Swordtail fry always all female

[Spider8ait1994]

Yeah I’ve had the same experience. I have all my fry in a seperate tank to the adults to raise with the oldest batch being almost 3 months old and the youngest batch being about one and a half months.
They all seem to be female at this stages I’ve been wondering the same thing whether tank conditions could play a part in what sex they turn out.
I’m not concerned either way what sex my fry end up I’m just happy to get the experience of raising them.

 

[twentyleagues]

Like duanes and others have said there are many reasons it could happen. Water parameters are a big one pH, hardness, nitrate, can affect growth and sex.

Another theory is that fish excret hormones that affect the development of other fish in their area. It's not far fetched to think males may have a hormone that affects sex of the offspring in it's area so that that male stays the dominant male as long as possible.

I also think it may be that they just haven't shown as male yet.

I know some species of fish can switch gender. Clown fish are all born male and the most dominant one becomes female. I've bred clowns in the past. I didn't know any fish could freely switch gender back and forth though. Seems that would take a lot of " energy" and would only be used in a "last ditch" effort of survival if it is a thing.

 

[Toiletcar]

My Rio Otapa helleri always turn male eventually. Mostly when they get really large (4-6”). When they get that old they turn male but can’t breed. These large males don’t get aggressive w/ younger males that are constantly fighting and trying to breed.
Another weird fact about swordtails is females can store sperm from males and give birth later on. Also the black gavid spot is actually the eyes of the young. They really are interesting little fish.

 

[duanes]

These are X mayae, a continuing source of dithers for my cichlid tanks.
And mine always appeared female for an extended period.

As soon as an adult female would appear gravid, she'd be moved to a separate grow out tank to give birth

You may want to try moving fry to separate tanks, and amp up your water change schedule, to remove hormones to see if it effects sex ratio.
The hormone theory twentyleagues proposed is another definite possibility, and the only way to remove them, is with frequent water changes.
Same goes for growth stunting hormones that alpha fish often emit.

 

[phreeflow]

I don’t mess with swordtails anymore for this reason. Weird fish…will buy a group of large swordtails with obvious dimorphism and some “females” will inevitably turn into a giant male with a stubby sword.

Currently have a sizable group of cauliflower females with some red eye albino males and they have NEVER gotten gravid. They’re not like I used to remember them as a kid. They were easy then. Even guppies are hard as hell to keep nowadays