im sure no expert, but ive always doubted the validity of claims guppies are born a certain sex based on water temp. my reasoning being, i keep lots of guppies, and i do so in unheated tanks that year round average 68-72 degree's, and i get plenty of both sex fry. whenever ive seen folks comment on temps affecting sex with guppies its below 74, or above 74, well im always below 74, and get both. totally non scientific, but based on 25+ years of observation keeping guppies.