# molly changing gender



## zoea (May 6, 2011)

I'm gonna start by saying I've been breeding mollies for years, I have over 150 and in my tank i will be discussing, I have about 12 females and 4 males. I bought a beautiful female sunset sailing Molly from a local petstore. I had also previously bought a 2.5 inch male sailfin Molly who until I got the sunset Molly, was sexually passive, never mated with any of my females. When I introduced the female sunset molly, he couldn't get enough of her. Constantly chasing and poking with its g fin. A few months after having the sunset molly, its rear fin began to change from fanned out to long and thin. Before I knew it the Molly was a boy! I looked it up and though its rare people have reported this. Because its rare most pass it as human error and that they're just wrong. But out of the research ive done, I think it may be possible that its a genetic abnormality. Please speak up if this has happened to you or someone you know so I can continue my research


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## msawdey (Apr 6, 2009)

I have heard of this happening before in certain species. With mollys and platys, with as much as they reproduce and have a tendency to interbred, i wouldn't put it past them. You breed enough times, your bound to get mutations and i wouldnt doubt that something like this could happen in a blue moon..


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## zoea (May 6, 2011)

I've read its documented a lot with swordtails and sometimes guppies i figure nothing impossible. Some say it can happen when they are removed from a group and put on a new one they will establish themselves as dominant to be cheif and in turn hormones go way up and they change into a male. I read that somewhere so sorry if i didn't give proper due credit.


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## msawdey (Apr 6, 2009)

that actually makes complete sense. I know certain species of birds can do it and like you have read that fish can also. Especially african cichlids


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## BBradbury (Nov 8, 2010)

*Gender Change*

Good morning zoea...

Had a similar experience with one of my Fancy Guppies. This fish had the characteristics of both sexes. Had the larger and plumper female body, but the finage of the male.

There was no color in the body, similar to a feeder type Guppy. This fish grew quite large even for a female and lived almost two years, which is quite long for a Fancy Guppy.

The occurance is called "Sex Reversal". This happens relatively often with "Livebearers". The research I've done gives the reason as fry have the potential to be either sex. It just depends on conditions as to which organs grow quicker. It essentially has to do with hormones and the environment.

Apparently, in the wild, this type of thing happens due to pollution.

Peter Scott wrote briefly about this in a book called " A Fishkeepers Guide to Livebearing Fishes". I have an old copy dated 1987. Interesting reading and good information, I use it often.

B


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## zoea (May 6, 2011)

Thanks so much for your input!


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## FishFarmer (Feb 8, 2007)

I know for a fact that swordtails can change sex. I had one change from female to male--I though I was going crazy and seeing things!


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## zoea (May 6, 2011)

I think it can only happen if the female hasn't been pregnant yet


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## Hannothan (Dec 26, 2010)

No, it can happen after a female fish has been, or is pregnant. I had a female molly change genders, and with a gonopodium, spit out some fry.

It's not every day you see a "male" fish give birth. It was crazy.


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## Lil' Swimz$ (Jul 24, 2010)

I swear I've had a hermaphrodite cherry shrimp before. Color and size of a female, tail of a male, and no saddle.


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## Ichthyologuest (May 5, 2011)

Fish changing gender is actually much more common that you would think. There are a couple reasons for fish doing this, and different species change for different reasons. The easiest way to rationalize why fish do this is to understand that every fish wants to spread their genes to as many offspring as possible. Some fish are capable of changing if they spend prolonged activity in a population that is predominantly one sex. For example, a male fish in a predominantly male group has little chance of competing with the other males and successfully producing offspring. It is most advantageous for this fish to make the effort to change sexes, which will allow it a much greater chance of successful reproduction. Competition also forces sex changes. In the case of the black sea bass, almost all fish are born female. As the fish grows larger, it turns male. This means that almost all large sea bass are male. Juveniles start as females because it would be impossible for them to successfully compete with these enormous older males. The females then change once they become large enough to compete, since being a female is no longer advantageous (the cost of producing eggs is much greater than the cost of producing sperm). 

To cut my long story short, what you experienced is definitely not a mutation, just an occurrence that while uncommon in the hobby, or in that particular species, occurs more often than you would expect in unbalanced wild populations of many species. It is possible the change started occurring weeks before you purchased the fish, when it was contained in a stressful or predominantly female environment. The more you know!

Sources: Marine Biology bachelors degree.

Also lil' swimz is right, this is even more common in shrimp and other invertebrates than in fish.


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## chicken (Aug 22, 2007)

I've read that one explanation for this phenomenon is that the "female" is actually a very late maturing male.


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## d3snoopy (Apr 1, 2011)

I have a sword tail do that. Bought a male and 2 females from the LFS... about a month later I had two males and one female. I still have the one that changed...


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## zoea (May 6, 2011)

Thanks for all the info! I read a thread there a girl asked if it was possible and said how she had been breeding for years and wondered if this occured with avyone and they jumped on her like hyena about how she didnt know anything and they kept referring her to pages on how to breed fish correctly. I hope she reads this and sees that she was right regardless of what those others said


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## sewingalot (Oct 12, 2008)

I've seen it once with a guppy fish. I thought it was a late bloomer, but it looked just like a female and one day turned into a male. This was a younger fish, but when I researched it, I did read several places claiming it is possible. I think it is entirely a survival technique.


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## zoea (May 6, 2011)

Yeah I totally agree


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## Guest (Nov 4, 2013)

*Molly Sex Changing?*

well i thought i was crazy but i have 2 30 gal tanks one for males and one for females after about 3 months i had 4 males in the female tank and a whole lot of baby's so i removed the males thinking i had just missed them 2 to 3 months later theirs 2 more males i have had molly's for years and it seems that my orange sword tails are changing sex each time i also removed every thing from the tank including marbles and made sure to extract every baby
as of today i have done it again leaving only 10 females but my guess from what i have seen there will be males eventually and less females what i find strange is that the males are not changing to females any way at least i know im not the only crazy person lol


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## Guest (Mar 8, 2014)

*freaky*

Ok... im glad I found this. My "female" Balloon mollie that give birth 2 months ago to 23 fry on a breeding tank where "she" was alone to give birth, changed to male!!! I though I was going crazy! Now it Is chasing around the females and has grown male genitals!!! "She" is massive and looks pregnant! But its a male now! I Guess that gender change on mollis is possible.


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## Guest (Mar 12, 2014)

*My mollies just did !*



zoea said:


> I'm gonna start by saying I've been breeding mollies for years, I have over 150 and in my tank i will be discussing, I have about 12 females and 4 males. I bought a beautiful female sunset sailing Molly from a local petstore. I had also previously bought a 2.5 inch male sailfin Molly who until I got the sunset Molly, was sexually passive, never mated with any of my females. When I introduced the female sunset molly, he couldn't get enough of her. Constantly chasing and poking with its g fin. A few months after having the sunset molly, its rear fin began to change from fanned out to long and thin. Before I knew it the Molly was a boy! I looked it up and though its rare people have reported this. Because its rare most pass it as human error and that they're just wrong. But out of the research ive done, I think it may be possible that its a genetic abnormality. Please speak up if this has happened to you or someone you know so I can continue my research


I bouth some mollies and made sure I had 4 females 2 males and now I got four males and 2 pregnants females.. I'm not sure but it started to happen after the 2 females got pregnants and I phoned the local petshop and they told me it cant happen just like that.

well it did...


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## R_Vandermeer (Sep 8, 2014)

I had what I thought were 3 female Gold-dust Mollies, 2 of which were heavily pregnant. I was hoping to see my larger female drop her fry, but a few days later I had seen no fry and she had slimmed down considerably. A few days after that I was shocked to find that her fin had changed and now SHE was a HE! I am amazed


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## Bananableps (Nov 6, 2013)

At the end of the day, does it really matter what gender your molly is? All your molly needs is to know that you love and support it, no matter what he or she decides to do in life.


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## sewoeno (Apr 12, 2014)

i had a molly do this! in the end i was sick of live bearers and gave it back to the pet store.


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## wendyjo (Feb 20, 2009)

TyrannosaurusSex said:


> At the end of the day, does it really matter what gender your molly is? All your molly needs is to know that you love and support it, no matter what he or she decides to do in life.


roud:


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## PortalMasteryRy (Oct 16, 2012)

TyrannosaurusSex said:


> At the end of the day, does it really matter what gender your molly is? All your molly needs is to know that you love and support it, no matter what he or she decides to do in life.


Sounds like a speech for another species. LOL.


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## xmpjx (May 31, 2015)

Read this the other day thinking how rarely this must happen. 

I just noticed today one of my mollies changed gender... Haha!


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## NotCousteau (Sep 25, 2014)

I had a female swordtail that turned male. It was fascinating to watch the change. Post photos!


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## amcoffeegirl (May 26, 2009)

Can it only be a female to male change? Is it possible that all fish start out as female? 
Are these late bloomers?
It is hard to believe that one could give birth and then change.


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## dpod (Sep 16, 2014)

I know there are a lot of fish that can switch genders, but it's usually unidirectional. I've had Swordtails switch from female-->male, but never the other way around. Some marine fish like wrasse and clownfish switch genders as they mature, depending on what's going on in their little colony. IIRC, clowns start out male; at the bottom of the pecking order. When the female who's the boss of that particular coral head dies, the males all shift up in rank and the top male becomes the new female.

Fishes are weird, yo


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## familyforever (Jan 2, 2019)

yes i think that our black male molly has changed into a female cause it looks like it is preganet. so i guess it is possible that them change gender. and thanks for your help..


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## bobby123 (May 17, 2019)

Yes! this happened to me. I bought two Golden Doubloon Mollies, they looked fully grown. I picked out two females because I only had a male and female at home. The one male sadly died of fin rot leaving me with three lonely females. Today I looked in and noticed one did not have the normal round belly like they have had since I bought them many months ago. She was now slim like my other male was and her anal fin had switched from a fan to a point.


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## Bio Ed Doc (Mar 5, 2021)

Ichthyologuest said:


> Fish changing gender is actually much more common that you would think. There are a couple reasons for fish doing this, and different species change for different reasons. The easiest way to rationalize why fish do this is to understand that every fish wants to spread their genes to as many offspring as possible. Some fish are capable of changing if they spend prolonged activity in a population that is predominantly one sex. For example, a male fish in a predominantly male group has little chance of competing with the other males and successfully producing offspring. It is most advantageous for this fish to make the effort to change sexes, which will allow it a much greater chance of successful reproduction. Competition also forces sex changes. In the case of the black sea bass, almost all fish are born female. As the fish grows larger, it turns male. This means that almost all large sea bass are male. Juveniles start as females because it would be impossible for them to successfully compete with these enormous older males. The females then change once they become large enough to compete, since being a female is no longer advantageous (the cost of producing eggs is much greater than the cost of producing sperm).
> 
> To cut my long story short, what you experienced is definitely not a mutation, just an occurrence that while uncommon in the hobby, or in that particular species, occurs more often than you would expect in unbalanced wild populations of many species. It is possible the change started occurring weeks before you purchased the fish, when it was contained in a stressful or predominantly female environment. The more you know!
> 
> ...


Thank you for speaking out with scientific knowledge.. Here is an interesting link that discusses the subject. Fish are the sex-switching masters of the animal kingdom


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## JJ0000fishCurious (Sep 16, 2021)

Here’s my story,
I’m kinda new to the whole molly breeding thing and I’ve been trying to figure out what happened to my fish. So I had 3 mollies one Dalmatian male one Dalmatian lyretail female and a golden panda lyretail female in the same tank but then I realized my golden panda molly was already pregnant when we got her so she started Getting picked on and I transferred her to a maternity tank the two others were doing fine the female was more aggressive than the male but was better after the second female left. I went on vacation and when I got back I realized that my Dalmatian female had gotten larger, darker. Now today I realized that her anal fin is not what it used to be she now has a g fin!? So I’ve been trying to figure out what the heck happened and that’s how I got here. She changed into a male but I don’t know why because she’s in a tank with only a male molly and a male pleco. If anyone knows why she is now a he please let me know


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