Hello. If you only have the one fish, it's going to be very difficult, if not impossible to determine gender. That's because body shape is one of the only ways we have to judge it and without others to compare it to, you are pretty much out of luck. The females can be easier to spot, in a group because the belly on a mature female will look more plump, compared to the males who are much more streamlined. The males have been described as looking like a torpedo. At breeding time, the females get noticeably fatter while the males will grow breeding tubercules. When males are ready for spawning, they develop the tuberdes on the head and pectoral fins, principally along the bones of the fin rays. They will look like small raised spots and are sometimes mistaken for white spot disease. (Ichthyophthirius). If you do only have the one fish, it might be good to visit someplace that has several and have a knowledgeable person point out some examples of both sexes, then you may be able to make a comparision with your own fish. I hope this will help. If you need anything else, let us know. Patricia