One of the dwarf or "pygmy" Corydoras catfishes is the Corydoras habrosus; not usually reaching two inches in length. Otherwise, they are much the same, in my own observation, as any of the other Corys.
These catfish don't seem to show up very often in the pet stores, so when I found a tank full of young ones a year or so ago, I bought eight of them, hoping to get at least one male and one female. Soon after I got the fish home, two died, and when the rest grew up, I found that I had five males and one female left. Not exactly perfect, but a good enough ratio to give it a try.
I tried several methods over the next few months to get the fish to spawn, with little success. While the Corys in adjacent tanks on both sides of the Habrosus went into breeding frenzies, these fish refused. I gave up for a few more months.
In the spring of this year, I decided to give it another try before the fish were too old. I don't know how old is too old for a Corydoras, and I've heard they can live a very long time, but the fish had stopped growing, the female was heavy, and it seemed like a good time to try again.
I set up a ten gallon tank in another part of the basement, away from the 80+ degrees of the fish room, where the air stays cooler; about 72 to 78 degrees. The water was straight out of the tap, about 7.4 pH, and 8 degrees total hardness. No heater was used. An outside filter was added, with a thin sponge wrapped around the intake strainer. A few round stones, and some Java Fern attached to a piece of driftwood completed the setup.
The fish had not been conditioned any differently than before; feeding on a mixture of live, frozen, and dry prepared foods. The water in their tank had had 25% changed every week.
When the Corys were moved into the prepared tank, I started changing water daily, or at least every second day, with rain water. In ten days they started to spawn, and in four more days the female appeared to be depleted, so I removed all the adults.
It took ten days for the young to hatch, and they immediately started scouring the tank bottom for food in Corydoras fashion. There were a lot of places for the babies to hide, so it was difficult to tell how many there were.
The young ate micro worms for their first few days and newly hatched brine shrimp were added after that. They don't grow very quickly, but at present are almost three months old and the largest are about one-half inch in length.