Swordtail sex change

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bobbi619

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Jan 17, 2003
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Hey all, I've heard of them changing sexes and now its happened to me. I had a male & female swordtail then added another female thinking he needed more action. The 2 females are now growing swords and have turned on the poor boy.
I heard this is a hormone thing, is it? What should I be adding to water of food to fix this problem?? Can they be changed back to girls??:confused:
 
I think the recent evidence indicates that sex changing in swords is the result of age, and is not reversible. I wouldn't risk adding anything that advertised to cause sex changes...If such a product exists, it's either bogus, or contains hormones you probably don't want lying around.

So, options are: you got old female fish who were past their reproductive prime, and have changed, or, more likeey, you purchased male fish that were too young to display their sexual dimorphism, and grew swords as they matured--perfectly normal. I'd try to get some fish that were closer to adult size to begin with.
 
Look for the gonopodium (sp?) anyway, it's the small fin-like structure centered on the bottom of the body near the anal vent. This will be a more reliable visible structure than the sword.

I'm with OG on the idea that they were probably just immature males.
 
I'm under the impression that this is not actually a sex change, but rather a late development of the male. I've seen the same phenonenon in guppies, resulting in a huge male fish!

What is needed is for someone to document a 'female' who is definitely a female - i.e. has had fry turn into a functional male. To the best of my knowledge, this has not happened.
 
And I can't recall where I read this--one of the trade magazines, I know, but it stated that elderly female swords would take on male morphic traits and behaviors, though there was no mention of the fish having successfully reproduced prior to conversion nor of a successful fertilization following the physical change. The larger size compared to a 'normal' male was noted.

Sigh--scientific documentation of such things is difficult. Try getting a grant for it sometime. :)
 
I think Orion Girl's on target as usual. I recently learned that sex isn't fixed in the chromosomes, as it is for birds and mammals, but it's plastic to start with and can remain quite flexible.

Look at those marine fishes with wacky sex lives, Amphiprion Clownfishes that develop from male to female if the dominant female is removed... And some wrasses maybe?
 
Quite a few wrasses, with a few cases of fish where there normal reproductive cycle is to be female for the first year, then change to a male for the remainder of their life. Active, happy reproducers that play both sides, at different times.
 
I was under the impression that it had to do with hormones in the water. I've bred swordtails before and have never gotten a male to develop. I've kept the babies for nearly a year before trading them in. In addition, I think that if sex change had to do with age, you would see more of these "giant" males out there. I know my female f-2's (?) are always larger than the ones that you normally see in the LFS, and if any of these were to change into males, these too would also be larger than the males seen in the LFS.
 
From my researches....

Sex is chromosomally determined in some fish, swordtails included. But not others - such as the wrasses.

However, there certainly is something odd with swordtails. This link http://www.alumni.caltech.edu/~copeland/work/fish.html briefly mentions it - and why you might get all males from a particular pairing, but doesn't explain how you'd get all females.

IIRC from another source (not online, and I can't find it), the YY males develop earlier than the XY males. As the XYs look female until they develop, and whilst their YY brothers have already changed, this gives rise to the story that swordtails change sex.

I'm sure this is all going to change the next time someone studies it.

[addendum - just found another page that states that swordtail sex determination is polygenetic - lots of genes contribute to whether a fish is male or female.... :rolleyes: ]
 
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I don't know if this adds anything to the discussion, but we had a solitary male "redwag" sword at my lfs in a 40 gal for about a year w/no other livebearers. I think the tank actually was housing a few large silver dollars or something, but after a year it lost the gonopodium and "sword" on the tail. I was always under the impression that these guys changed sex to accodomate for poor male/female ratios. Of course I never did any further looking into the topic.

I can't vouche for any reproductive accounts either way w/that particular fish.
 
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