Can you sex fry?

Is there a way of knowing what sex a BN will be when they're fry?

I can see that my first batch, now that they're about two months old, are clearly two different sizes. Some significantly larger than others. I'm wondering if the larger are males and the smaller females?

I wonder mostly because I would like to keep one albino male if I have one, and a common female perhaps. (though I'll need a third tank.... oh well!   )

Any hints, tips or suggestions?

size no i have a male here that is half the size of some of my females

nope, sorry. You generally have to wait til they are about 3cms and even then it is still a solid guess. 5cms is where is becomes apparent

I was told by another forum mate who had it on good authority that a reliable way of testing is if the top of the head is soft it's going to be male ..hard it's female.
Any one else heard that?

Did this mate have his head tested???

Not sure .I'm keeping an open mind on his idea though.

Ok. Make an experiment and please let me know how did it go. How hard do I need to push to tell it's soft?  

I have heard this too. I gave it a go but must admit i had no idea how hard to push and given that I was not wanting to smush the little fellas and they were already stressing at being out of the the water I gave it a miss. The few that I tried though i could not feel any difference. I had more luck with body shape when they were younger, used to run at about 70-80% right.