When can you tell the sex on fry?

I have some balloon molly fry, they are a couple of weeks old. When should I be able to tell the sex? And when will they start mating, (I don't want the siblings to mate.) Thanks!

 

Hi,

Mollies usually become sexually mature at around 30 days old. I believe that's the right number. I might be off by a bit though. You should be able to sex them young. You can sex by their analfin. The female's is fan shaped while the male's is pointed.

 

k, that's what I thought, pretty sure I have all females. which is good, my male to female ratio is high. I hope its not 4 weeks, these guys are still pretty small, like 2/3 inch.

 

While they are young, they all appear to be females.

Generally, I spot it thru behavior than thru the fins.

You will see the males attempting to breed, even before they are able to do any thing.

 

ha! it must be a "male" thing! lol! I will have to keep an eye on them. Maybe I will be able to indentify gentilia in the next few weeks.

 

I have raised Mollies for years and I have never personally been able to sex them until they are at least 6 to 8 weeks old. Guess my eyes aren’t as good as some others are. I have never had any female under 6 months old give birth in any of my tanks.

I keep all my fry in 30 gallon grow out tanks for their first 6 months. By then they are easy to sex and the males have started to follow the females around but I have never seen any births in the “grow out tanks”. Once my fry have grown into nice sized juveniles I sell them to my local fish store.