That is a really interesting read! Thank you so much for your very detailed reply ☺️If this specific specimen has got no gravid spot shown, then this specimen is a late male. If it does show a gravid spot, it's a female that changes into a male. Both ways, will show a more ferm build bodyshape than a normal developing male. And looking at the size of the sword of this swordtail, it shows that this sword has recently started to grow. Typical for a female transitioning into male and also typical for a late male.
Not all female swordtails can change into males. There is an autosomal locus with two alleles, A and a, which affects sex determination in XX fish. If the genotype is AA, the fish will be female and remains a female, and if aa, the XX individual will be male. Aa genotypes are predominantly female and can change into a fully functional male. Aa genotypes are born with both male and female gonads. So, if you want to use the word hermophrodite in swordtails, you're really talking about an Aa genotype female. Such specimens will become a 100% functional males.
Male swordtails can not change into a female. For the transition of the analfin into a gonopodium is irreversible.
Really old swordtail females that have stopped reproduction, will undergo a hormonal change. This hormonal change triggers an overactivity of the MSX genes. The MSX genes are responsible for the morphological change in finnage in swordtails. This results in an elongated analfin and elongated outer finrays (mostly the bottom finrays) of the caudal. In that way, it seems as if such an old female looks a bit like a male. But in fact, she's still a female and not changing into a functional male.
There are people who just don't believe that swordtail females can change into a male. For they only think that there are only XX female and XY males. And nothing in between. They call it an urban story. Even a lot of very experienced swordtail keepers that have kept and bred swordtails throughout many years, still think that it's not possible. And the funny thing is, that this phenomenon has already been researched and proven back in the 1980's. But not that many people know the existance of it.
Same thing with the platies. It's just that the sex change works a bit different than in swordtails. In platies there are 5 different sex genotypes instead of just 2. That's because of the W sex chromosome besides the X and Y. In fancy swordtails this sex chromosome "can" also be present as a result of the mix up of swordtails and platies to create more fancy strains. In such a case, a lot of those swordtail specimens are of the WZ or ZZ combination besides XX, XY and YY. ZZ is a structural female. WZ however can be specimens that have both male and female gonads that predominantly female but can change into male. I use the word "can" because not all females of that combination will turn into a male. In most cases, there should be a trigger why this sex change will happen.
I also have to put out here that once a female starts changing into a male, the reproduction of eggs stops immediately.
Sex change can also happen in other livebearers but that's rare. Members of the Xiphophorus genus (where swordtails and platies belong to) are most known of the sex change.
How interesting! Just amazes me how a fish can do that… aww noo maybe you’ll have better luck next time thank you very much for your reply.Your male looks like it may have started out female. Large fat body and a short sword is what is telling me this. Males tend to be smaller and thinner with long swords. Unless this is somthing specific to that variety of sword.
Swords can change from female to male. I'm not aware of any changing from male to female.
The ability for females to turn into males was the final nail in my sancho sword breeding project. 2 were lost to a food aggressive rhino pleco and the final female turned male leaving no females left to breed.
A shame, as I was guessing that generation was going to be stable and I'd soon have piles of white swords with orange circles on their heads.