Join Date: Oct 2010
Location: Victoria, Australia
Vertical bars are a good indicator of readiness to spawn, but they are not the only indicator you should go by.
Usually when a female is ready to spawn she will respond very eagerly to the male's advances and show a lot of interest in getting out of wherever she is being contained and getting over to the nest.
There is often a certain way the female will move her body (I think people call it the s-curve) that can also signal that it is time to release.