Shorty, Your work is outstanding! If you could post more side by side (or in this case, top over bottom) pictures of similar sized male and females like you did that would help. You mention the difference in the urogenital opening pore size. But if we have side profiles side by side and we study 5 or so examples, we may find other characteristics that also readily will help confirm from the outside. Perhaps if we can find 2-3 appearance characteristics that are reliable we won't have to cut them open in the future.
So far we know that the degree of redness on the ear flap is not reliable. The urogenital pore seems fairly reliable. But there must be other physical features. It just takes some examples and then some pattern recognition to find them.
For example, you can't see the fins well in these examples but would the male and female have the same number of rays in all the fins if compares side by side?
Or, in the example above, the male fish at the top has a funny looking scale pattern just north and a bit east of the ear flap. If the flap as a circle was a clock, just past 1 pm there is some unique markings. The male has a slight depression and then a concavity shaped in the shape of a triangle or 'less-than sign' In that same area the female has 2 discrete rounded mounds in a stair step pattern. That may just be random scale difference but if we lined up 5 or 6 pairs of fish, about the same age, length and male right next to female, we might catch more patterns.
