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livebearer producing the most fry


The Doctor
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Just be advised that with swordtails, some of the presumed female swordtails can turn into a male. I have a large breeding colony of neon swords and have smaller colonies of selected swordtails in other tanks in case my big colony collapses. In one of those tanks I had a lone male, so I selected a large female from the big colony for him. He did the spawning routine with her, and I was waiting for fry. I'll be waiting a long, long time as "she's" now developed a gonopodium and is starting to develop a swordtail. "She" was about twice the size of the male and slightly older than him, but either changed sex or was a very slow developing male.

I had the misfortune to spend fifteen days in the hospital a few years ago and a tank with eleven swordtails had no food and their light was on 24/7 for those fifteen days. When I went into the hospital I had three males. When I came out there were nine males. It appears that when stressed female swordtails decide to become male swordtails. Male swordtails sell better than females, so there's probably a way to stress them enough to get more males, but I've never heard of anyone doing it commercially.

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Reportedly, all young swordtails have both sexual organs/gonads and then absorb one or the other becoming either male or female. Some late blooming males have reportedly had one or more spawns delivering fry before absorbing the female gonads and becoming male. Males can't become female once they've made the switch, but a supposed female, even one that's given birth, can become male. It's an interesting phenomena. Based on my very limited experience (I don't generally try to stress my fish) I suspect stress (24 hour a day lighting and no food for two weeks) can provoke the change. With fully developed male swordtails having more market value, it could be an interesting experiment for a fish farm or research facility to conduct to see if they could stress supposed female swordtails into becoming male or prompt late developing males into developing sooner.

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12 hours ago, The Doctor said:

I have done research on this , it is not that the females become males, but some males develop later in life to avoid being dominated by another dominant male... but a great reminder, to watch what are you buying 🙂

Swordtail guru Ted Coletti had a very interesting interview with @Randy that included this very issue on a recent Aquarist Podcast.

 

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3 hours ago, Ken Burke said:

So, three combinations are female, two are male!  How cool is that

That blew my mind when I first learned that about platys. You could potentially get a pair (xx and yy) that only produce male babies. How weird is that?? I hear that the ww females don’t exist in nature though, so unfortunately no only-female-producing pairs. 

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