I just picked up a jag myself. Been reading a lot about them and from my understanding the best way to tell is by the stripes. I guess the females tend to lose their stripes once they get up in the 5-6 in range and the males stripes will stick around. Definitely looks like "he's" over that size but hard to tell from the picture. How big is the jag? should give a better understanding as to weather it's male/female. If it's over 6 in, I would go ahead and say it LOOKS male, but from my limited knowledge I can't say for sure. Just thought I'd chime in and give my thoughts based on what I have read. Curious though, what size tank is he in and do you have any tank mates with him? I have heard tank mates are hit and miss, just wondering what your situation is. I plan on putting mine in a 240g with a dempsey and an oscar. I know they are all very aggressive species and if it won't work out I will get rid of the jag, just waiting until he is big enough to introduce him to the tank before I decide if I will keep him or not. I think 240g should be enough space for them to live happily (hoping mines female)