Ah, except according to John Dawes book
Livebearing Fishes: A Guide to Their Aquarium Care, Biology and Classification, he suggests that female Poeciliids loose the further sections of their rib cages. That makes room for the growing fry.

Those extended sections of the males' ribs connect muscles to the gonopodium and they allow the male (guppy, swordtail, molly, et al) to maneuver the gonopodium so that he can fertilize a female. Even if a female experienced a profound hormonal shift and the anal fin narrowed into something close to a gonopodium (and that begs the question of whether viable sperm was produced), the probability is very great that no females would be inseminated.

Isn't it lyretail swordtail males who are unable to effectively mate with female swordtails? They have the conventional musculature, but the gonopodium is so altered that they are unable to mate with females. In at least one laboratory study, sperm has been withdrawn from a male lyretail sword and was effectively introduced to the eggs of a virgin female lyretail swordtail and she produced fry. How much more difficult would that be for a masculinized female?

It would be interesting if a researcher were to write a grant proposal for experiments with elderly, masculinized female swordtail and then try artificial insemination. Don't know how the writer would justify the expense other than just for the knowledge. "Pure research" of that sort, at a time when the economy is tanking and government and research money is getting scarce, may not get the attention of research with more practical applications.

Whoops! Look at the issues below, you might get your grant!

Sometimes fish born of inter-species crosses will be described as intersexes. That is, they show both male and female characteristics. I don't understand the survival advantage to either parent species because they are usually sterile. (Maybe predators go after - with less common appearance - rather than the parent species.) Aged female fish (guppies among them), who lose the ability to keep a balance of the testosterone and estrogen (among others?) will sometimes display male traits such as extended fin rays and more color.

Ah! Just for fun I Googled Masculinization of female fish. Wow! Got 68,000 hits. Many articles will send you to others!

Pollution has had profound effects on fish. I do now recall an article in the Potomac River systems where black bass have been showing up developing both testes and ovaries. They noted that:

> The discovery has made the South Branch the latest example of an emerging national problem: Hormones, drugs and other man-made pollutants  appear to be interfering with the chemical signals that make fish grow and reproduce.

http://www.nanfa.org/archive/nanfa/nanfa-loct04/0172.html

If you can get through the technical terms take a look at the ENVIRONMENTAL TOXICOLOGY article on
Masculinization of Female Mosquitofish in Kraft Mill Effluent-Contaminated Fenholloway River Water Is Associated with Androgen Receptor Agonist Activity.

I don't know if they credit completely masculinized female Gambusia with being able to sire young by inseminating other females. (Earthworms and many small pond snails are able to fertilize each other.) One immediate problem may be that there are so few females downstream from a paper mill that one wonders if there are enough females to carry the next generation.

http://toxsci.oxfordjournals.org/cgi/content/full/62/2/257

The Abstract of an article which was a "Report of a naturally masculinized female of the Clear Creek gambusia, Gambusia heterochir Hubbs" suggested that a masculinized female still carried 11 well-developed, late stage embryos. This suggested that the male looking female could still carry young.

http://www.blackwell-synergy.com/doi/abs/10.1111/j.1095-8649.1986.tb05141.x

It sounds like there are a lot of ramifications for the creatures living in these water and for those drinking them!

A summary of some of this stuff in the UK publication Practical Fishkeeping alluded to
"A seven year experiment on a lake in Ontario showed that chronic exposure to low levels of oestrogenic compounds resulted in the near extinction of these fish in the lake."

http://www.practicalfishkeeping.co.uk/pfk/pages/item.php?news=1608

Lesions on the skin, cancers, birth defects, reproductive anomalies, fish kills and more! Well you have sure opened the door on some interesting but disturbing stuff Josh!

I've impressed with what I don't know. If this is of interest, google topics like intersex fish, pollution and fish gender, feminized fish, maculinized female fish might include some of the areas on might search. Some of those are commercial academic sites, which want to sell you copy of the article. Search for the article itself and often you can find a complete copy of it on-line without having to pay $30 or $40 for it. Sometimes reading through the Abstract will give you what you need to know.