Is this a male or female?

Female betta's can be just as aggressive as male betta's, however looking at this paticular picture, the ventrals are relatively long and I don't see an egg spot so I would hazard a guess at it being a male.

I forgot to say in my earlier post, the only thing for me that makes me lean towards the possibility of it being a girl is the shape of the head, I find male's heads dip more than females do, and that is the only thing really that would sway me slightly