This is true they will change sex... however once they are female they will never go backwards... in other words, when they are young they are sexless, then the next step is male, then the last step is female, in that order but never the other direction. This is all determined by domiance, most dominate will be female, next dominate male, and if there is more in the tank, the rest will remain sexless until someone in the pecking order dies or is removed.
JMO