How long to sex new babies?

[PlatyLady]

Why is it that whenever I have platy babies and guppy babies, they always look female to start off with? I am always in disbelief when I 'discover' that they are male. How old do they have to be before I can definitely tell their sex?

 

[TankGirl]

I believe they can be sexed at 3-4 weeks, with the males having the modified anal fin, or gonopodium. I have been searching on this issue because I have 2-week-old molly fry and they all appear to have the anal fin of a female. They develop relatively quickly, though, and start mating at 3-4 months. Happy spawning!

 

[Terry]

Spot on Tankgirl.

I believe they can be sexed at 3-4 weeks, with the males having the modified anal fin, or gonopodium.

No more to say, good luck with the babies.

 

[Sinuhe]

2 of my platies are too young to sex, even tho they are already 2cm/ almost an inch in size. That's the way most of the platies in the store were, nearly all looked like female, except for a couple of bigger ones that were starting to have a visible gonopodium. I'm pretty sure these platies are older than 4 weeks. I first saw them 2 weeks ago, and they were already almost this size then.

 

[platylover]

I think that where the fry are raised plays a big part as to when you can sex the fry. If they are raised in a breeder trap it may take a few months to sex them, where if they are raised in a larger tank, it may only take the 3-4 weeks.