Who Gives A Fish Forums

We've had a pretty unusual experience with our guppy tank. We rescued three batches of newborns, totaling 19 babies, and they've all been raised in our nursery tank. Now that they're grown, it looks like every single one of them is female. What are the chances of this happening, or is there something specific that could cause this to occur?

I think it's worth noting that young guppies often appear female at first, and it's only as they mature that the males start to develop their distinctive colouring and fin extensions. Apparently, there are some telltale signs that can help you sex them earlier on, but I'm not entirely sure what they are - @Emeraldsea, would you be able to shed some light on this?

If you let nature take its course, it's entirely possible for a batch of offspring to be all female or all male, rather than a mix. @Snout is correct that young males initially resemble females before developing their male characteristics. Typically, the only distinguishing feature missing in young males is the gravid spot, which appears in females a couple of days after birth.

When pregnant females are kept at lower to moderate temperatures throughout their pregnancy, this can also result in more females being born. If you have a keen eye, you can determine the sex relatively early. I've created an illustration that might help with this.

Additionally, having a sufficient male population in your tank can actually influence the sex ratio of the offspring, favoring batches with only female fry.

kokomo wrote: ↑Sun Feb 06, 2022 1:00 pm Additionally, having a sufficient male population in your tank can actually influence the sex ratio of the offspring, favoring batches with only female fry.

It's worth noting that in the initial stages after mitosis, the default developmental path is always female.

All the theories about temperature, pH, and whatnot are interesting, but I think it's more about demographics. The species has a way of self-regulating, creating more of what it needs at the time.

I've seen it happen in my shrimp tank. Initially, all the males died off for some reason, leaving me with 7 females and one berried female. Almost all her babies are looking like males for now. It's statistically impossible for them to have been conceived in that tank, but somehow the species knew what the community required.

In a thriving, slightly overfed guppy tank, you'll notice that males and females come in waves. However, there will always be enough males to go around, so to speak. It's as if the species balances itself out to ensure the ladies have their pick of gentlemen.