In an ideal spawning, 100 fish would distribute evenly betwen the two sexes, but so often this ratio can be skewed, and entire species have been lost in captivity because of this- I'm looking at you Roloffia monrovia. In live bearing tooth carps Joanne Norton showed that pH and temperature affect sesx determination but in the killifish that are egg laying tooth carps these mechanisms do not work and we have no idea what causes skewed sex ratios in killies.
Here are papers related to that area of research.
Sir Paul Nurse - Great Ideas of Biology
This is an long talk by Nobel prize winner Sir Paul Nurse, who has a rather Monty Pythonesque delivery style of explaining concepts to the lay person. He explains great moments in biology - the cell, evolution, the gene and biological complexity in terms anyone can understand. After watching this you'll have a much greater understanding of how and why things work the way they do
https://www.youtube.com/watch?v=WasSyu9slpk
