I have almost a year experience now with these fish. Very little, but I have learned a few things on my own and confirmed some of them through contacts with others who have raised these little gems. I have gotten eggs and raised fry from cynostyctum blue, cynostyctum Makokou, georgiae, fulgens and abacinum. I am raising enough to at least do a reasonable distribution of pairs in the hobby. I have found very few sources of Diapteron and therefore must assume they are not an easy fish. They do not seem difficult to breed, just a lot of work, time and care of fry. For me, these are definitely not a high production fish like many killies can be. This may be resulting in few pairs being raised thus the limited availability.
First, you need soft cool water. Mine have bred successfully at temperatures between 65 and 71 degrees F. (18 to 22 Centigrade) Water harder than 60 ppm TDS resulted in white (infertile) eggs. I have not gotten eggs above 72 degrees F. Eggs are large for such a small fish (almost gardneri size eggs). The eggs turn amber in color after a few days. A little salt in the water does no harm.(Received some adults with salt-enough to raise a TDS meter reading to 200 ppm. Maybe a teaspoon per 5 gal of water?) I do not use salt however, since it makes use of a TDS meter for measuring relative hardness very difficult. I use straight Reverse Osmosis water with addition of RO right (Kent product) for all my killies including the Diapteron adults. Lighting is not strong, only 6 florescent ceiling bulbs(three fixtures) in a 12 foot by 20 foot room.
Adults accept frequent water changes well but can live in pretty foul water( I raised one georgiae fry, now near adult size, (was of unknown parentage -haven't we all done that with a "single egg" early on?, in a one quart plastic tank with about two inches of water --no change of water, just minor additions and gunk removal via a baster upon occasion) He( I cleaned the gunk enough to finally see him) is doing just fine. Now to see if he can adapt to clean water.
Fry will die in water changes overnight. I am talking 5 to 10% fresh water dripped into the container thru a pinched airline overnight. Fry do well only in old tank water additions. I have lost entire tanks (5 gal tanks-2 inches of water deep) of 30+ fry up to 1/4 inch(1/2 cm) in size with very minor and careful water changes(water of the same pH, TDS, and temperature!) I am now using water from another tank, diluted 50% with new water and held for a few days prior to use. With 1/4 inch fry it seems to work.
For now until I can retire hopefully in a few years, I can only fed once daily, and feed newly hatched Brine Shrimp. With this feeding fry take about 6 months to show signs of sex. Parents ignore fry and eggs. My males do get along adequately together. I have not seen signs of real fighting despite things I have heard. One 5 gal tank has two pair and produces eggs and ignore fry as well as similar tanks with a single pair with no injury to females or males. Eggs are frequently found in the tight area of the mop at the top(floating or sunken has no discouraging effect) but will be also found in the full region of the mop. One to three eggs in a locale. Eggs take about 3 weeks to incubate. Sometimes with near 100% success, other times with 100% loss. I use no chemical additives for "protection"of eggs. Eggs as well as fry cannot tolerate fresh water addition(eggs may hatch prematurely with fatal results if fresh water is added. Light seems to have little or no impact on egg incubation success. I am told, but have not confirmed that with daily 90% water changes fry will do well, but this must be maintained so their water is always the same. As I said, I have not confirmed this.
I was told by a collector that the adults live in about 2 cm of water in the wild. My 5 gal tanks are half filled with water(above a sponge filter outlet) with no adverse results. Adults do like cover in the mop, however do venture out to be seen. Fry however, panic at any sign of open space and will go into shock(usually surviving after a few minutes floating upside down as if dead) if the mop they are in is moved. This seems to be typical until adult color is achieved at about half size((1/2 inch)
Not much information but probably more than you can find any other single place.