You need a BGJD, i.e. a JD carrying the EB gene.
You can either breed a BGJD with a BGJD, or a BGJD and an EBJD.
BGJD x BGJD produces approximately 25% 'normal' JD, 50% BGJD and 25% EBJD.
BGJD x EBJD produces approximately 50% BGJD and 50% EBJD.
However as EBJDs are rather weak, they have a higher chance of dying than BGJDs or 'normal' JDs. So even if half the eggs are EBJD and the other half are BGJD, you may have considerably less EBJD fry, and then a lot less surviving until you can differentiate the two.
I have heard stories whereby pairs have consistently produced more EBJD than expected, not sure why that would be the case nor if it's really true. But yeah.
