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I've been doing some pondering, and one of the questions that has sprung to mind of late is this: do any livebearers change sex?

I know that there *are* fishes that do this, but I was wondering if this happened among Poeciliid fishes. I don't think any do, but I just thought I'd check and make sure in the light of some recent confusion when researching a different topic.


Panda Catfish fan and keeper/breeder since Christmas 2002

Well Calilasseia I can't be sure but I swear that this did happen once with some swordtail fry that I raised. I had 8 fry three of which I could tell were males after around 4 months. The other 5 were all females or so I thought. It was moths and months later and when they were almost fully grown that I noticed one of the females was starting to developed a point on the tail well I kept looking at her anal fin but it was still the shape of a females but gradually it changed its shape and became the male shape. All the other males are still very small compared to this one. This one is very big it is the same size as the females but he is very much a male now producing fry of his own and he is the dominate male. At first he was pestered as much as the other females by the males. I don't know if this fish changed its sex or was just a late developer because I know swordtails can develope at different rates and times.

Last edited by tessa38uk at 12-May-2005 03:35

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I just had a swordtail change sex on me. It was DEFINATELY a female for about a year until recently after the male jumped out of the tank and died. She was the lone sword in the tank for about 3 months then, she developed a gonopodium and started growing a sword point on her tail. I have heard though that when they change sex like that they are sterile.

Dear FishyCharacter
I would introduce 2-3 females to the tank to find out if "he" is sterile...!!!
I think that the males are BORN males but they reach maturity at different stages. It also depends on the hierarchy. The Alpha male seems to "supress" the expression of sexuality of the others which they take the chance once the Alpha male is gone...

well...im still observing my female platy....when i bought her abt a month or so...her anal fin is well defined...lately...somehow..its fusing and almost resembling a gonopodium...only time will tell if she or he or whatever be what it will be (did i make myself clear...hahahaha!!!)

The reason I asked thsi question was prompted by a TFH back number article that I scanned and mailed to Clownygirl. In this article, it said that something interesting happened with male Swordtails. The first male to mature would become visibly and manifestly male (tail extension, gonopodium) and suppress the manifestation of full male characteristics in the others for a while. But, the first matured male would stop growing. Then, when the next in line had grown bigger, it would mature, develop male characteristics and take over as the alpha male. Then this one would cease growing, and the next in line would mature once it had grown bigger. Eventually, the social hierarchy would be reversed: the male at the bottom of the pile initially would mature latest, and be the largest once it did mature.

Only Clownygirl has a male Swordtail that is pretty small (which leads me to think that it matured early), and it is in an aquarium with two fairly large females. I'm thinking that its reluctance to mate may be due to the size disparity between it and the females. I did think originally, when pondering upon her lack of breeding woes, that the two big females many have been suppressed males, but thus far, they haven't (at least this is what I've extrapolated from Clownygirl's query) shown signs of becoming male. If the two females are actually suppressed males, this may have a bearing on Clownygirl not being able to breed with them. I also pondered the possibility of sex change being a factor in Swordtails, and wondered if this was having a bearing on Clownygirl's Swordtails. However, if the two big females are genuinely female, as opposed to being males that never matured, the fact that they are a large size would surely lead one to begin maturing, unless there is an age limit on this taking place of course.


Panda Catfish fan and keeper/breeder since Christmas 2002

my feeder guppies have pulled a sex change, when i kept them a few years ago. I seperated all the females and males- 2 of the females became males- gonopodiums, and became more colorful also.

All my platy fry were female, and now after about 3 months, they are all male!

The real question as to what sex said fish is, is this; "has that fish had fry and then turned male?" if so then I think you could say it was a sex change, otherwise I'd say it was just a very slow developing male...just as in humans, fish develop at their own rates for whatever reason...

So until they have fry they can still be considered male, after fry they are definately female, just my thoughts though, heidi

"I've got a great ambition to die of exhaustion rather than boredom." Thomas Carlyle

older swordtail females who have dropped fry have been known to change sex and grow swords. Not slow developing at all; just correcting imbalance.

Empty chairs at empty tables, the room silent, forlorn.

update on my last response....its confirmed....my female platy is now a male....his gonopodium acts as it!!! now...instead of having 2m/2f platies in my tank...there are 3m/1f....and my micky mouse platy who was very aloft most of the time became the alpha male now and guarding the single female like a hawk.