how big? you tried venting? that's the best way of finding out for sure and jgs are pretty easy to vent. nice jag you have there but I cant tell its sex even though I keep jags. vent it, best way!
It's looking at the small sex organ at the front of the anal fin. Unless you have done it many times...and been shown how by someone who knows how, it will still be a bit of a guessing game. Google it and you should find a page that give some pics. Trouble is, depending on the size of the fish they all look a little different.
Managauense isn't a problem. I've seen hundreds of them and it just gets easy to spot the sexes.
I am pretty sure this is a male I just wanted to make sure and get some other opinions. I had another Jaguar about ten years ago and it laid eggs on some of the rocks.