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Author Topic: Swordtail sex change  (Read 13299 times)
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« on: June 09, 2010, 07:12:14 PM »

A commonly repeated misconception that is seen in many places on the internet and even here in the species profile is that a swordtail can change sex. It is simply not true. A swordtail has its sex determined genetically in much the same way as we mammals do. It also has an X and Y chromosome setup just like us. A female can, with advanced age, show signs that make it appear to be a male because it has lost its hormone balance as it ages. The same happens to a lot of human females who will grow a bit of a mustache when they are getting on in age and their hormone balance is no longer as good as it was when they were 20.
Another very common situation that we see is what are sneaker males. These guys are trying to hide their gender to avoid the very real danger that some dominant males can pose. I have seen wild type males in my own tanks take over 18 months to allow their gender to be displayed. I had 6 of what looked like juvenile females in my tank and when one showed signs of being a male at about a year old I thought maybe I would start to see some breeding activity. There were not only no fry in the tank, but the late developing male did not seem interested in the other fish. As time went by I grew to understand why he was not interested. One by one until an age I would estimate as almost 2 years old, each of the remaining males in the tank let his gender be known. I never had a female anywhere in the tank, hence the lack of breeding interest.
A male swordtail that develops late is often a very large fish who is a definite looker. They are very solid and tough looking compared to their rather wimpy looking early developing fellow males. The early males never do achieve the grand proportions of a late developing male.
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« Reply #1 on: June 09, 2010, 11:55:46 PM »

We do not spread that misconception here. Smiley

I have witnessed male swordtails hide the fact that they are male by not growing a sword until they are older. It's a simple way to protect themself.

A dominant males sword will also have a small growth spurt if you dare to add another male to its tank.

     "Give others freedom to be themselves. Appreciate the differences between their ways and yours."
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« Reply #2 on: June 11, 2010, 04:27:20 PM »

  On this particular concept, I have an open mind.
  Our knowledge and understanding of Nature is constantly expanding and changing.  If you tried to tell naturalist 100 years ago that there is a species of fish composed entirely of females or that a there is another species that can store viable sperm for many months he would scoff at you since he KNEW that these ideas were both impossible.
  This particular idea has been around for a long time and it is such that it would be difficult to absolutely prove one way or the other.  But most of the evidence for or against it is anecdotal and therefore cannot be accepted as proof.
  Sterba's Freshwater Fishes Of The World (1973) was for years considered one of the best sources of knowledge about fish and it contains the following passages.  (I don't contend that this is proof of the concept, but it does show that there is some support for it among authoritative figures)

* Page 556.txt (0.7 KB - downloaded 379 times.)

* Swords.jpg (64.67 KB, 640x417 - viewed 1345 times.)
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