Maturity and comfort really. If it feels threatened then she won't produce eggs. I know with some fish if you want them to lay eggs then do water changes regularly and raise the water temp by 2 degrees. It worked flawlessly for all my fish. Others just do it. My female managuense I used to have, literally as soon as she hit 4" she laid eggs. But at 4" they're sexually nature, and she was very happy in my aquarium.
Thanks heaps guys! So could someone tell me the ideal water temp to breed them in!? My tanks set to 28 degrees ! I deffenty can tell after a water change the males get huge humps and find a place and gard it!
Just raise the temp (whatever it is set at) by 2 degrees. Then wait a few days, and check the females stomach area before feeding. If she's getting bigger than normal then you might have some fry within the next week