I think I have to follow up (sorry for the late reply...I just found the thread). My BN is just showing his sex IMO based on what I've read because his "bristles" on his face are starting to fork and just in the last week have really developed. This, I've read, is a sign of him being a male. Until now I thought it was a female.
Besides the bristles, I have no way of knowing what sex it is...I've never sexed any fish unless they are clearly pregnant, in which case I know they are female : )
Mine is about 3 inches long now and starting to show some nice bristles on his face. I don't know how old he is - I just bought him. He was the only one in the tank with bristles in the tank so I assume he was the only male.
I stupidly assumed these would be long finned since they had a big beautiful display of adult long finned BN's. How soon can you tell if they will be long finned or not?