11-15-2011, 02:22 PM
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I cannot see the ovipositor (breeding tube) in the photos, and that is the most reliable way of determining sex in these fish. The first rays of the dorsal are longer in the upper fish, suggesting a male, while the lower fish may be female. And there is a slight pinkish-hue to the lower, also suggestive of female.
Assuming they are in the same aquarium, careful observations of how they interact would probably be the best method. Males will continually challenge each other if they are within sight of each other. Assuming the upper fish is a male, if he allows the other to be near him without any "pushing" away, you probably have male/female.
Males do not always accept any female. They form a bonded pair. I'm not saying that this male won't accept this female (if that is what they are). We can't second-guess the mind of a fish.