This subject has been pretty much laid to rest as to the cause not being genetic. A number of people have collected sunubbers, grown them out and spawned them and gotten perfectly good fry with no snubbers.
I am a hobby breeder and since my breeding group started spawning for me in May 2006 I have had about 500 fry perhaps more. I have gotten 4 or maybe 5 snubbers all told. I normally give/send them to Barbie on the west coast as she is one person who has dealt with this issue for a longer time than I have.
Basically, the accepted thinking is that this problem is associated more with eggs being too thick/hard for the fry to push through and break free initially or else from being pressed into the rear of a cave with flat surfaces.
To the best of my knowledge there are no snubbers captured in the wild according to the fishermen who have been interviewed.
New dads often take a spawn or two to get it right. if you are having eggs come out of caves you can place something under the fron end of the cave so it has a slight tilt towards the rear.
When I am forced to pull eggs/wigglers I now usually use this air powered hang on the front trap which recirculates tank water:
http://www.kensfish.com/aquarium-suppli ... large.html
Everything you ever wanted to say about "Zebra luvin", but didn't because you thought everyone would take the mickey! Plus general topics for discussion including everything from what you feed them to your personal experiences.
Interesting. I left these eggs in the separate tank for a few days and then artificially "hatched" them. A few of them popped out of their shells just fine but some took some doing by blowing on them with a pipette. The best way I can describe it is if you have ever taken a frozen pea and popped it out of its skin/shell. I'm sure the male does this in nature so I figured I'd better be the one to do it.