At this point in my fish education and experience with RES, I would not try to sex RES outside of the main spawning period - way too risky.
I agree Bill.
I will say that the width of the orange/red margin on the the ear tab might be the best indicator of sex even with immature fish. Wide colored margins male, very thin margins female. The only problem using this is that you may occasionally get a male with a thinner than average colored margin, and female with a wider than average margin, or even individuals that fall in between the two.
I started this thread in order to try and sex the five RES I overwintered earlier this year and the width of the colored margin on the ear tab ended up being more accurate than going by any other visible trait.
I will take more pictures of the fish I catch and try and remember to include pictures of the vent as well.
