I read somewhere that the females are smaller and have golden scales on their belly. With my pair, the larger is about 3 1/2'' with only slight coloration other than the black & white stripes. The other is half that size w/ a golden belly & some beautiful turquoise coloration on the fins. The thing that confuses me is that when they mate, I notice the eggs on the cave wall & it looks like the smaller one is fertilizing them. As far as trying to tell by behavior, they are constantly breeding so they are both very defensive/aggressive. I confused!