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Can guppies change their sex?

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I've read both YES and NO all over the internet while trying to look for a credible answer. Alas...I am still not sure whether they do. It was my impression that this was a myth due to the females being able to hold sperm for so long thus confusing pet owners into thinking she must have been impregnated by another female tank mate.

However, the closest credible reference was this: http://www.fish.wa.gov.au/docs/pub/IMPF ... 6.php?0506

...which says that they can!

I still don't believe it...

Anyone got proof? hehe

I've even tried to search peer reviewed journals but nada!

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I've just found this statement...but I can't find the article through the uni library (they are probably not subscribed to the journal anyways):

WINGE (1923, 1927) has shown in the West Indian guppy, Lebistes, that the X and Y occasionally cross over. In 1930 he stated that the genotypic chromosomal constitution of XX for femaleness in this fish may be overruled by other sex-determining factors so that the XX complex may occasionally produce a male. These XX males when mated to normal XX females produce, as might be expected, IOO percent daughters.

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lol i figured it out

i was reading to many threads at once :oops:

what i meant to say here was..

Yes guppies can change sex, several people here have first hand experience of it. Closest i've seen was an almost adult male with a gonopodium change to female shape, lose colour and his gonopodium changed to female shape, didn't get to see if s/he could have babies though.

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Yep, definitely.

Most occurences are females changing to males, these are called XX males and is a tool used by Asian breeders to produce all female guppy offspring. This phenomenon, as Simian has pointed out, occurs in female only groups.

Males changing to females are usually sterile and also a technique used by Asian breeders so that you cannot have any offspring from the good stock that you just bought so eliminates competition.

Another technique they use to change guppy sex is subjecting them to hormones of the opposite sex, male introduced to female hormones and females introduced to male hormones.

Our aquarium fish population for trade is not big enough for this kinds of tricks and hopefully it will never come to this.

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if you search a few pages through the livebearer threads you should be able to find the ones where this has been discussed before :)

Yeah, I have googled it, but there weren't too many credible accounts out there. Just a lot of people arguing back and for that they read this or that, or they have guppies that looked like females but then turned out to be males...fairly unconvincing stuff.

Yep, definitely.

Most occurences are females changing to males, these are called XX males and is a tool used by Asian breeders to produce all female guppy offspring. This phenomenon, as Simian has pointed out, occurs in female only groups.

Males changing to females are usually sterile and also a technique used by Asian breeders so that you cannot have any offspring from the good stock that you just bought so eliminates competition.

Another technique they use to change guppy sex is subjecting them to hormones of the opposite sex, male introduced to female hormones and females introduced to male hormones.

Our aquarium fish population for trade is not big enough for this kinds of tricks and hopefully it will never come to this.

That is very interesting. I did come across that with people in Japan breeding these xx males or even super males (YY) in order to manipulate the sex ratio or sterility. But in the normal population this 'strain' doesn't necessary happen very often right? I mean, only rarely will a female turn into a male in people's personal aquariums. It is my understanding is that the chromosomes controlling sex are usually a different size in most animals, but in some including guppies they are similar in size and therefore prone to mix up and cause phenotypic sex versus genetic sex to be different. For the most part I think that many people get confused by the fact that they buy several females one of which was already loaded or had stored sperm and then assume that the females must have mated together.

Anyways, thanks for your replies. I wanted to clear it up for myself once and for all and I was tired of reading all the lame responses on 'yahoo answers' by people that didn't know what they were talking about! Probably didn't even realize that humans can have XXY or YY as well nor how hormones actually work to bring on secondary sexual characteristics and kept arguing that it was not possible at all because fish cannot change their reproductive organs. Ugh.

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something I have read about mollies which may apply to other livebearers is that an apparently female young fish is actually male and becomes male in appearance later ie on maturity. They supposedly mature late but into great looking fish. I have had a fish do this but s/he died before I could establish if s/he was fertile as a male. It was purty though

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Try this book Sex, color, and mate choice in guppies

By Anne E. Houde. It's on Google Books - this link should take you straight to the page about xx chromosomes, but I'm not sure if it's exactly the right one for this question (I got tired of waiting for it to lod up on my dial up connection).

http://books.google.co.nz/books?id=ZOlB ... q=&f=false

I read a hard copy of the book (had to interloan it through my library) and I'm sure it talked about the fact that females do become hormonally male and can inseminate a female and produce babies, but because the 'male' still has XX chromosomes, the babies are all female. (But can still 'become' male the same as their father did.). In practice I had always thought that keeping a tank of just females would make some change to male.

For those of you searching Google and being frustrated by the bumf, try Google Books ( as above) or Google Scholar scholar.google.com. Then you'll get scientific material. Often the abstracts are enough, but if you really want the article, you can interloan it through your library. There will be charges for that, but it's up to you whether the cost is worth the gain.

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Yep, definitely.

Most occurences are females changing to males, these are called XX males and is a tool used by Asian breeders to produce all female guppy offspring. This phenomenon, as Simian has pointed out, occurs in female only groups.

I just had a female change to male not long ago, there were only 3 young females in the tank and suddenly there was 2 female and 1 male. 1 f is now looking fat and full of fry so looks likely they will be all female going by the post above.

I have also seen a balloon molly change sex, also from female to male, I found it strange as there was already a large male in the tank, unfortunately they all died so I have no idea what would have happened when they bred

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Oh No! We have separated our males and females as we were getting overrun by guppies. No one warned us when we got the first two.

Now you tell me that won't work either!! They are unstoppable super breeders!! :o

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Oh No! We have separated our males and females as we were getting overrun by guppies. No one warned us when we got the first two.

Now you tell me that won't work either!! They are unstoppable super breeders!! :o

Which pet shop do you go to? If you talk to Tracey and Richard they may buy some of you guppies from you lol

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Hi, Yes we gave them some from the 2nd lot of fry. We are waiting till the others are big enough not to get sucked into their filter .

we love that shop - in there every time we go to town.

DD (8) got some ideas that perhaps she could make her fortune from selling guppies! LOL :D

Meanwhile DD (7) has decided she would like a fishtank too and is naming all the guppies she wants to keep! Sigh :roll:

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Oh No! We have separated our males and females as we were getting overrun by guppies. No one warned us when we got the first two.

Now you tell me that won't work either!! They are unstoppable super breeders!! :o

hate to say it but i found something that stops the over run of fry.... bolivian rams!!! i added some to our tank and havent had babies since.... now i want fry!.... dam rams, just as well theyre pretty

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Hi, Yes we gave them some from the 2nd lot of fry. We are waiting till the others are big enough not to get sucked into their filter .

we love that shop - in there every time we go to town.

DD (8) got some ideas that perhaps she could make her fortune from selling guppies! LOL :D

Meanwhile DD (7) has decided she would like a fishtank too and is naming all the guppies she wants to keep! Sigh :roll:

LOL, very funny!!! I used to do those tricks on my father when i was a child....

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I am on this thread because I had four male guppies. I use the words had... because one is now looking very fat and the other three keep trying to mate with it. I got four males as I was already over run by molly babies (from a different tank...) please tell me the males cant change and get pregnant? 

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On 9/20/2020 at 2:57 AM, Zennifa said:

I am on this thread because I had four male guppies. I use the words had... because one is now looking very fat and the other three keep trying to mate with it. I got four males as I was already over run by molly babies (from a different tank...) please tell me the males cant change and get pregnant? 

I'm looking for the same question as my daughter has 8 males and a few are looking very fat but from what I've read males can change to female but they can't have babies as someone said above i would like to know if its true to 

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Guppies can change sex but also note male guppies will attempt to mate with anything that moves, from what I have observed, regardless of what sex it is.

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