Male & female JD look pretty much the same but with 1 difference. Fin shape..

That is a female JD

Females have rounded fins & the males come to a point that stretch to the tips of their tails (it the back fin & the butt fin I'm talking about).

I had a JD for about 5-6yrs.


I think I saw other fish in the tank.. You do understand he will kill them right? Hes an agressive fish & will require a min of a 50gal tank. A lot of fish stores never stay those parts & they can grow larger then 8"

Here is a small wiki on the JD Clicky



EDIT:

How much are you feeding her??
If you over feed the fish will create too much amonia & that could cause the fish to get HITH (Hole In The Head). Its common in large Cichlids. When you see all those large Cichlids with ugly pitted faces, thats caused by HITH. & it'll kill the fish over time. So as a young JD a small feeding/day.. When fully grown 1 decent feeding every 3 days. It helps to prevent HITH & so the fish wont get fat & unhealthy either