With Jags, it can be quite difficult to sex them by the way they look. I've been tricked before, so I would suggest that you have a knowledgable person vent him if you want to be sure. As far as if you should get a male or female, I would recommend a female. One reason I say that is due to the size the males get and being that you already have other fish in the same tank. I have a pair of them in a 150g.