But Are you not sure or do you have a Short Finned Betta then there is still hope lets move on to the next way. Aggresion. Is one Betta being mean or really aggreive to the other babies(fry). This usually means you got yourself a boy. But just like people there can be some tuff chicks out there. So this way is not always reliable.
A female will always have a white dot on her belly this is where eggs are extracted from. Also male bettas USUALLY have longer fins not always but usaully. But this is after they are full grown not when they are still fry. If you are still unsure you might want to put it into it's own tank and watch it grow and see what happens.
