All-female guppy babies?

Is this possible? We rescued three different batches of newborn guppies from our guppy tank for a total of 19 babies. They have grown up in our nursery tank and ALL appear to be females. What could cause this, or what are the odds of this happening?

All young guppies look female. They develop male characteristics of colour and fin extensions after a few months. There are allegedly ways to tell earlier, maybe @emeraldking could explain?

Well, if you let nature take its course, an all female or all male offspring in one batch is something that can happen instead of a mixed sex offspring.
What @Naughts is saying is that young males look like females before they show their male traits. That's normal. The only thing that is missing in young males is the gravid spot that will be shown after a couple of days after birth in females.

When the pregnant females are kept at lower till moderate temperatures during the whole pregnancy, also more females will be born.
If you got a good eye, the sex can already be determined pretty early. Try this illustration, I've made:

Also If the population of males is high enough in your tank, it can promote batches of females only frys.

MaloK said:

Also If the population of males is high enough in your tank, it can promote batches of females only frys.

Click to expand...

Which is easy for the first embryonic state after the full mitosis is done, is always female.

I heard all the theories about temperature PH etc...

It's based on demographics, the species will always magically create more of what it statically needs.

I can see it on my shrimp tank that I started. At some point in the beginning all the males died. for a X reason... I was left with 7 females and one of them was berried. nearly all the babies she had are looking like males for the moment. It's absolutely impossible that they have been conceived in this tank, but "it" knew what the community needs.

In a free for all slightly overfed Guppy tank. Males and Females will come in waves. But there will always be enough boys for all the ladies to crush on.