Cotournix quail not growing at all!

[Buffalowingz]

Hi y'all I have 8 3wk old coturnix quail from my most recent hatch, 7 are growing as expected but one little one has not grown at all since week one- I've never seen this before. Is this little one a runt or is there a genetic condition etc.... seems healthy eats well very active, any ideas? Definitely not one for breeding stock. As you can see the little one at the top and pics below show comparison with siblings.

 

[DK newbie]

It happens from time to time.. This one seems pretty extreme though. It can go two ways: either it eventually weakens and dies, or it starts growing again and catches up with the others. I'm not sure what's causing it though - genes, disease or other factors.