What a shame, we could have traded young fish to get new blood into our breeding stock.. although that isn't really a problem for you I guess
I've heard quite a few reports of the first spawn to fail, but not necessarily because the first spawn is infertile, even though I don't doubt that happens as well. Often the failure of producing young ones in the first spawn are due to the the males inexperience, so he either ends up eating the eggs, or the fry are get out of the cave at a far too early age, so gets eaten by other fish.
The latter happened in my first spawn, he ate most, and the rest ended up outside the cave while they were newly hatched. Luckily I was there to rescue the three refugees that made it out of the cave, and they are still happy and healthy
