When I was a kid, I kept killifish and while many mysteries had been figured out, there remained - at least to me, two questions that remained unanswered: first - why do some species or populations stay robust and healthy for tens of generations - while others are small, undercolored skinny fish that just seem to waste away in three years? Second why do some species of killi eggs have a high fertility rate (80-95%) while others... not so much. The large killies in the Fudulopanchax (Gularis, Gardneri and others) and especially the Aphyosemion sub-genus Raddaella can be problematical. I've bred Gularis many many times and had fantastic results in Canada and miserably dismal dismal results in California with fertility off 90+% - only 1-10% fertility there. Luckily hundreds of eggs still give enough for another generation, but for me there in that time and at that place, Tony Terceria's clever quote about Ps. annulatus that he told me on the phone around 1974 applies: "I can breed them, but I'll never have of hundred of them". .