Breeding G. spengleri in captivity is not easy by any means. This species was once imported in large numbers and you could purchase adults for $30 each. While they were once cheap and easily obtained from importers wholesale lists, most died shortly after arriving into the country. High mortality, along with low clutch size, made for small numbers of captive bred hatchlings. Clutch sizes are usually 1 or 2 eggs, which 3 being an extreme rarity. I’ve only had one turtle lay three eggs and they were all small and deformed. My females usually lay one egg per clutch, and lay two clutches per year. So I get roughtly two eggs per year per female. This low reproductive rate is what keeps prices high for hatchlings. It’s also very difficult to hatch the eggs properly as they are very sensitive to temperatures and humidity.
As rare as captive bred G. spengleri are in captivity, captive bred G. japonica are almost unheard of. I am one of only a handful of people who have bred them in captivity in the United States. There have been no zoo captive hatchings of this species and only one private (AZA certified) institution has any specimens in their collection. No other zoos have them in captivity at this time. My adults were in captivity for many years before I was able to get eggs that were not crushed into pieces. I believe the adults try to eat the eggs or they break during the laying process and are then partly consumed. Once I had eggs that were not broken; I was lucky enough to have two fertile eggs and one hatched! I was only able to find two other people who had hatched them at that time and one was from a wild caught gravid female. Since then there may have been more captive success stories and I hope that there will be increased success with this species in the future. The eggs do not seem to be as sensitive as G. spengleri eggs.