I am going to test my sexing method with a fillet knife in the coming weeks before my RES start to spawn. I will need to do this quickly as water temps have jumped into the lower 60's in the last week. Will the presence of eggs or the lack of be sufficient for determining male or female fish? Anything else I should or could look for? Any thoughts on minimum size to test? I am thinking 7" just to be safe but most RES should be sexually mature at 5-1/2". How many "samples" would folks like to see?
I have a fairly large year class of 7" RES so I can do more fillet sampling and confirmation of sex in the coming weeks. I can leave the "unhappy" fish pictures out of the posts if you like. Just curious if we have seen enough to make attempting to sex RES a little easier or if I should sacrifice a few more RES on the alter of knowledge.
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.
Cooler, muddy water is complicating my effort to come up with pairs for comparison. Tonight's result was just one fish, I will try for a male tomorrow night. I will spare you the "unhappy" fish pictures but the egg sack on this one looked quite a bit more mature and colorful than the previous female I posted.