EBJDs are the result of a semi-lethal recessive gene mutation that reduces the typical pigmentation of the fish, giving rise to the truly-sweet electric-blue colouration. They are a natural variant, however, they aren’t found in the wild because the weaker blue fry do not survive. The double-dose of the blue gene causes the EBJD to grow much more slowly and become a tad less nasty than its wild-type counterpart. As a result, blue fry must be carefully separated from their black brothers and sisters and raised in isolation in order to survive. This was originally done by a fellow named Hector Luzardo in 1985. Slower growth also means that while your EBJD and JD juveniles may be the same size when you purchase them, they will be of radically different sizes within a few months. You will probably have to give your original EBJD some lead time to grow before getting him/her a mate.
To further complicate the issue, the inherent weakness of the EBJD means that if two EBJDs are mated together directly, while they will indeed produce 100% EBJD offspring, these offspring will be so weak, the pairing will almost surely also result in 100% dead offspring. So, how do we obtain blue offspring if we can’t use the blue fish to do it, you may ask? The answer lies in making use of blue-gene carriers, as was originally done when these fish were first discovered. The fish that carry the gene, but look like regular ol’ Jack Dempseys, are known as BGJDs, blue-gene Jack Dempseys.
