The one in the OP has more blue in its lower jaw than a typical male, and less than a typical female. We all know how to get a definitive answer - what's the point of a debate? Just net it out and take a look, and you'll know in 10 seconds.
http://www.fishhead.com/articles/ventsex.htm
I posted a "sex-my-JD" thread myself before and it got closed. No reason given. I'm not the one that thinks JDs are not worthy.