Butch's question in another thread about Amazon mollies reminded me of something I've been meaning to post about for awhile.
About a year and a half ago I collected a trio of P. latipinna from a tidal stream in Florida. By trio I mean one male and two females. They were all adult sized although the male was somewhat small despite being fully colored and sporting a full "sail" fin.
When I got them home, I put them into a planted 20 long with the intention of setting up a bigger tank soon. Soon after they acclimated, I noticed that the male only courted one of the females and that both male and female constantly chased and harrassed the other female. I found that odd as most livebearers I'd kept the males weren't choosy about who they mated and the females were not aggressive.
Well, it took me longer than expected to get them into a bigger tank and in the meantime the one female became gravid and eventually dropped about a dozen babies. The other female stayed hidden at all times and if it ever showed itself, it was instantly driven off by both male and female. Only the thick plant cover kept it from being harrassed to death and plenty of algae kept it well fed.
Eventtually I got around to getting the whole buch moved into a 30 gallon planted tank. Not long afterward, the outcast female went through an amazing growth spurt. She almost doubled in size, making her close to twice the size of the male and other female. That was odd, but even odder was the fact she was turning into a he! Almost overnight it seemed, "she" grew a gonapodium and big beautiful sail. Oddest of all however, was his/her behavoir! After months of being harrassed and bullied by the other two adults, the new male promptly killed both of the other adults with viscious, constant attacks!
Well, to make a long story a little less long, I came into a 90 gallon tank which I set up as my new planted tank and moved the freak male and the growing babies of the departed pair of mollies into it. Since then he has blossomed into a gorgeous fish and the babies have matured and several females have given birth to babies sired by the former female. Interestingly, of the offspring, I can easily tell male from female subadults long before any overt changes in fin shape. Yet my former female had me completely fooled!
Here's a couple shots of the King and his subjects.

Holy Ru Paul, Batman! Pictures and it did happen!

You always hear anecdotal stories about these kinds of things but this is the first time I've heard it told first-hand and taking place in an aquarium!

Alot of the stories you hear refer to "sex change" which is what I first was considering it as well. After looking into it I learned that true, functional sex change does not happen in live bearers as commonly believed [it does happen with certain marine species]. To be a true sex change, the "female" would have to be capable of giving birth and then later as a male to siring offspring. This did not happen here and the other two mollies' behavoir toward the "freak" showed that they sensed something odd about "Lola" that I could not see.
I've since learned of so called "sleeper males" which are males that retain outward characteristics of females in order to avoid aggression from dominent males. They bide their time and hide out in the harem untill the boss male is occupied elsewhere then make their move.
In this case I believe the close confines of the first 20 gallon tank and the small number of individuals defeated the sleeper stratigy and accounted for the aggression the oddball experienced. Once moved to a bigger tank and a higher population level, conditons favored the success of the sleeper. And successful he has been. He is much bigger and more colorful than the original male and is very potent, producing numerous offspring. So far, in his realm, none of the other obviously male offspring have asserted their maleness. Although colored and shaped differently from the females, and never courted by the male, they have yet to grow a gonapodium or sailfin. Not surprisingly, the big male ignores them and does not show aggression toward them. I believe this must be the natural behavoir in a group setting for this species.

Hi Mike. What you observed is very common. Male mollies mature along a size continuum, with some males maturing really early and being sexually mature at about a quarter inch. The others grow really big before maturing, and develop the intense color and big sail (like the fish in your photo.)

The thing to remember is that smaller males don't get that much bigger with time.

Joel Trexler at Florida International University has studied this. If you google him and his Web site, he may have a few papers explaining the phenonmenon.

Hi Mike. What you observed is very common. Male mollies mature along a size continuum, with some males maturing really early and being sexually mature at about a quarter inch. The others grow really big before maturing, and develop the intense color and big sail (like the fish in your photo.)

The thing to remember is that smaller males don't get that much bigger with time.

Joel Trexler at Florida International University has studied this. If you google him and his Web site, he may have a few papers explaining the phenonmenon.

Some crayfishes (Orconectes spp.) do something similar. Some males mature sooner and become sexually active at a smaller size. They dominate sexually immature although larger males that mature later in the season that in can in turn become domimant over smaller sexually mature males. Risk for later maturation is that if it does not occur before water level or temperature drop at ending the breeding season then reproduction will have to be post-poned until next year.

Hi Mike. What you observed is very common. Male mollies mature along a size continuum, with some males maturing really early and being sexually mature at about a quarter inch. The others grow really big before maturing, and develop the intense color and big sail (like the fish in your photo.)

The thing to remember is that smaller males don't get that much bigger with time.

Joel Trexler at Florida International University has studied this. If you google him and his Web site, he may have a few papers explaining the phenonmenon.

Thanks for the tip Bob! I bookmarked Trexler's web page so I can go back and read his many papers. It's cool that he makes his work available like that. I don't subscribe to any scientific journals so whenever I Google up a really interesting paper, all I usually get is the abstract.

Sure. I mispoke. I wrote mollies. I know this is common in P. latipinna and P. velifera, but I don't know if it occurs in any of the other species.

Thanks for the tip Bob! I bookmarked Trexler's web page so I can go back and read his many papers. It's cool that he makes his work available like that. I don't subscribe to any scientific journals so whenever I Google up a really interesting paper, all I usually get is the abstract.

Great looking fish. I went fishing yesterday and saw a few red mollies swim by . Doral lake in Miami. Didnt catch a thing but it was nice to see them.
Imagine released fish as they were regular orange color . Large size

something odd about "Lola" that I could not see.

That's an amazing song!

I've never witnessed "sex-change" personally, though I have heard a few stories. It seems that in those cases it was triggered by some drastic chemical change (i.e. jumping nitrate/nitrite levels). I would agree more, though, with your explanation of the male "dressing-up" as a female to curb aggression.

BTW, that is one beautiful sailfin molly!!!

Butch's question in another thread about Amazon mollies reminded me of something I've been meaning to post about for awhile.
About a year and a half ago I collected a trio of P. latipinna from a tidal stream in Florida. By trio I mean one male and two females. They were all adult sized although the male was somewhat small despite being fully colored and sporting a full "sail" fin.
When I got them home, I put them into a planted 20 long with the intention of setting up a bigger tank soon. Soon after they acclimated, I noticed that the male only courted one of the females and that both male and female constantly chased and harrassed the other female. I found that odd as most livebearers I'd kept the males weren't choosy about who they mated and the females were not aggressive.
Well, it took me longer than expected to get them into a bigger tank and in the meantime the one female became gravid and eventually dropped about a dozen babies. The other female stayed hidden at all times and if it ever showed itself, it was instantly driven off by both male and female. Only the thick plant cover kept it from being harrassed to death and plenty of algae kept it well fed.
Eventtually I got around to getting the whole buch moved into a 30 gallon planted tank. Not long afterward, the outcast female went through an amazing growth spurt. She almost doubled in size, making her close to twice the size of the male and other female. That was odd, but even odder was the fact she was turning into a he! Almost overnight it seemed, "she" grew a gonapodium and big beautiful sail. Oddest of all however, was his/her behavoir! After months of being harrassed and bullied by the other two adults, the new male promptly killed both of the other adults with viscious, constant attacks!
Well, to make a long story a little less long, I came into a 90 gallon tank which I set up as my new planted tank and moved the freak male and the growing babies of the departed pair of mollies into it. Since then he has blossomed into a gorgeous fish and the babies have matured and several females have given birth to babies sired by the former female. Interestingly, of the offspring, I can easily tell male from female subadults long before any overt changes in fin shape. Yet my former female had me completely fooled!
Here's a couple shots of the King and his subjects.

You had a male all along.Both sexes look the same till the mating instinct kicks in.In fact many males never fully develope large fins or bright colors.In less than ideal situations males never color up at all,just develope gonopodiums.In many fish sex is not the clear cut difference it is with mammals. In my area as the environment gets more degraded fewer males develope the beautifull fin and colors.