Hello; It has been over 40 years since I fooled with these fish but I will hazard a guess. bear in mind I may be very wrong or at least 50 % chance I am wrong. I use to go by the dorsal fin. Best I can recall if the dorsal fin ends in a point it is male. If more rounded then female. I think male. I know this is not universal and you should wait for others to chime in.