It is still a little early, late May or early June is probably the best time to try to sex RES. I am pretty sure the big RES in my aquarium is male but it should become more obvious as the days get longer. I'm guessing close to 9" now, was 4"+ last June when I seined it out of the pond. My best guess is that three of the four I have indoors at the moment are male RES.
