FEMALES. Females usually have shorter fins, but I've seen some with really long fins and they are usually less beautiful or dull, but they can have excellent color. So the easiest way to tell is to look for an "ova" or ovipositor, this is where the eggs come out of the female during breeding. It looks like a little white pimple located behind the vendral fins (the 2 little ones that hang down in front). If it has an ova then you've got a girl. (picture lower left)
MALES. Males usually have long beautiful fins, but there are some types of wild betta that the males have short fins. So just make sure it doesn't have an ova.
Basically the main difference between boys and girls is the ovipositor.
