yeah theres a way of doing it, i used to use and found it quite affective :
get a big sheet of black paper the size of your tank, then put it on the back of ur tank/s with a hole cut out, in that hole have a bulb, torch or light of some sought shining into the tank, as the fry swim past it, they can easily be identified, any fish without a little black spot above there anal fin is a male, any that do are females, the older they get the easier it is to identify. easy peasy
Shae 250