiment with this new female. Moved her next to my females and she showed off for them. Next to males, she tried to kill them. I studied her more closely and realized, this was no female. This was a very young male.
Had I paid closer attention, I would have noticed his fins were a tiny bit longer than all of the females in the community tank he came from. However, he even fooled the breeder, that or the pet store. (My LPS claims he came marked as female, but who knows.)
I took HIM back, because I didn't want another male at that time. They put him back in with the females and said they would watch him. He vanished the next day and I have a sinking suspicion they refused to believe my observations, and sold him out as a female again.
So, every now and again you may not get what you were expecting, but as long as the Bettas are above a certain age, it's pretty easy to tell what they are, so you can take the breeder's word on it.