from what bro dalelad said, i take it as no.
Stunt was usually due to later state of the fishes after birth due to human fault !?( then again pls correct me if im wrong)
Deform might be by birth. I dont think even both parent perfect, all frys will be perfect. U still get 1, 2 deform.
that what culling is for
though ahh i dont have the heart.