ummm they are not a hybrid, just inbred. but yes they are weaker, if you are trying to breed them then your best bet would definitely be to get a female thats smaller than your ebjd and make sure you have a good divider handy. at the first sign of stress to the ebjd they will need to be separated, and yeah you obviously cant trust the lfs employee to differentiate sex since this one was clearly a male, the males will have a lot of coloring but the key is to look at the bottom half of the gill plate and the blue there will not just be spangling but will be smudgey as well. there will be blotches of smeared blue rather than the clear defined spangles of the male. if you are not trying to actually start a breeding project and just want a tank mate than i do not suggest another JD for your ejbd, you should do something more peaceful like a severum or something, what size tank is this?