The best method to know if your fish is going to give birth soon is not to judge if she's "fat" or "squared off" because not everyone can tell and definitely not every fish looks the same. I think the best method is look for the changing behavior of the female. In this video I talk about how within the week that the female is going to give birth, she will start to swim alone and hide from the other fish. This is probably a motherly instincts to protect her young despite the fact that some eat their own offspring.
Hope this video helps and thank you for watching!
