There are many beliefs on this topic.
1. Such as the sex will be more to the younger sex - more males if male is young, more females if females is young.
2. Temp. plays a role on sex outcomes - lower temps will produce more females.
3. The first three spawn (female) will produce more males, thus female will be culled after her third spawn.
I rely on belief 2 and 3. A first spawn during the hot season may produce 90% males (my highest). 2nd and 3rd spawn during hot season may produce 40-60% males. 4th spawn during hot season = below 30% male.
2nd and 3rd spawn during cold season may produce 60-90% females (I have 3 spawns like this). 4th and more spawn during cold season = 90% females.
I'm still waiting for a first time spawn during cold season to grow. Will have results next month or so - if they survive.