Is My Betta A Boy or a Girl?
If you have bought young betta fish, you may not be entirely sure whether or not they are male or female. Sometimes pet stores claim that fish with short fins are females, whilst fish with long fins are males. Whilst this is often true for mature fish, it is by no means always true, and if your fish are young, then it may be completely inaccurate.
The fact of the matter is, some Bettas delight in confusing their owners with their gender antics. One moment it seems you have a male fighter, then next, no, probably a female. There are a variety of signs which point to what gender a fish is, and I will outline them here.
Generally a male, short fins, generally
a female. However there are some longer finned females out there. If
you look at the ventral fins (the first pair of slim fins under the
fish,) males tend to have longer fins than females, even if they are
overall shorter finned fish. In the wild, Betta males don't tend to
have the huge fins you'll see on captive bred Bettas, so quite often
throwbacks to the wild type occur and males will have shorter fins. This fin type is known as 'plakat.'
Males are usually more colorful than females. This is a sign you have a male fish, but it is not the be all and end all. There are plenty of brightly colored females out there as well. However, when combined with other traits, this can help determine the gender of your fish.
The ovipositor is a white bump on the underside of the fish just between or slightly behind the ventral fins. This is where the female will lay her eggs from, and this is usually a 99.99% telltale sign that you have a female on your hands. Some males occasionally seem to have a little white dot in the same place, but are still males. This is relatively rare, however.
Male fighting fish and female fighting fish can both be aggressive at times and they can both flare their fins, but males make a much bigger display and also puff up around their faces in what Betta keepers call a 'beard'. If you have several fish and you think you have a male among them, try separating him from the others but keeping him in the tank, or giving him a mirror to look at. If he gets all angry and flares up beard included, you have yourself a boy. It's not a good idea to let Bettas flare all the time, so make sure you provide privacy for him once you work out what gender he is.