Electric Blue JDs can be spawn from normal JDs just its like 1 in 500 or a 1000 or so, but they normall die off or are eaten by thier siblings for they are weaker. EBJD breeders know this and split up fry by size to give the EBJDs a better chance to survive. Now if you have 2 blue gene parents your odds of getting more EBJD fry goes up.
This pair is an EBJD dad and a normal mother with the blue gene, so all the fry will have the blue gene, and they should have more EB fry than 2 normals 50% or so.