I would say so, I would say that 80% of the time the urogenital opening also matches other characteristics that we would normally attribute as either male or female in RES. This difference is also easy to see outside of the spawn, go back and look at the pictures I took late last fall, the urogenital differences are still there and very noticeable. The larger the RES, the more noticeable it is.
Originally Posted By: sprkplug
Where does that leave the different colors on the opercular theory standing?
IMO RES have some sort weird dominance hierarchy going on that I have yet to figure out, I have watched it while feeding many times, it seems to become more prevalent as the spawn approaches. The most dominant fish tend to be the most brightly colored, both male and female, they also darken up more during spawning. In general females tend to be a noticeable shade lighter/duller than males, in general they also have thinner colored margins on the ear tab, but there is some overlap between dominant females and subordinate males. I do think that water clarity or the lack thereof also has an effect on how brightly colored the ear tab is. Keep in mind that I currently have just 7" of visibility now.
Every once in a while I do catch a smaller 4-1/2" to 5" RES where looking the urogenital opening leaves me scratching my head, I just assume that I have caught one that has not quite sexually matured yet.
