super black and melano in fertility

I've been experimenting on spawning the blackest females from my melano x superblack line and so far I can only use the superblack female to carry the line. I've got a success once or twice in spawning with melano female (melano coming from above mix) but they ended up very weak genes.

Combination of spawn (there are other similar spawns performed on different pairs, i.e. 2 or 3 melano pairs involved):
F1a: melano x superblack-a
F1b: superblack x superblack

F2a: F1a x F1a
F2b: F1b x F1b
F2c: F1a x F1b
...

On each spawn, I took the blackest female x to any of melano male of either sibling or cousins in relationship. Other group members help spawning them and share the outcome together.

Numerous times I've got them successfully spawned with melano female but fry never last longer than 1 or 2 days after hatching. So, it seems, despite the female is fertile, the gene is not strong enough for the fry to live/develop. Disappointment comes when looking at an egg with head and tail formed lying on the bottom of the tank. It's either the fry doesn't fully develop or the process stops half way through.

Also, it's interesting to find out that there are 2 types of superblack females coming out of the above mix. The first type is a pure superblack with a hint of steel blue on its body (close to dorsal) and the second is without hint of steel blue. I suspect, the one with hint of steel blue is inheriting from melano and the one without hint of steel blue somewhat closer to the "pure" superblack. There are a number of females with half-superblack coloration, with red color not forming to full black coloration.

Anyway, will keep trying and see if the outcome is different on the next generation.