The one thing I hate the most is trying to sex a jag before sexual maturity.I cant tell you how many times I was way off.you can literally go crazy from staring at the tank all day and flip flopping between male and female they change colors every 5 minutes according to mood,but at 5-6 inches if its a male you should know his body will be torpedo shaped and his colors will come out and be very vibrant with jaguar like patterns and purple sheening..also even easier way if you dont know how to vent..go out and buy 3-4 more and let them form a pair ,then you will know who is male or female.