Gah! Female Mollies Turning Into Male!

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I purchased 4 mollies a few weeks back that I believed were female, not sure of their age but they looked big enough in the shop at 1" plus to not be too young to be able to tell, or so I thought! they all started off with the fan shaped fin that denotes female but now one black molly has an obvious gonopodium, I always thought she was more aggressive now I know why
  now my dalmation looks to be going the same way and I only wanted females due to this aggression.
I still have one black and one silver molly who still have the fan shaped fins so I can only assume these are females but who knows, now I may end up with a tank full of males at this rate lol.
I have read various things on the net about late blooming males and that they can't change genders as they are born either male or female but I have also read they can indeed change as people have had females that have given birth that have then turned into males with gonopodiums, anyone know which it is?
 

fluttermoth

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They cannot change sex; it was thought possible for many years, but research has shown that not to be the case. It does happen in some genera of fishes (marine clownfish and wrasses, for example), but not in the common livebearers.

You can have late developing males, or old females can take on male characteristics as the levels of female hormones reduces as they reach the end of their reproductive life.
 
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Thank you for the response fluttermoth I thought this to be the case with livebearers, hoping mine are just late bloomers then rather than old girls! it does make it rather difficult to choose females in the shop though I did see obvious males in there too I guess choosing an obviously pregnant fish is the only way to be sure.
 
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Ah well I still love them, it seems all 5 I have are probably male I was wondering why none of them were appearing to be pregnant even though they were kept with obvious males in the shop, they are all slender and I have had them for the best part of 4 weeks now, I was so focused on the fin and thinking they were already adults due to their size....mollies are definitely the best in hiding it 
 
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