I think you can tell by candling because I have researched that chicken eggs will appear darker in the light if not fertile. Although I am not sure if that can be reliable. The eggs are coturnix quails.
I have two quail eggs given to me by some one who didn't know how to care for them, they're from a domesticated mother and father quail and are both shown fertile when candled. My family likes to keep the ac at 72-78 degrees Fahrenheit how long will the eggs last, I've always wanted to hatch egg...