Swordtail Sex Change: Myth or Reality?

[tr...@io.com]

I recently separated out the female live bearers who we want to spawn
the next generation. One of them was a "female" pineapple sword
about 2" long with a nice triangular anal fin. Now, about two weeks
after moving her to an all female tank that fin is looking awfully
thick along the edge.

Do swordtails change sex?

I was reading archives over on some site (forgot the name) a few weeks
ago where they have (or had) folks to answer email questions. One of
the responders insisted in multiple postings that swordtail sex change
had been shown to be a myth in research. Apparently there is a
distinct chromosomal difference between male and female swordtails.
Fish which are known sex changers do not have sexually dimorphic
chromosomes. And they did some study where they observed a bunch of
swordtails or something.

On the other hand, I have read numerous anecdotal reports of female
swordtails appearing to become male in the absence of any other male
and that appears to be what's happening here. Then again, the
plural of anecdote is not data. :-)

On the gripping hand, it is possible that this lad (gal?) just hadn't
matured yet. We raised her in our tanks and she's not all that old.
But I figured at 2" long she would be showing a gonopodium if she was
a he. Also she has the thicker body (ventral to dorsal)
characteristic of females. Male swordtails are usually shorter in the
ventral-dorsal dimension.

Jeff Walther

[Melissa phillips]

Swordtails do not change gender.  However, half the males show up as males when young.  These guys usually stay small.  The other half show as male once they are older, and get big.  In a study on mate preference with swordtails about half the females liked small males over large males, the other half preferred big ones over little ones, hence the continued presence of both.  The bigger males often take on the body type of a female and will not show their specialized anal fin until they get to a certain size/age.  Sort of a delayed puberty I guess!



--
Melissa:)

[tr...@io.com]

Thank you, Melissa! That exactly answers my question and is a
conclusion completely consistent with my observations. I don't why,
but the business was causing me disproportionate anxiety--perhaps
because it was messing with my careful breeding plans. I really
wanted that Pineapple to be female, or failing that, to clearly be
some sex so I would know how to proceed.

So now I know, off he goes, back to the mixed swordtail tank, unless I
want all my female swordtail breeding stock impregnated by him...
which is not a farfetched choice. Because the pineapples are no
longer available locally, one of my goals is to establish reliable
breeding stock of that variety in my tanks.

So this pineapple swordtail must be one of the late maturing large
bodied males. Hmmm. I started with slim bodied males (1 green, 2
pineapple). But most of my males now are of the thick bodied
variety.

Do you know if the male body type is genetic or do environmental
factors play a part? A couple of my green swords matured as the slim
body type, but in the ones which appear to be green/pineapple crosses,
most (all?) of the males are large bodied.

Thank you again. It's nice to get a clear non-ambiguous answer. So
often, there are so many variables involved in this hobby that the
answers are much less clear cut.

Jeff Walther

[Melissa phillips]

I believe whether they mature earlier or later is more genetic, but environment does play a role to an extent (as it does with almost anything).  The presence of more late bloomer big bodied males or more skinnier males has to do with selection on the females part.  For example if all your females prefer bigger bodied males . . . you will eventually end up with all big bodied males.  The females preference is, I believe, genetic, so if mommy liked big guys, daughter likes big guys.  If I come across the studies anywhere online I will post the link, but the first time I read it was in the college library while I was skipping zoology and educating myself:)  I used to skip classes a lot as I read the text books the first week, then I would go and read books that had to do with the subject I was skipping . . . . worked great to expand my knowledge, but not so much help in expanding my grades:)

--
Melissa:)

[NetMax]

On Jan 21, 6:00 pm, "t...@io.com" <t...@io.com> wrote:
> I recently separated out the female live bearers who we want to spawn
> the next generation.   One of them was a "female" pineapple sword
> about 2" long with a nice triangular anal fin.   Now, about two weeks
> after moving her to an all female tank that fin is looking awfully
> thick along the edge.
>
> Do swordtails change sex?

Some people think so, but I had to dig pretty deep
abstract:
http://tinyurl.com/36ncof

pdf:
http://www.biolbull.org/cgi/reprint/51/2/98.pdf

NetMax

[Frank Bayne]

 "Melissa phillips" wrote:
> Swordtails do not change gender. However, half the males show up as males
> when young. These guys usually stay small. The other half show as male
> once they are older, and get big.

 

       Hi Melissa,

       I bred and raised swordtail (hi-breds) for quite a few years. As soon as I could sex them, males went in one tank and females in another untill they were eather sold or picked as breeders. I never had any change gender, and would have to see it to beleave it. With swordtails, their color gene has somewhat to do with when they can be sexed, some while they young (3 mos.) while others when they are much older (1 year). I mainly bred black hi-fin lyretails and unlike most other varietys, they take almost a year before you see male characteristics (about 2.5" to 3" long, and up to 1.5 years for a fully grown sword.

 

>In a study on mate preference with
> swordtails about half the females liked small males over large males, the
> other half preferred big ones over little ones, hence the continued presence
> of both. The bigger males often take on the body type of a female and will
> not show their specialized anal fin until they get to a certain size/age.
> Sort of a delayed puberty I guess!

        Hmmm - I don't remember any of my female breeders ever having the chance to have a "preference" - they always seemed to try to get away from the male, no matter what size he was!  I found that body size could be an enviromental thing - lots of food and a deep tank seemed to make larger fish, both male and female. But by selective breeding, one could get giants. My breeder Hi-fin Lyre-tail Berlin (black body red fins and tail) Swords were giants - females were 6" to 7",  2" around and would drop 200+ fry per batch - the males however were a little over half that size. That is done by genetic line breeding............. Frank

 

[tr...@io.com]

Thank you, Netmax. An interesting article. I may try to find the
archive I was looking at with the fellow who was so convinced that
they don't. He may have referenced a research article with the
opposite conclusion. I'd like to read both and compare.

The fact that the specimens in the above article gave birth before
changing form, pretty well establishes that swordtails can change
their appearance. I would still be hesitant to accept the conclusion
that the transformed males were fertile. The author says they
impregnated virgin females, but he didn't give any details about how
they obtained those virgins. If swords are raised with their
siblings, it can be awfully hard to get all the new males out before
they have a chance to impregnate anyone. So the only way to be
certain you have virgin female swords is to raise them separated from
their siblings, one to a container, which they may have done. On the
other hand, they did say that all the proper bits were in place when
the examined the poor things internally. Hmmmm.....

Jeff Walther

[Melissa phillips]

I wonder if it has to due with species of swordtail, maybe some can and some can't?  The article I read in college was very much saying that whatever species of swordtail they experimented with that they did not change gender.  Hmm. . . Wish I could find it.  I know that the males that turned later showed a gravid spot while they were camo'd as female.  The ones that transformed from female to male, where they genetically female?  Did they possess extra chromosomes? 

On Jan 23, 2008 10:59 AM, tr...@io.com <tr...@io.com> wrote:

On Jan 22, 3:57 pm, NetMax <computeral...@hotmail.com> wrote:
> On Jan 21, 6:00 pm, "t...@io.com " <t...@io.com> wrote:

> > Do swordtails change sex?
>
> Some people think so, but I had to dig pretty deep
> abstract: http://tinyurl.com/36ncof
>
> pdf:http://www.biolbull.org/cgi/reprint/51/2/98.pdf

--
Melissa:)

[Tynk]

I remember back when I was in Junior High (middle school to some), I
had a 10g with some nice swords.
I had a "female" go male. I have no idea if this "female" ever had any
fry, as I had a few females and wasn't really keeping track.
I watched this fish develope, just like a juvie live bearer, only it
was good sized "female looking" fish.
Just like a juvie male, the gonopodium changed gradually and a sword
developed.
I had always assumed they changed genders and back then people did
know about this happening so it really wasn't any real big deal.
It was more like...."Hey, I got one of those that are changing too.
Neat."
Of course I have no idea if this was a fertile male.
He surely acted like a male though.
That was the only sword I had change. Although, I'm not really into
them and haven't had them too many times.

[Gill Passman]

Well I don't know about Swordtails but certainly there are fish that
change sex and from what I've read it is most often from female to
male - one exception being the Clownfish.

Clownfish start off as male. The dominant male becomes female and
picks a mate. If the female then dies the dominant male becomes the
female and picks the next male in the pecking order as its mate and so
on and so on. So a female clownfish can initially have fathered fry
before becoming a mother.

Raises all sorts of questions about the biological accuracy of Finding
Nemo - as Marlin would have become Marlina when Coral died and would
have sort of been Nemo's Mother as well as biological father. But I
guess that scenario would have just been too complicated for a kid's
movie - lol

Gill

[Melissa phillips]

And then nemo would have become his mom/dad's mate . . . .

I used to tell my customers that all the time after the "LOOK ITS NEMO!"  Weirded them out and they stopped calling all the freaken clownfish nemo.

Many gobies change gender as well.  If you want a group of gobies you need to buy them all at the same time and make sure they weren't separated, or the females will start turning into males.  Many wrasses do the same, if there aren't any males around the dominant female becomes a male.  Although, i don't think i've ever seen bird wrasses change, but I have seen many fairy wrasses change . . . came into the store as a female . . . didn't sell because they were a bit drab, turned into a male, we raised the price accordingly and they sold:)  The thing is with these fish, I do not think chromosomes is what determines male and female, like with swordtails.  Anyway, its all pretty interesting!

Raises all sorts of questions about the biological accuracy of Finding
Nemo - as Marlin would have become Marlina when Coral died and would
have sort of been Nemo's Mother as well as biological father. But I
guess that scenario would have just been too complicated for a kid's
movie - lol

Gill

--
Melissa:)

[tr...@io.com]

On Jan 23, 10:31 am, Gill Passman <g...@taylorpassman.co.uk> wrote:

> Raises all sorts of questions about the biological accuracy of Finding
> Nemo - as Marlin would have become Marlina when Coral died and would
> have sort of been Nemo's Mother as well as biological father. But I
> guess that scenario would have just been too complicated for a kid's
> movie - lol

<snicker> Hilarious. I never thought about applying clownfish sex
changes to Nemo. Hee, hee.

Jeff Walther